Microfibrillated cellulose prepared by electron beam irradiated pre-treatment – a comparison of various influencing factors with regard to material and process

Microfibrillated cellulose prepared by electron beam irradiated pre-treatment – a comparison of various influencing factors with regard to material and process | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Microfibrillated cellulose prepared by electron beam irradiated pre-treatment – a comparison of various influencing factors with regard to material and process Johanna Fischer, Michael Thomas Müller, Katrin Thümmler, Björn Günther, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9028732/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract An innovative approach for the production of microfibrillated cellulose (MFC) using a combination of high-pressure homogenization and electron beam irradiation (EBI) pre-treatment is proposed. In contrast to conventional pre-treatments for the production of MFC, electron beam treatment is a completely chemical-free method. This study focuses particularly on the extent to which the conditions of the electron beam irradiation, in terms of dose, dose rate, and atmosphere, influence the properties of the pulps and the resulting MFC. The effects on the both pulp types kraft pulp (KP) and sulfite pulp (SP) were compared. An irradiation dose of 100 kGy already leads to a significant decrease in the intrinsic viscosity of both types of pulp, while the crystallinity of the samples remains largely unaffected. It was demonstrated that EBI with a suitable irradiation dose, which varies greatly in dependence on the pulp type, is a promising approach for fast, effective, and chemical-free pre-treatment. pulp irradiation microfibrillated cellulose electron beam irradiation high-pressure homogenization Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Introduction There is a growing demand in the daily life for the application of renewable, biodegradable, environmentally friendly, and recyclable materials that are highly abundant. In this context, microfibrillated cellulose (MFC) is attracting increasing attention in a wide field of applications due to its attractive properties with regard to a high strength, low weight, dimensional stability, high optical transparency and non-toxicity. Currently, MFC is mostly used in paper and paperboard applications as a strength additive or for surface coatings, and in food applications for barrier coatings. However, it can also be used for medical, cosmetic and pharmaceutical applications (Osong et al. 2016 ; Stenstad et al. 2008 ; Siró and Plackett 2010 ). Microfibrillated cellulose, alternatively referred to as nanofibrillated cellulose, consists of aggregates of cellulose microfibrils with a thickness in the range of 20–60 nm and a length of several tens of micrometers (Lavoine et al. 2012 ; Siró and Plackett 2010 ; Phanthong et al. 2018 ). Another type of nanocellulose is cellulose nanocrystals (CNC), also known as cellulose nanowhiskers, which have a diameter of 2–20 nm and a length of 100–500 nm (Phanthong et al. 2018 ; Siró and Plackett 2010 ). Because CNCs are extracted from cellulose chains through acid hydrolysis, they have mainly crystalline regions. In contrast, MFC consists of both amorphous and crystalline parts, and usually forms rigid, web-like networks (Siró and Plackett 2010 ; Lavoine et al. 2012 ; Osong et al. 2016 , Phanthong et al. 2018 ). As sources for producing MFC, wood pulp is mainly used, but agricultural crops and their by-products, as well as bacterial cellulose, are also viable sources (Siró and Plackett 2010 ). In 1983, Herrick et al. ( 1983 ) and Turbak et al. ( 1983 ) first described a method for producing MFC whereby a dilute cellulosic wood pulp-water suspension was passed through a mechanical homogenizer under high pressure. Presently, the predominant method of MFC production involves mechanical treatment and high-pressure homogenization. For the high-pressure homogenization a microfluidizer equipped with different chambers is used, where high shear rates promote the formation of very thin and uniformly sized cellulose fibers. Other methods of producing MFC include grinding, cryocrushing and electrospinning. All methods for the fibrillation of cellulose fibers to microfibrillated cellulose require intensive mechanical treatment and, consequently, result in high energy consumption. Therefore, pre-treatments are recommended to reduce the energy input. Alkaline, enzymatic, TEMPO-mediated oxidation and carboxymethylation pre-treatments are proposed (Siró and Plackett 2010 ; Lavoine et al. 2012 ; Vanhatalo et al. 2016 ; Coura et al. 2025 ). Wood pulp is predominantly used for the production of MFC, which can have a wide range of properties depending on the pulping process and the type of wood used. The kraft process is mainly utilized for producing pulp, which is characterized by its high strength in comparison to alternative chemical pulping methods (Santos et al. 2012 ; Young 1994 ). In contrast, sulfite pulp is more readily bleached and refined compared to kraft pulp, and the unbleached sulfite pulp is significantly brighter. In addition, sulfite pulps have been shown to possess a higher swelling capacity and a broader molecular weight distribution (Sixta 2006 ; Duan et al. 2015 ; Young 1994 ). Another major difference between the pulps derived from the acid sulfite pulping and the kraft pulping processes is the destruction of the primary cell wall. While acid sulfite pulping completely destroys the primary cell wall, kraft pulping leaves it largely intact, which can lead to significant differences in subsequent refining (Sixta 2006 ; Duan et al. 2015 ). In addition to the type of chemical pulping, the raw material used is also very decisive for the properties of the pulp. For instance, the fibers of softwood are significantly longer than those of hardwood in the kraft process (Lapierre et al. 2009 ). Electron beam irradiation (EBI) can improve the physical and chemical properties of materials and can be used for many different purposes, including cross-linking of polymers, degradation of materials, polymer backbone modification, surface functionalization, and sterilization of medical equipment (Krieg et al. 2023 ; Huang et al. 2019 ; Leopold et al. 2023 ; Müller et al. 2020 ; Davila et al. 2021 ). Therefore, thermally generated electrons were accelerated by an electromagnetic field and guided along the beam tube to modify the samples. The advantages of electron beam irradiation for modification, particular of biomass, are that the method is completely chemical-free, has a short process time, and can be carried out under convenient conditions (room temperature, atmosphere, ordinary pressure) (Sarosi et al. 2020 ; Choi et al, 2008 ; Lee et al. 2018 ; Zhang et al. 2024 ). Furthermore, the parameters of the radical-induced chemical reactions can be precisely controlled by adjusting beam parameters such as beam current and energy. The effects of ionizing radiation on cellulose and other polysaccharides are studied in literature (Ershov 1998 ; Charlesby 1955 ; Ershov and Klimentov 1984 ; Sun and Chmielewski 2017 ). A high-energy electron treatment of cellulose results in the generation of polymer chain radicals, which are formed along the cellulose backbone induced by ionization and excitation. Alternatively, radicals may be generated via water radiolysis, followed by subsequent radical transfer to the polymer backbone (Sun and Chmielewski 2017 ). The polymer radicals react further predominantly via chain scission and depolymerization. Such chain scission reactions alter the polymer structure and consequently change the properties of cellulose with regard to crystallinity, chemical reactivity, mechanical behavior, surface energy, molar mass, and solubility (Charlesby 1955 ; Ershov 1998 ). Furthermore, electron beam irradiation can introduce oxidized groups, particularly carbonyl and carboxyl groups, whereby the proportion increases with a higher EBI dose (Saeman et al. 1952 ; Henniges et al. 2013 ; Sarosi et al. 2020 ; Fischer et al. 1987 ; Ershov and Klimentov 1984 ). Radicals at C1 and C4 positions cleave the 1,4-glycosidic bond, which leads to chain scission and the formation of aldehyde groups (Sun and Chmielewski 2017 ). The radicals localized at C2, C3 and C5 positions lead to the formation of carbonyl groups, without causing scission reactions (Ershov 1998 ). At very low irradiation doses, also cross-linking of cellulose can occur instead of chain scission (Choi et al. 2008 ; Lee et al. 2018 ). In addition to the EBI dose, other factors play a significant role upon the electron beam treatment of pulp including moisture content, temperature, working atmosphere, and the structure and composition of the starting material (Sarosi et al. 2020 ). However, there have been no comprehensive studies on the effects of EBI on different pulp types as well as on pulp irradiation of wet material or irradiation under nitrogen atmosphere. Until now, only a few studies have used electron beam irradiation as a pre-treatment for the preparation of cellulosic nanomaterials like microfibrillated cellulose or cellulose nanocrystals. Lee et al. ( 2018 ) employed EBI as a pre-treatment for the preparation of CNC from dissolving softwood pulp, where irradiation doses > 500 kGy were applied for the direct production of CNC after irradiation. At lower irradiation doses, the preparation of CNC is carried out by alkali treatment. Nedon et al. ( 2021a ) also proposed electron beam irradiation as a pre-treatment for producing nanocellulose particles to be used for the restoration of paper substrates (Nedon et al. 2021b ). Wu et al. ( 2024 ) investigated the suitability of waste cotton fabrics as starting material for the production of cellulose nanorods using EBI pre-treatment. EBI has also been utilized as a pre-treatment process followed by acid hydrolysis in order to produce nanocellulose from various starting materials, such as kenaf (Kim et al. 2016 ), cotton linter (Hai and Seo 2016 ), and bleached softwood kraft pulp (Hai and Seo 2017 ). This study investigates how the properties of cellulose are affected by electron beam irradiation, with the aim of making targeted adjustments. Therefore, different types of pulp (kraft pulp vs. sulfite pulp) were used, and the irradiation conditions were varied in terms of irradiation dose ranging from 100–400 kGy, dose rate, and atmosphere. The irradiated pulps are comprehensively characterized, in particular regarding to degradation (intrinsic viscosity), crystallinity (Raman spectroscopy and X-ray diffraction), morphology (Scanning Electron Microscopy), swelling behavior (Water Retention Value) and changes in fiber dimensions. These pre-treated, irradiated pulps were used to prepare microfibrillated cellulose by high-pressure homogenization. This two-step preparation of microfibrillated cellulose (Fig. 1) is a suitable and sustainable way without adding any further chemicals into the process. Furthermore, it enables easy adjustment of the properties of the resulting MFCs. Figure 1 Scheme for the preparation of microfibrillated cellulose. Created with BioRender.com. Materials and Methods Materials Two different pulps prepared by kraft and sulfite process were used in this study. Northern Bleached Softwood Kraft pulp (KP) prepared from spruce and pine was provided by Mercer, Stendal and Bleached Hardwood Sulfite pulp (SP) prepared from beech by Lenzing, Austria. The chemicals used for the analysis were purchased from VWR or Carl Roth and were used as received. For all washing and dilution steps, deionized water was used. Electron beam irradiation (EBI) The pulp was cut into samples with dimensions of approximately 21 x 30 cm, which were then irradiated using an electron accelerator ELV-2 from Budker Institute of Nuclear Physics, Novosibirsk (Dorschner et al. 2000 ). The irradiation was carried out with a constant electron energy (1 MeV) and electron current (2–4 mA). Irradiation total doses between 100 ± 10 and 400 ± 40 kGy were applied at dose rates of 0.67 and 1.41 kGy s − 1 , which results in single-pass irradiation field doses of 5 and 50 kGy, respectively. For comparison, both dry (D) and wet (W) sheets were irradiated at different doses under ambient air. The wet sheets were moistened to their maximum water absorption capacity. In addition, each pulp sample was irradiated in a nitrogen atmosphere (N 2 ) at a dose of 400 ± 40 kGy. 24 h after irradiation, the cellulose samples were immersed in water for 5 min to guench the existing radicals. The labelling of the samples is done in the following way: “ pulp _ dose _ dose rate _ atmosphere” , e.g., KP_400_50_D is a dry kraft pulp treated with 400 kGy at a single-pass irradiation dose of 50 kGy in an air atmosphere. High-pressure homogenization First, 30 g irradiated pulp was added to 1 L water and stirred for 30 min. Afterwards the suspension was dispersed with an Ultraturrax at 16,000 rpm for 90 min. The high-pressure homogenization was carried out using a 200-µm-chamber at a pressure of 360 bar and a 100-µm-chamber at a pressure of 1,000 bar for one hour each. Characterizations Chemical composition For the analysis of the chemical composition of the pulps, the extract (TAPPI 1997 ), cellulose (Kürschner and Hoffer 1931 ), and Klason lignin content was determined. A detailed description of the methods can be found in Günther et al. ( 2021 ). High-Pressure Liquid Chromatography (HPLC) Prior to HPLC measurements, a hydrolysis of polysaccharides to monosaccharides with trifluoroacetic acid was carried out for the (irradiated) pulps (Fengel et al. 1978 ). In order to determine the hemicellulose composition, an HPLC analysis was performed on a HPLC unit Azura (Knauer) running at 80°C with a flow rate of 0.3 mL min − 1 (H 2 O) using Agilent MetaCarb87P columns and a RID2.1L detector (Knauer). Glucose, arabinose, xylose, and galactose were used as calibration standards, and calculations were performed using the ClarityChrom software. Intrinsic viscosity Determination of the intrinsic viscosity was carried out based on DIN EN 60450 ( 2008 ). The pulp samples were defibrillated in 25 ml water using a shaking device and afterwards 25 ml of CUEN solution were added. The specific viscosities (ν s ) of the samples were measured with an Ubbelohde viscometer by the outflow time of the CUEN pulp solution (t s ) and the outflow time of the CUEN blank solution (t B ). $${v}_{s}=\frac{{t}_{s}-{t}_{B}}{{t}_{s}}$$ 1 The intrinsic viscosity v was calculated from the specific viscosities v s , the concentration c and the Martin´s constant k (k = 0.14) with the empirical formula according to Martin ( 1951 ): $${v}_{s}=\left[v\right]\text{*}{c}^{k\left[v\right]\text{*}c}$$ 2 Water retention value (WRV) The WRV of the (irradiated) pulps was determined according to ISO 23714 ( 2014 ), and the fiber dimensions were measured using an L&W Fiber Tester following ISO 16065-1 ( 2014 ). Zeta potential measurements were performed to determine the surface charge of the (irradiated) pulps using a SZP 06 (Mütek GmbH). Scanning electron microscopy (SEM) SEM images of the (irradiated) pulps and the resulting microfibrillated cellulose were recorded using a FEI Quanta FEG 650 microscope at an accelerating voltage of 5 kV using a SE detector. All samples were sputter-coated with gold (JEOL JFC 1100E ion sputter) to minimize charging effects. Raman spectroscopy Raman measurements were performed using a MultiRam (Bruker Optik GmbH) with a laser power of 100 mW for microfibrillated cellulose and 300 mW for the raw material and (irradiated) pulp, at a wavelength of 1064 nm. The spectra were recorded over the range of 3500–5 cm − 1 with 100 scans, using an operating spectral resolution of 4 cm − 1 . The spectra were normalized and a baseline correction was conducted using the operating spectroscopy software OPUS Ver. 6.5 (Bruker). X-ray diffraction (XRD) The X-ray diffraction patterns of the (irradiated) pulps were carried out at a STOE STADI P powder diffractometer using Cu Kα 1 radiation of 1.54056 Å wavelength, a scan range between 5° < 2θ < 100°, and a step size of Δ2θ = 0.01°. The crystallinity index (CrI) was calculated as follows by the method of Segal et al. ( 1959 ): $$CrI=\frac{{I}_{002}-{I}_{am}}{{I}_{002}}\text{*}100$$ 3 where I 002 is the maximum peak intensity of the 002 Bragg reflection at 2θ = 22.5°, while I am is the peak intensity of the amorphous region at 2θ = 18–19°. Fourier transform infrared spectroscopy (FTIR) FTIR measurements were performed at a FTIR spectrometer Tensor27 (Bruker Optik GmbH). For each measurement, a spectrum with 32 scans and a resolution of 4 cm − 1 was recorded over the range of 400–4000 cm − 1 . 13C NMR measurements 13 C solid state NMR measurements were carried out at 100.6 MHz on a 400 MHz Bruker AVIII HD WB spectrometer equipped with a CP/MAS probe using 4 mm ZrO 2 rotors at 10 kHz spinning speed. A contact time of 1 ms with an 80% ramp on the 1 H channel was applied for CP, experiment recycle delays were 3 s, the acquisition time 35 ms, and a spinal64 decoupling sequence was applied during acquisition. 10000 scans were accumulated. The chemical shift was referenced externally using the CH 2 -group signal of adamantane (38.5 ppm with respect to TMS = 0 ppm). To calculate the crystallinity of the (irradiated) pulps, the crystalline part at the C4 atom was integrated in the range from 92 -86.6 ppm. Particle size measurements The particle size distributions of the microfibrillated cellulose after dispersing as well as after high-pressure homogenization in different chambers (200 µm and 100 µm) were determined using a laser diffraction particle analyzer Mastersizer 3000 (Malvern), the data were analyzed using the Mie Model. Dynamic light scattering measurements were carried out on a Horiba LB-550 in the size range of 0.001 to 6 µm. Size exclusion chromatography (SEC) For determining the molar mass of the pulp, irradiated pulp and MFC samples, SEC was used at 30°C with a setup containing a LC-10AD VP pump, two columns (PSS SDV guard, PSS SDV lin M), UV-vis and refractive index detectors. As eluent, THF with a flow rate of 1 mL min − 1 was used. The samples have to be carbanilated before the SEC measurements to make them THF-soluble. Results Characterization of the raw material For the irradiation experiments, kraft pulp (KP) and sulfite pulp (SP) were used in order to investigate the influence of the EBI treatment on the different kind of pulps. Both pulps are almost free of lignin, with Klason lignin amounts < 0.05%, and have an extractive content of about 0.4%. The cellulose content of kraft pulp is 93.4%, while that of sulfite pulp is 94.5%. HPLC measurements show a very high proportion of glucose within the both samples of 82% in kraft pulp and 97% in sulfite pulp. Kraft pulp contains a higher proportion of hemicellulose consisting of 7.5% xylose, 5.8% of mannose, 0.4% arabinose and traces of galactose, whereas in sulfite pulp only about 1.4% xylan and 0.6% mannose can be detected. The M N value of the kraft pulp sample is 368,210 g mol − 1 . Sulfite pulp shows a smaller M N of 178,870 g mol − 1 , but has a broader distribution, which indicates higher polydispersity. The differences of the molecular mass result mainly from the different pulping processes (Duan et al. 2015 ). The SEM images in Fig. 2 show the morphological fiber structures of both pulp samples. While the kraft pulp fibers have a relatively flat and straight shape, those of sulfite pulp have a tube-like form. Further differences between the two pulps can be determined in their surface structures. The fibers of kraft pulp have a predominantly smooth surface with occasional peeling of the fibers, whereas the surface of sulfite pulp is rather rough due to defibrillation and peeling of the fibers. The measured average fiber widths of 28.6 µm for kraft pulp and 21.2 µm for sulfite pulp are in accordance with the fibers shown in the SEM images. The average fiber length is approximately 2.1 mm for kraft pulp and about 0.72 mm for sulfite pulp. Influence of the irradiation dose The aim is to investigate how the electron beam dose influences the properties of the pulp, and to examine the differences between kraft pulp and sulfite pulp due to irradiation. The dry kraft pulp (KP) and sulfite pulp (SP) sheets were treated with electron beam doses in the range of 100–400 kGy at a dose rate of 1.41 kGy s − 1 . The intrinsic viscosities of kraft pulp and sulfite pulp before irradiation are 484 ml g − 1 and 352 ml g − 1 , respectively. Even with an irradiation dose of 100 kGy, a rapid decrease in the intrinsic viscosity can be observed, reaching values of 73 ml g − 1 (KP) and 71 ml g − 1 (SP) (Fig. 3 a, Table 1 ). The irradiation initiates chain scission due to the splitting of glycosidic bonds, leading to the depolymerization of cellulose and as a consequence, in reduction in intrinsic viscosities. An increase of the EBI dose up to 400 kGy results in a further, albeit slight, reduction in the intrinsic viscosities. The rapid decrease in intrinsic viscosity or degree of polymerization (DP) at EBI dosages < 100 kGy, followed by a further slight decrease until the so-called level-off DP (LODP) has also been reported in other studies (Driscoll et al. 2009 ; Wu et al. 2024 ; Lee et al. 2018 ; Charlesby 1955 ). While kraft pulp has a higher intrinsic viscosity compared to sulfite pulp before EBI, the EBI treatment leads to very similar values for the both pulp types with 29 ml g − 1 (KP) and 31 ml g − 1 (SP). The very slight differences in intrinsic viscosity between the two pulp types can be explained by the high degradation of cellulose by EBI up to the LODP. In contrast to the intrinsic viscosity, the fiber length of the kraft pulp remains nearly constant during the EBI treatment up to an EBI dose of 200 kGy, with values of around 2 mm (Fig. 3 b). Higher EBI doses lead to a reduction in fiber length of up to 0.8 mm at 400 kGy, which corresponds to 40% of the starting material. Sulfite pulp generally has a significantly shorter fiber length of the raw material with 0.7 mm due to the pulping process and the use of hardwood. Irradiation of the pulp leads to a slight, but steady shortening of the fibers, reaching 0.4 mm at 400 kGy (58% of the initial length). In principle, it can be expected that irradiation leads to a shortening of the fibers due to defibrillation, but the extent depends strongly on the type of pulp used. For both pulp types, the fiber width initially decreases slightly (KP) or remains stable (SP), but at a higher irradiation dose, the fibers become somewhat wider (Fig. 3 c). This effect of the fiber widening is probably related to the swelling of the fibers due to irradiation and increases with a higher irradiation dose. Choi et al. ( 2008 ) observed similar effects of fiber swelling with alkali treatment of kraft pulps, increasing the NaOH concentration leads to an increase of the fiber width. The WRV of the pulp is investigated by a standard centrifugation technique that measures the amount of water, which remains in the pulp and is related to the swelling behavior. The WRV is influenced by many different factors, such as fiber morphology and composition of the pulp (Mayr et al. 2017 ; Botková et al. 2013 ). Another influencing factor on the WRV is the amount of hemicellulose due to its contribution to the interfibrillar bonding (Koistinen et al. 2024 ). Chen et al. ( 2009 ) show that a decreasing amount of pentosane leads to a decrease of the WRV. The water retention capacity of the kraft pulp is with 87.4% significantly higher than that of sulfite pulp with 64.6%, which might be caused by the higher amount of hemicellulose in the kraft pulp sample as well as the different fiber structure, especially fiber length, of the materials (Fig. 4 a). A decrease in the WRV is observed for both pulp samples after EBI treatment, for KP there is a slight increase at an irradiation dose > 300 kGy. Previous studies by Fischer et al. ( 1987 ) also detect a decrease in WRV values with increasing irradiation dose. However, no correlation was found between irradiation dose and WRV, an irradiation dose of 400 kGy leads to values of 66.7% for KP and 50.5% for SP. It is assumed that the reduction of WRV is primarily related to the degradation of hemicellulose during EBI treatment, as the hemicelluloses are able to bind large quantities of water (Koistinen et al. 2024 ; Dias et al. 2019 ). The zeta potential measurements should provide information about the surface properties of the pulp samples. Different electrokinetic effects can be used to determine the zeta potential. The streaming current or streaming potential method, employed in this study, is most suited for measuring fibers (Jacobasch et al. 1985 ). Since the zeta potential depends not only on the surface potential of the pulp, but also on the properties of the liquid phase, a dependence on the pH-value must be considered. However, fluctuations in the pH range 6–9 only have a minor effect on the zeta potential values (Anikushin et al. 2022 ). Due to the presence of carboxyl and hydroxyl groups by suspension of the pulps in water, a negative charge is measured. The kraft pulp has a zeta potential of -22 mV, which is in accordance with results of other studies on bleached kraft pulp samples (Bhardwaj et al. 2004 ). The irradiation of the kraft pulp does not lead to changes in the zeta potential and values are within in the range of -20 to -28 mV (Fig. 4 b). The sulfite pulp has a similar zeta potential of -21 mV before irradiation, but the value increases significantly to -59 mV by an irradiation dose of 400 kGy. It is assumed that the number of functional groups is significantly increased for the sulfite pulp by irradiation. Changes with regard to porosity, pore structure and swelling capacity can also influence the zeta potential and lead to a higher surface charge of the material (Stana-Kleinschek et al. 2001 ; Luxbacher 2020 ). In addition, the drainage resistance was measured using the Schopper-Riegler (SR) method in accordance to EN ISO 5267-1 ( 2000 ). The values for the raw material as well as irradiated pulp were in the range of 9 to 13 °SR. These values are within the range assigned to unground pulps, and no dependence of the SR values on the applied electron beam dose can be determined. Table 1 Properties of kraft pulps and sulfite pulps with various irradiation dose. Kraft pulp (KP) Radiation dosage [kGy] Intrinsic viscosity [ml g − 1 ] Water retention [%] Zeta potential [mV] Fibre length [mm] Fibre width [µm] CrI (XRD) [%] CrI (NMR) [%] 380/1096 0 484 87 ± 0.54 -22 ± 0.05 2.07 ± 0.010 28.6 ± 0.00 84.0 48.4 0.43 KP_100_50_D 100 73 62 ± 0.19 -24 ± 0.60 2.11 ± 0.009 27.6 ± 0.00 84.8 - 0.42 KP_200_50_D 200 50 61 ± 0.86 -28 ± 0.05 2.00 ± 0.004 27.8 ± 0.05 84.7 - 0.41 KP_300_50_D 300 32 67 ± 0.67 -20 ± 0.05 1.17 ± 0.001 27.7 ± 0.00 82.5 - 0.40 KP_400_50_D 400 29 67 ± 0.46 -23 ± 0.85 0.82 ± 0.001 29.9 ± 0.05 83.5 45.3 0.38 Sulfite pulp (SP) 0 352 65 ± 0.58 -21 ± 0.10 0.72 ± 0.003 21.2 ± 0.00 84.2 47.7 0.48 SP_100_50_D 100 71 50 ± 1.24 -49 ± 0.05 0.69 ± 0.003 21.7 ± 0.00 84.6 48.3 0.46 SP_200_50_D 200 49 48 ± 0.40 -56 ± 0.15 0.59 ± 0.001 22.1 ± 0.00 84.5 47.6 0.45 SP_400_50_D 400 31 51 ± 0.53 -59 ± 0.20 0.42 ± 0.001 22.9 ± 0.05 83.2 45.4 0.42 The degree of crystallinity is an important factor for the physical, mechanical and chemical properties of the pulps. An increasing degree of crystallinity leads to a decreased swelling and chemical reactivity of the cellulose, while increasing its tensile strength and dimensional stability (Agarwal et al. 2010 ). In order to obtain information on the crystallinity of the pulps used here, Raman, XRD and NMR experiments were carried out. Raman measurements are an important tool for analyzing cellulosic materials because of the weak bands of water and background (Agarwal et al. 2010 ). To determine the crystallinity of cellulose, Schenzel et al. ( 2005 ) suggest using the peaks at 1481 cm − 1 and 1462 cm − 1 for the crystalline and amorphous parts of cellulose, in conjunction with spectral deconvolution. The deconvolution is necessary, since the intensities of the selected bands are relatively low, which can lead to band fitting problems. In contrast, Agarwal et al. ( 2010 ) propose a univariate analysis based on the peaks at 380 cm − 1 and 1096 cm − 1 bands. They detected a strong change in intensity and band shape at the 380 cm − 1 and 1096 cm − 1 caused by ball milling, which has a substantial impact on cellulose crystallinity. Schroeder et al. ( 1986 ), who found that the fibrous cellulose sample had a much higher intensity than the regenerated cellulose and ball-milled samples, also show the correlation of the band at 380 cm − 1 with the cellulose crystallinity. In this study, both the bands at 380 cm − 1 (Fig. 5b) as well as at 1462 and 1481 cm − 1 (Fig. 5c) were investigated in order to obtain information on the crystallinity of the both pulp samples and the changes resulting from electron beam irradiation. The Raman spectra in the range of 200–2000 cm − 1 of the kraft pulp and sulfite pulp as well as their samples irradiated with 400 kGy, depicted in Fig. 5a, show no significant variations. This leads to the assumption that the cellulose I structure remains mostly unchanged in all samples. For the band at 380 cm − 1 , a decrease in intensity with rising irradiation dose can be shown for both the kraft and sulfite samples, which was therefore accompanied by a slight decrease in the 380/1096 ratio. Generally, the sulfite pulp samples exhibit slightly higher intensities at 380 cm − 1 indicating a higher proportion of crystalline parts compared to the kraft pulp samples. The slight decrease of the values due to irradiation for the 380/1096 ratio can be detected for both pulp types in the same way with a decrease from 0.43 (raw material) to 0.38 (400 kGy) for kraft pulp, and from 0.47 (raw material) to 0.42 (400 kGy) for sulfite pulp. Figure 5 Raman spectra for raw materials and irradiated kraft pulps and sulfite pulps with a) full spectra and detailed view of a) the band at 380 cm − 1 and b) the bands at 1462 cm − 1 and 1481 cm − 1 . It is noticeable that in all samples, the pulps before and after irradiation, the peak at 1481 cm − 1 shifts to a wavenumber of 1479 cm − 1 . At a wavenumber of 1462 cm − 1 no clear peak is recognizable, which also makes a deconvolution of the peaks much more difficult. However, in principle, a slight decrease in crystallinity can also be detected by increasing the irradiation dose, according to the calculation of Schenzel et al. ( 2005 ). Despite the Raman measurements, X-ray diffraction of the (irradiated) pulp samples was carried out in order to get information about their crystalline structure. The diffraction patterns of kraft and cellulose pulp irradiated with 400 kGy show no difference or peak shifts compared to the raw materials, indicating that the structure of the pulps remain unchanged (Fig. 6 a). All patterns exhibit the characteristic diffraction peaks of the cellulose Iß structure at 2θ = 15°, 16.5°, 22.5° and 34.5°, which correspond to the (1–10), (110), (200) and (004) crystallographic planes, respectively (Lee, et al., 2018 ; Wu, et al., 2024 ; French, 2014 ). The crystallinity index (CrI, XRD) was calculated using the Segal method (Segal et al. 1959 ) in order to compare the influence of the EBI treatment on the crystalline structure. Furthermore, the crystalline (86.6–92 ppm) and amorphous (79.8–86.6 ppm) parts were used to determine the crystallinity (CrI, NMR) by NMR experiments (Liitiä et al. 2000 ; Teeäär et al. 1987 ; Schenzel et al. 2005 ). The CrI from XRD diffraction reaches values of 83–85%, and the CrI from NMR experiments shows values in the range of 45–49%, which are in good accordance with studies from Liitiä et al. ( 2000 ). The CrI values show similar trends for both methods, initially rising slightly at an irradiation dose of 100 kGy and then decreasing very slightly up to an irradiation dose of 400 kGy. However, the change in crystallinity and dependence on the irradiation dose up to 400 kGy is extremely small for both kraft pulp and sulfite pulp samples (Fig. 6 b, Table 1 ). Lee et al. ( 2018 ) also report CrI values in the same range (83–85%) at EBI doses up to 500 kGy, only EBI doses above 2000 kGy lead to a decrease below 80%. Other studies also show that there is no significant relationship between irradiation and crystallinity (Schnabel et al. 2015 ; Morin et al. 2004 ; Hwang et al. 2021 ). It is suggested that, in contrast to acid hydrolysis, the chain scission caused by EBI is more random. The EBI attacks both the amorphous and crystalline regions of cellulose because radicals are generated in both. In contrast, acid hydrolysis mainly leads to chain scission in the amorphous region (Hwang et al. 2021 ). Because of the attack on both the crystalline as well as the amorphous regions, it is assumed that the CrI does not change with the EBI doses used in this study. Using different methods, Raman (380/1096 ratio), XRD (Segal method), and NMR, very similar trends were observed, namely that the crystallinity of the pulp samples is nearly unaffected by electron beam irradiation (Fig. 6 b, Table 1 ). In addition, IR measurements were carried out, mainly to investigate the occurrence of carbonyl groups in the pulp samples due to irradiation, because this was shown in some previous studies (Henniges et al. 2013 ; Sarosi et al. 2020 ; Hwang et al. 2021 ). Fig. S1 depicts that there are no obvious changes in the IR spectra of kraft pulp and sulfite pulp irradiated at 400 kGy compared to the raw material, or between the two pulp types itself. Other cellulosic materials also show no change in their IR spectra due to EBI treatment (Kim et al. 2016 ; Wu et al. 2024 ). A prominent band for carbonyl vibrations can be found in the IR spectra of cellulose at wavenumbers near 1720 cm − 1 . We observed an increasing yellowing of the pulps with higher irradiation dose, suggesting that EBI causes carbonyl group formation. However, the band near 1720 cm − 1 cannot be detected in the samples prepared in this study. This indicates that there is no formation of carbonyl bands due to EBI. It is assumed that the occurrence of carbonyl groups, as indicated by EBI, requires a significantly higher irradiation dose, or the amount is so low that it cannot be detected by IR measurements. Lee et al. ( 2018 ) also show just a very small IR peak for cellulose pulp treated with 1000 kGy. The yellowing of the pulps can also result from the formation of furfural due to the degradation of hemicelluloses, which turns yellow by exposition to light and air. Furfural is usually obtained by an acid-catalyzed dehydration of xylan (Binder et al. 2010 ; Wang et al. 2025 ). The bands at 1052 and 1104 cm − 1 arise from C-O-C asymmetric stretching and C-O/C-C stretching at cellulose linkage, and the slight decrease in the intensity of these bands for the irradiated samples indicates glycosidic cleavage through irradiation. The SEM images in Fig. 7 show the morphology of the sulfite pulp samples irradiated at 100, 200 and 400 kGy in comparison to the starting material as well the kraft pulp sample irradiated at 400 kGy. In general, the fiber structure of the pulp remains intact, but an increasing irradiation dose leads to a progressive defibrillation of the fibers and the fibers also appear increasingly flatter and wider. This is consistent with the measured increase in fiber width. Similar observations can be made for the kraft pulp sample irradiated at 400 kGy with a defibrillation of the fibers, as well as significantly wider fibers compared to the starting material. This is in accordance with other studies, where the physical structure also remains fiber-like and no significantly changes can be observed (Lee et al. 2018 ; Wu et al. 2024 ). Figure 7 SEM images of irradiated sulfite pulp and kraft pulp samples at various irradiation dose (1.41 kGy s − 1 , dry sheets) at a magnification of 1,000x. The hemicellulose content and composition of both pulp samples as well as the changes resulting from EBI treatment were analyzed by HPLC measurements (Fig. 6 c). Kraft pulp contains a significantly higher amount of hemicellulose with 13.7% compared to sulfite pulp with 2.1%. The main components in kraft pulp are xylose and mannose. Using an EBI dose of 400 kGy leads to the decomposition of the hemicelluloses to a total amount of 10.6%, while the glucose amount decreases from 82.1% to 72.9%. In contrast, the hemicellulose content decreases very slightly due to irradiation with 200 kGy for the sulfite pulp (1.9%), whereas significant decomposition of glucose can be observed. However, the HPLC measurements show that, even after irradiation, kraft pulps have a high amount of hemicellulose and a composition that differs significantly from those of the sulfite pulps, which influences the properties of the materials as well as their further use as material in the preparation of microfibrillated cellulose. Variation in the irradiation process (atmosphere and dose rate) Besides the irradiation dose, there are many other influencing factors in the EBI process, such as the dose rate, temperature, and humidity, but also the surrounding medium. Additional investigations were therefore carried out at an irradiation dose of 400 kGy to determine the extent, to which the irradiation of dry and wet samples in air or a nitrogen atmosphere influences the both pulp samples. The dose rate was also varied to 0.67 and 1.41 kGy s − 1 (Table 2 ). It was expected that the irradiation of wet samples or in a nitrogen atmosphere leads to an attack in other regions of the cellulose and an altered radical formation compared to the irradiation of dry samples in air. For the intrinsic viscosity, the values of the irradiated samples under different conditions are in the same range, just the wet sulfite pulp shows a slightly greater decrease compared to the other samples. Therefore, the main influencing factor for the degradation of the pulps is the irradiation dose, which is also shown by Hwang et al. ( 2021 ) for dry and wet cellulose papers in the range of 25 to 100 kGy. In contrast, Henniges et al. ( 2013 ) observed at the irradiation dose of 40 and 60 kGy a higher degradation of wet pulps than of untreated dry pulps and lower values for the molar mass. The wet conditions in the irradiation process lead to a higher swelling of the fibers for both pulp samples and, therefore, to an increase of the fiber width compared to the dry or under nitrogen irradiated pulps. This change in the swelling behavior results in a higher WRV for the wet irradiated samples, except for KP_400_50_W. No dependence of the dose rate on the fiber dimensions or the WRV could be determined. The values for the zeta potential are also slightly lower for the wet irradiated samples compared to the dry ones, which is related to a change in the swelling behavior or a decrease in functional groups on the surface. This contradicts the theory that more radicals are produced by wet conditions, leading to a rapid oxidation and a higher carbonyl and carboxyl content in the pulp samples (Henniges et al. 2013 ). Table 2 Properties of kraft pulps and sulfite pulps irradiated with 400 kGy under different conditions KP_400_50_D Intrinsic viscosity [ml g − 1 ] Water retention [%] Zeta potential [mV] Fibre length [mm] Fibre width [µm] CrI [%] (XRD) CrI [%] (NMR) 380/1096 29 67 ± 0.46 -23 ± 0.85 0.82 ± 0.001 29.9 ± 0.05 83.5 45.3 0.38 KP_400_50_W 30 67 ± 0.21 -18 ± 0.25 0.92 ± 0.012 33.2 ± 0.10 77.4 - 0.38 KP_400_50_N2 27 69 ± 0.65 -21 ± 0.30 0.83 ± 0.008 29.2 ± 0.05 82.6 - 0.40 KP_400_5_D 29 61 ± 0.35 -25 ± 0.90 1.08 ± 0.005 29.6 ± 0.05 83.9 - 0.39 KP_400_5_W 31 74 ± 0.36 -20 ± 0.05 0.67 ± 0.009 32.2 ± 0.10 83.5 - 0.37 SP_400_50_D 31 51 ± 0.53 -59 ± 0.20 0.42 ± 0.001 22.9 ± 0.05 83.2 45.4 0.42 SP_400_50_W 25 56 ± 0.23 -53 ± 0.40 0.39 ± 0.001 24.6 ± 0.05 84.2 46.7 0.42 SP_400_50_N2 29 48 ± 0.59 -41 ± 0.00 0.44 ± 0.005 22.1 ± 0.30 83.1 45.5 0.45 SP_400_5_D 33 48 ± 0.22 -61 ± 0.15 0.43 ± 0.002 22.9 ± 0.05 81.5 - 0.42 SP_400_5_W 29 59 ± 2.32 -50 ± 0.90 0.39 ± 0.001 24.8 ± 0.05 83.3 - 0.41 The Raman spectra of dry and wet irradiated samples show no difference neither for kraft pulp nor for sulfite pulp, pointing that the different states (dry or wet) during irradiation in air have no influence on the structure of the material (Fig. 8a). The peaks at a wavenumber of 380 cm − 1 also have a very similar intensity, indicating that there is no decrease in crystallinity (Fig. 8d, e). Some changes can be detected for the samples irradiated under a nitrogen atmosphere. The intensity of the 380 cm − 1 peak is slightly higher for the irradiated pulps under nitrogen compared to the samples irradiated in air. It is assumed that the amorphous regions of cellulose are more likely to be attacked under a nitrogen atmosphere, resulting in a slightly higher 380/1096 ratio. Furthermore, a slightly lower intensity can be determined for the bands at 1337 cm − 1 caused by HCC, HCO, and COH bending, as well as at 1035 and 1057 cm − 1 , which is due to CC and CO stretching vibrations (Fig. 8b, c) (Schenzel and Fischer 2001 ; Wiley and Atalla 1987 ). Figure 8 Raman spectra for kraft pulps and sulfite pulps irradiated with 400 kGy and a dose rate of 1.41 kGy s − 1 under different conditions with a) full spectra and detailed view of b) the band at 1096 cm − 1 and c) the bands between 1300–1400 cm − 1 , as well as the detailed view for the band at 380 cm − 1 for d) kraft pulp and e) sulfite pulp samples. No changes in the IR spectra due to the different atmospheres or dose rate were detected for both pulp types (Fig. S2a) and, as for the irradiation dose, no occurrence of carbonyl groups at a wavenumber around 1720 cm − 1 can be observed. The XRD diffractograms (Fig. S2b) are also very similar, with CrI (XRD) values ranging from 82 to 84%, the CrI values from NMR experiments are in the range of 45–47%. Only the kraft pulp sample KP_400_50_W irradiated as a wet sheet shows a higher reduction in crystallinity and has a CrI value of 77.4%. It is assumed that the radicals lead to a higher chain scission in the crystalline regions of cellulose, which leads to a decreasing crystallinity combined with a higher swelling capacity and thus wider fibres. Figure 9 depicts the SEM images of the kraft pulps and sulfite pulps that were irradiated with 400 kGy under different atmospheres. The defibrillation of the wet irradiated samples appears to be somewhat lower, and the surface of the fibers is slightly smoother, compared to the dry irradiated samples in air. Furthermore, irradiation of the wet samples leads to a higher fiber width because the swelling is promoted. In contrast, the nitrogen atmosphere favors the preservation of the fiber structure, especially in case of sulfite pulp, where the fibers appear less flat than the samples irradiated in air. The defibrillation of the fibers is very similar for the irradiation under air (dry) and nitrogen atmospheres. Figure 9 SEM images of sulfite pulp and kraft pulp samples irradiated under different conditions (dose: 400 kGy, dose rate: 1.41 kGy s − 1 ) at a magnification of 1,000x. Preparation of microfibrillated cellulose Microfibrillated cellulose can be prepared from the irradiated pulps in a relatively simple way using high-pressure homogenization. Before the high-pressure homogenization, the pulps are only stirred and dispersed, but no further chemicals are required. However, it is therefore not possible to prepare MFC with all irradiated pulp samples, as insufficient pre-treatment leads to increased blockages in the high-pressure homogenizer. This is particularly the case with kraft pulp irradiated at ≤ 200 kGy. These tests were discontinued and no further characterization was carried out. It is assumed that sulfite pulp is easier to defibrillate, even at lower irradiation dose, because its fibers already have no primary walls, unlike kraft pulp. A limiting factor in determining whether MFC can be produced from the irradiated pulp in a high-pressure homogenizer without blockages appears to be the fiber length. Since sulfite pulp already has a shorter fiber length, the production is somewhat easier compared to kraft pulp, even at lower irradiation dose. The particle size of the MFC was measured using laser diffraction. Although this method is only partially suitable for measuring fibers, it is a fast and easy way to demonstrate the changes in the MFC, and the values are in a very good accordance with the fiber widths measured with the Fiber tester (Table S1 ). The particle size of the MFC prepared from dry irradiated sulfite pulp decreased from 24.9 µm to 14.9 µm as the irradiation dose increased from 100 to 200 kGy (Table 3 , Fig. 10a). However, increasing the irradiation dose further to 400 kGy leads to an increase in particle size to 28.7 µm, which is presumably related to the formation of numerous agglomerates. The same tendency is also observed for MFCs prepared from the irradiated kraft pulp, which exhibit an increase in particle size from 13.2 µm to 20.9 µm at irradiation dose of 300 and 400 kGy. MFCs prepared from the wet irradiated samples have significantly smaller particle sizes compared to the dry irradiated samples under air. Probably, the structure and properties of the pulps are changed by irradiation under wet conditions in such a way that the fibers are significantly more comminute by dispersing and high-pressure homogenization, and at the same time less prone to agglomerate formation. For the samples under a nitrogen atmosphere, the resulting MFC for kraft pulp is relatively similar to the dry irradiated sample, whereas for sulfite pulp a significantly smaller particle size is detected. Furthermore, the particle size distribution is narrower for all MFCs prepared from kraft pulp, independent of the irradiation conditions, than for the MFCs prepared from sulfite pulp. Raman measurements of the MFCs from sulfite pulp (SP_x_50_D) show a decrease of the intensity of the 380 cm − 1 band when the irradiation dose increases from 200 to 400 kGy, indicating a decrease in crystallinity (Fig. S3). Table 3 Mean particle size (D50) of MFC prepared from irradiated kraft pulp and sulfite pulp samples KP_100_50_D D50 [µm] D50 [µm] - SP_100_50_D 24.9 KP_200_50_D - SP_200_50_D 14.9 KP_400_50_D 20.9 SP_400_50_D 28.7 KP_400_50_W 13.6 SP_400_50_W 4.1 KP_400_50_N2 18.9 SP_400_50_N2 9.8 KP_400_5_D 17.4 SP_400_5_D 55.3 KP_400_5_W 6.4 SP_400_5_W 15.3 Figure 10a) Mean particle size of MFC prepared from SP and KP samples irradiated under different conditions in dependence on the irradiation dose, as well as corresponding particle size distributions of MFC from sulfite pulp samples with different b) irradiation dose and d) irradiation conditions and c) particle size distribution of MFC from kraft pulp samples irradiated at 400 kGy under different conditions. The SEM images in Fig. 11 show the MFC prepared from irradiated sulfite pulp with different irradiation doses. The MFC from the 100 kGy irradiated pulp sample appears more as a net-like mesh, whereby the fibers are still clearly visible and some individual wider fibers are also present. At an irradiation dose of 400 kGy, MFC is produced, in which individual fibers are no longer clearly visible and only shorter particles are present. The aggregation of these particles can be observed in the SEM images, which is consistent with the previously measured higher values of the mean particle size for this sample. If the MFCs are air-dried, an increasing yellowing and a lock of film formation can be observed with higher irradiation dose of the sulfite pulp (Fig. S5). Figure 11 SEM images of MFC prepared from irradiated sulfite pulp samples with different irradiation doses at magnifications of 10,000x and 30,000x. The MFCs produced from kraft pulps and sulfite pulps irradiated at 400 kGy under different conditions (dry, wet, nitrogen atmosphere) exhibit very different morphologies (Fig. 12). Especially the wet irradiated pulps result in MFCs with a significantly more homogeneous surface structure and smaller particles than those produced from the dry irradiated pulps. The MFCs prepared from the irradiated pulps under nitrogen atmosphere also have smaller particles than the dry irradiated samples under air, but the particles are more aggregated than wet irradiated samples. Furthermore, a higher defibrillation can be observed for the MFCs from sulfite pulp compared to kraft pulp. While the morphology of MFCs prepared from kraft pulp is very similar for dry irradiated samples with a change of the dose rate from 1.41 kGy s − 1 to 0.67 kGy s − 1 , significant differences can be observed for wet-irradiated kraft pulp samples. The MFCs from KP_400_5_W have very short particles and no fiber structure can be detected in comparison to KP_400_50_W (Fig. S4). Figure 12 SEM images of MFC prepared from KP and SP samples irradiated with 400 kGy and a dose rate of 1.41 kGy s − 1 under different conditions at magnifications of 1,000x and 30,000x. As expected, the molar mass of kraft pulp is higher than that of sulfite pulp, with values for M N of 368,210 g mol − 1 (KP) and 178,870 g mol − 1 (SP). These difference between the two pulp types is in accordance with previous studies (Duan et al. 2015 ). Irradiation leads to a significant decrease in molar mass due to degradation of the pulp. The M N for irradiated kraft pulp is lower than that of sulfite pulp, which could be related to the higher irradiation dose for KP. The further dispersion and high-pressure homogenization in order to prepare MFC leads only to a slight decrease of the molar mass and a narrower distribution (Fig. 13 ). Dynamic light scattering confirms the results of the particle size measurement with regard to the significant increase in mean particle size for MFC prepared from sulfite pulp when the irradiation dose was increased from 200 to 400 kGy (Table 4 , Fig. S6). As the methods used to determine the particle size differ significantly between laser diffraction and dynamic light scattering, the values can only be compared within each method. Nevertheless, the same trend can be seen in both methods, namely that the particle size of MFC initially decreases with an increasing irradiation dose applied to sulfite pulp, and then increases again, presumably due to the formation of agglomerates. Table 4 Mean particle size (D50) of MFC from kraft pulp and sulfite pulp samples with different irradiation dose measured by dynamic light scattering KP_100_50_D D50 [nm] D50 [nm] - SP_100_50_D 1575.8 KP_200_50_D - SP_200_50_D 876.2 KP_400_50_D 826.7 SP_400_50_D 3873.5 Conclusion In this study, it is demonstrated that electron beam irradiation is a suitable pre-treatment method for pulps in the production of microfibrillated cellulose. As expected, the irradiation dose significantly influences the properties of the pulp, especially the intrinsic viscosity has a strong decrease even at a dose of 100 kGy, which continues at higher doses up to 400 kGy, albeit more slightly. In contrast, no significant change in crystallinity can be detected using Raman, XRD, or NMR measurements. This is because radicals are generated throughout the cellulose by electron irradiation and presumably react in both the crystalline and amorphous areas. The two pulp types differ in fiber length; while the fiber length of the long pulp from the kraft process decreases from irradiation dose of 300 kGy, the fiber length of short pulp from the sulfite process decreases only slightly overall. A change in the atmospheric conditions results in minor changes, such as increased swelling in wet irradiated pulps. It appears that the fiber length is the decisive factor in determining whether direct high-pressure homogenization of the pulp is possible without further pre-treatment to obtain MFC. If the irradiation dose is too high, this results in the formation of agglomerates during the production of MFC, characterized by a larger particle size. Electron beam irradiation proves to be a sustainable effective pre-treatment method, especially since the addition of other chemicals can be avoided entirely. However, finding a suitable irradiation dose for each pulp type remains challenging. Declarations Acknowledgments: The authors would like to thank Prof. Dr. Thomas Heinze (Institute for Organic Chemistry and Macromolecular Chemistry, Center of Excellence for Polysaccharide Research, Friedrich Schiller University, Jena) for the SEC measurements, Dr. Jens Schaller (Thuringian Institute for Textile and Plastic Research, Rudolstadt, Germany) for the dynamic light scattering measurements and Dr. Erica Brendler (TU Bergakademie Freiberg, Institute of Analytical Chemistry, Germany) for the 13C NMR measurements. Furthermore, big thanks go to the Institute of Natural Materials Technology, working group paper technology (TU Dresden, Germany) for the possibility to use the wet lab for WRV and Zeta potential measurements as well as to Annett Völlmar for measuring the fiber dimensions of the pulps. Funding This research was funded by the German Research Foundation (DFG) in the project Cellstor, grant number 511521214 (FI755/16-1, MI945/8-1). Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author contributions Johanna Fischer: Conceptualization, Preparation of MFCs, Methodology, Investigation, Writing – Original draft Michael Thomas Müller: Electron beam irradiation of pulps, Writing – Review and Editing Katrin Thümmler: Conceptualization, Writing – Review and Editing Björn Günther: Methodology – SEM, Writing – Review and Editing Daria Mikhailova: Methodology – XRD, Funding, Writing – Review and Editing Steffen Fischer: Conceptualization, Funding, Supervision, Writing – Review and Editing References Agarwal UP, Reiner RS, Ralph SA (2010) Cellulose I crystallinity determination using FT-Raman spectroscopy: univariate and multivariate methods. Cellulose 17(4):721–733. https://doi.org/10.1007/s10570-010-9420-z Anikushin BM, Lagutin PG, Kanbetova AM, Novikov AA, Vinokurov VA (2022) Zeta Potential of Nanosized Particles of Cellulose as a Function of pH. 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Radiat Phys Chem 173:108872. https://doi.org/10.1016/j.radphyschem.2020.108872 Nedon W, Schwarz W, Rögner FH, Portillo Casado J, Kubusch J, Fischer S, Free M, Mensch A, Thümmler K, Anders M, Böhme N, Tehsmer V, Schuhmann K (2021a) Verfahren zum Herstellen eines Nanocellulosepartikel enthaltenden Verbundwerkstoffes. DE102020116043.7. Nedon W, Schwarz W, Rögner FH, Portillo Casado J, Kubusch J, Fischer S, Freese M, Mensch A, Thümmler K, Anders M, Böhme N, Tehsmer V, Schuhmann K (2021b) Verfahren zum Restaurieren von einem Papiersubstrat. DE102020116044.5. Osong SH, Norgren S, Engstrand P (2016) Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose, and applications relating to papermaking: a review. Cellulose 23:93–123. https://doi.org/10.1007/s10570-015-0798-5 Phanthong P, Reubroycharoen P, Hao X, Xu G, Abudula A, Guan G (2018) Nanocellulose: Extraction and application. Carbon Resour Convers 1(1):32–43. https://doi.org/10.1016/j.crcon.2018.05.004 Saeman JF, Millett MA, Lawton EJ (1952) Effect of High-Energy Cathode Rays on Cellulose. Ind Eng Chem 44(12):2848–2852. https://doi.org/10.1021/ie50516a027 Santos RB, Jameel H, Chang HM, Hart PW (2012) Kinetics of Hardwood Carbohydrate Degradation during Kraft Pulp Cooking. Ind Eng Chem Res 51(38):12192–12198. https://doi.org/10.1021/ie301071n Sarosi OP, Bischof RH, Potthast A (2020) Tailoring Pulp Cellulose with Electron Beam Irradiation: Effects of Lignin and Hemicellulose. ACS Sustainable Chem Eng 8(18):7235–7243. https://doi.org/10.1021/acssuschemeng.0c02165 Schenzel K, Fischer S (2001) NIR FT Raman spectroscopy - a rapid analytical tool for detecting the transformation of cellulose polymorphs. Cellulose 8:49–57. https://doi.org/10.1023/A:1016616920539 Schenzel K, Fischer S, Brendler E (2005) New method for determining the degree of cellulose I crystallinity by means of FT Raman spectroscopy. Cellulose 12:223–231. https://doi.org/10.1007/s10570-004-3885-6 Schnabel T, Huber H, Grünewald TA, Petutschnigg A (2015) Changes in mechanical and chemical wood properties by electron beam irradiation. Appl Surf Sci 332,:704–709. https://doi.org/10.1016/j.apsusc.2015.01.142 Schroeder LR, Gentile VM, Atalla RH (1986) Nondegradative Preparation of Amorphous Cellulose. J Wood Chem Technol 6(1):1–14. https://doi.org/10.1080/02773818608085213 Segal L, Creely JJ, Martin AE, Conrad, CM (1959) An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose Using the X-Ray Diffractometer. Text Res J 29(10):786–794. https://doi.org/10.1177/004051755902901003 Siró I, Plackett D (2010) Microfibrillated cellulose and new nanocomposite materials: a review. Cellulose 17:459–494. https://doi.org/10.1007/s10570-010-9405-y Sixta, H (2006) Handbook of Pulp. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Stana-Kleinschek K, Kreze T, Ribitsch V, Strnad S (2001) Reactivity and electrokinetical properties of different types of regenerated cellulose fibres. Colloids Surf A: Physicochem Eng Asp 195(1–3):275–284. https://doi.org/10.1016/S0927-7757(01)00852-4 Stenstad P, Andresen M, Tanem BS, Stenius P (2008) Chemical surface modifications of microfibrillated cellulose. Cellulose 15:35–45. https://doi.org/10.1007/s10570-007-9143-y Sun Y, Chmielewski AG (2017) Applications of ionizing radiation in materials processing. Institute of Nuclear Chemistry and Technology, Warsaw TAPPI (1997) TAPPI T 204 cm-97: solvent extraction of wood and pulp. Teeäär R, Serimaa R, Paakkarl T (1987) Crystallinity of cellulose, as determined by CP/MAS NMR and XRD methods. Polym Bull 17:231–237. https://doi.org/10.1007/BF00285355 Turbak AF, Snyder FW, Sandberg KR (1983) Microfibrillated Cellulose, a new Cellulose Product: Properties, Uses, and Commercial Potential. J Appl Polym Sci: Appl Polym Symp 37:815–827. Van Hai L, Seo YB (2016) Effects of electron beam treatment on cotton linter for the preparation of nanofibrillated cellulose. J Korea TAPPI, 48(2):68–74. https://doi.org/10.7584/ktappi.2016.48.2.068 Van Hai L, Seo YB (2017) Characterization of cellulose nanocrystal obtained from electron beam treated cellulose fiber. Nordic Pulp Pap Res J 32(2):170–178. https://doi.org/10.3183/npprj-2017-32-02-p170-178 Vanhatalo K, Lundin T, Koskimäki A, Lillandt M, Dahl O (2016) Microcrystalline cellulose property-structure effects in high-pressure fluidization: microfibril characteristics. J Mater Sci 51:6019–6034. https://doi.org/10.1007/s10853-016-9907-6 Wang Y, Li M, Wang Z, Liu S, O’Young L (2025) Furfural production: A review on reaction mechanism and conventional production process. Ind Crops Prod 230:121103. https://doi.org/10.1016/j.indcrop.2025.121103 Wiley JH, Atalla RH (1987) Band assignments in the Raman Spectra of Cellulose. Carbohydr Res 160:113–129. https://doi.org/10.1016/0008-6215(87)80306-3 Wu Q, Ding C, Wang B, Rong L, Mao Z, Feng X (2024) Green, chemical-free, and high-yielding extraction of nanocellulose from waste cotton fabric enabled by electron beam irradiation. Int J Biol Macromol 267(2):131461. https://doi.org/10.1016/j.ijbiomac.2024.131461 Young RA (1994) Comparison of the properties of chemical cellulose pulps. Cellulose 1:107–130. https://doi.org/10.1007/BF00819662 Zhang X, Xi C, Guo S, Yan M, Lu Y, Sun Z, Ge X, Shen H, Ospankulova G, Muratkhan M, Kh KZ, Hu Y, Li W (2024) Electron beam pre-irradiation enhances substitution degree, and physicochemical and functional properties of caboxymethyl peanut shell nanocellulose. Ind Crops Prod 209:118035. https://doi.org/10.1016/j.indcrop.2024.118035 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9028732","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":601239343,"identity":"be6f9de0-aafb-4f6f-952b-094c95edeb62","order_by":0,"name":"Johanna Fischer","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABNElEQVRIie2RMUvDQBSALxw0yzuzKhH9C1cCcbA0f+Uk0ClDxaVgwUDhuqR7C/kRHR0crgSS5ehcEKxdOsUpY6F6TVTERLo63Lfcu8d9vPfuIaTR/EOMEKrAHCGE1QnW4VYmxVfwhwJJpZyf8SPKdxJEpXRoekTB48miuH3sIjDNTdEfvICzjih6e+p4J9lEoHxQbyxa+vZM+ggwOPZU3oGbAjXibe9mJpfMiGVdmQbUJhwjD0MLE84OytUORMLoKqAq06Q4O8IfVBVzi8megcOBYhDvHl3nStk3Ka6qkigFuZiEDGirVIQxX6mAhA2zSPea8AzKWSBlcJr2+kYsfDVLQBdxWlPa48h5Jvz+AqxsU8CQedYomaNcdNWPyfZrPqwrn4UbV1at5jeXzU81Go1G84MPKshgoTUY450AAAAASUVORK5CYII=","orcid":"","institution":"TU Dresden","correspondingAuthor":true,"prefix":"","firstName":"Johanna","middleName":"","lastName":"Fischer","suffix":""},{"id":601239344,"identity":"7b6584a5-71c4-43cb-8a96-030d8aa6b3d9","order_by":1,"name":"Michael Thomas Müller","email":"","orcid":"","institution":"Leibniz Institute of Polymer Research","correspondingAuthor":false,"prefix":"","firstName":"Michael","middleName":"Thomas","lastName":"Müller","suffix":""},{"id":601239345,"identity":"4691d585-1024-4817-bc27-7f9657aed7a1","order_by":2,"name":"Katrin Thümmler","email":"","orcid":"","institution":"TU Dresden","correspondingAuthor":false,"prefix":"","firstName":"Katrin","middleName":"","lastName":"Thümmler","suffix":""},{"id":601239346,"identity":"e930c918-356b-43ce-bd56-5ea8c8ff58ea","order_by":3,"name":"Björn Günther","email":"","orcid":"","institution":"TU Dresden","correspondingAuthor":false,"prefix":"","firstName":"Björn","middleName":"","lastName":"Günther","suffix":""},{"id":601239347,"identity":"3411ffd9-f192-42a4-8f7b-f7f37a00aff6","order_by":4,"name":"Daria Mikhailova","email":"","orcid":"","institution":"Karlsruhe Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Daria","middleName":"","lastName":"Mikhailova","suffix":""},{"id":601239348,"identity":"8efc5de5-bc5d-4514-a5e9-507b626de6a4","order_by":5,"name":"Steffen Fischer","email":"","orcid":"","institution":"TU Dresden","correspondingAuthor":false,"prefix":"","firstName":"Steffen","middleName":"","lastName":"Fischer","suffix":""}],"badges":[],"createdAt":"2026-03-04 09:54:58","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9028732/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9028732/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105698309,"identity":"b63976f4-6fa0-4e36-95a3-4e6f72112f53","added_by":"auto","created_at":"2026-03-30 04:55:49","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":170637,"visible":true,"origin":"","legend":"\u003cp\u003eScheme for the preparation of microfibrillated cellulose. Created with BioRender.com.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/fe5ad649980bee9aa3d20b66.png"},{"id":105698277,"identity":"bf8797c5-2aff-408c-9862-03ed57b4510e","added_by":"auto","created_at":"2026-03-30 04:55:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":545499,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the both pulp samples (kraft pulp and sulfite pulp) at magnifications of 200x, 1,000x and 5,000x.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/67791eb9e33f3b57ad01131a.png"},{"id":105698274,"identity":"d25cd315-a087-4fdd-9ffd-412372d7eaa0","added_by":"auto","created_at":"2026-03-30 04:55:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":125274,"visible":true,"origin":"","legend":"\u003cp\u003ea) Intrinsic viscosity, b) Fiber Length and c) Fiber Width of the raw material and irradiated kraft pulp and sulfite pulp in dependence on the electron beam irradiation dose (dose rate 1.41\u0026nbsp;kGy\u0026nbsp;s\u003csup\u003e-1\u003c/sup\u003e, dry sheets).\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/f3576a123899e67ca7674208.png"},{"id":105698284,"identity":"151b2ee8-71ec-442f-aae4-6713eb8463bf","added_by":"auto","created_at":"2026-03-30 04:55:40","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":138593,"visible":true,"origin":"","legend":"\u003cp\u003ea) Water retention capacity and b) Zeta potential of raw materials and irradiated kraft pulp and sulfite pulps in dependence on the electron beam irradiation dose (dose rate 1.41\u0026nbsp;kGy\u0026nbsp;s\u003csup\u003e-1\u003c/sup\u003e, dry sheets).\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/fe7564f72e5aebf7fdb19558.png"},{"id":105729284,"identity":"ba49aaa7-cdb6-40e1-9dc4-c48dde448f0d","added_by":"auto","created_at":"2026-03-30 11:14:09","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":117157,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra for raw materials and irradiated kraft pulps and sulfite pulps with a) full spectra and detailed view of a) the band at 380\u0026nbsp;cm\u003csup\u003e-1\u003c/sup\u003e and b) the bands at 1462\u0026nbsp;cm\u003csup\u003e-1\u003c/sup\u003e and 1481\u0026nbsp;cm\u003csup\u003e-1\u003c/sup\u003e\u003cem\u003e.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/66b5c2649c9a8f7877244867.png"},{"id":105698311,"identity":"19aa5712-271f-45bf-b240-f580ed130259","added_by":"auto","created_at":"2026-03-30 04:55:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":160655,"visible":true,"origin":"","legend":"\u003cp\u003ea) X-ray diffraction patterns, b) comparison of the crystallinity index (CrI) from XRD measurements and 380/1096 ratio from Raman and c) HPLC measurements for KP and SP at different irradiation dose.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/20d1d8a005a64474e00e74dd.png"},{"id":105698290,"identity":"01d47975-f1d5-44dc-ae40-eaa46f059a9e","added_by":"auto","created_at":"2026-03-30 04:55:45","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":855656,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of irradiated sulfite pulp and kraft pulp samples at various irradiation dose (1.41\u0026nbsp;kGy\u0026nbsp;s\u003csup\u003e-1\u003c/sup\u003e, dry sheets) at a magnification of 1,000x.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/4c1e043acf7575f53518198f.png"},{"id":105698283,"identity":"823ee60d-5443-4481-9cc2-d5fc4543fbb6","added_by":"auto","created_at":"2026-03-30 04:55:40","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":242741,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra for kraft pulps and sulfite pulps irradiated with 400\u0026nbsp;kGy and a dose rate of 1.41\u0026nbsp;kGy\u0026nbsp;s\u003csup\u003e-1\u003c/sup\u003e under different conditions with a) full spectra and detailed view of b) the band at 1096\u0026nbsp;cm\u003csup\u003e-1\u003c/sup\u003e and c) the bands between 1300\u0026nbsp;–\u0026nbsp;1400\u0026nbsp;cm\u003csup\u003e-1\u003c/sup\u003e, as well as the detailed view for the band at 380\u0026nbsp;cm\u003csup\u003e-1\u003c/sup\u003e for d) kraft pulp and e) sulfite pulp samples.\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/1c31b715b573bbd04515682c.png"},{"id":105698259,"identity":"06e8a6bf-8bcc-4ca7-896c-3e4ac612989f","added_by":"auto","created_at":"2026-03-30 04:55:30","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":563835,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of sulfite pulp and kraft pulp samples irradiated under different conditions (dose: 400\u0026nbsp;kGy, dose rate: 1.41\u0026nbsp;kGy\u0026nbsp;s\u003csup\u003e-1\u003c/sup\u003e) at a magnification of 1,000x.\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/91b2da4cc683a396457a4093.png"},{"id":105698236,"identity":"c2e59d0f-8c33-4cd7-ba1a-10ed2dd6d425","added_by":"auto","created_at":"2026-03-30 04:55:19","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":293644,"visible":true,"origin":"","legend":"\u003cp\u003ea) Mean particle size of MFC prepared from SP and KP samples irradiated under different conditions in dependence on the irradiation dose, as well as corresponding particle size distributions of MFC from sulfite pulp samples with different b) irradiation dose and d) irradiation conditions and c) particle size distribution of MFC from kraft pulp samples irradiated at 400 kGy under different conditions.\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/93b919a6547c6f2dfefd185c.png"},{"id":105698257,"identity":"28f6a23d-b6e4-4426-9cc3-97a7a200035a","added_by":"auto","created_at":"2026-03-30 04:55:28","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":602776,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of MFC prepared from irradiated sulfite pulp samples with different irradiation doses at magnifications of 10,000x and 30,000x.\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/4db1726735f831be7a549266.png"},{"id":105698247,"identity":"e90d7823-fd1f-4f6f-bb6c-370ca8c8c7ff","added_by":"auto","created_at":"2026-03-30 04:55:25","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":726999,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of MFC prepared from KP and SP samples irradiated with 400\u0026nbsp;kGy and a dose rate of 1.41\u0026nbsp;kGy\u0026nbsp;s\u003csup\u003e-1\u003c/sup\u003e under different conditions at magnifications of 1,000x and 30,000x.\u003c/p\u003e","description":"","filename":"image12.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/10f4b4bd34551388761062d3.png"},{"id":105698252,"identity":"67d8907a-1312-413e-a55e-5d32f16f47e1","added_by":"auto","created_at":"2026-03-30 04:55:26","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":157543,"visible":true,"origin":"","legend":"\u003cp\u003eSEC curves of a) kraft pulp and b) sulfite pulp, the irradiated samples and the resulting MFCs as well as the c) Number (Mn) average molecular weights.\u003c/p\u003e","description":"","filename":"image13.png","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/92504c2eac7bcc3d35c9fbde.png"},{"id":106959194,"identity":"02a759bd-0633-4662-9ccf-4beed383e4b1","added_by":"auto","created_at":"2026-04-15 08:54:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5996161,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/58d55655-a67d-420a-ab90-06ca334fdf29.pdf"},{"id":105698248,"identity":"ba6e5a0d-f7c1-4e5c-b8fe-704fd519b712","added_by":"auto","created_at":"2026-03-30 04:55:25","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2651385,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9028732/v1/0e27e4601301dc6491b845fb.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Microfibrillated cellulose prepared by electron beam irradiated pre-treatment – a comparison of various influencing factors with regard to material and process","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThere is a growing demand in the daily life for the application of renewable, biodegradable, environmentally friendly, and recyclable materials that are highly abundant. In this context, microfibrillated cellulose (MFC) is attracting increasing attention in a wide field of applications due to its attractive properties with regard to a high strength, low weight, dimensional stability, high optical transparency and non-toxicity. Currently, MFC is mostly used in paper and paperboard applications as a strength additive or for surface coatings, and in food applications for barrier coatings. However, it can also be used for medical, cosmetic and pharmaceutical applications (Osong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Stenstad et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Sir\u0026oacute; and Plackett \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMicrofibrillated cellulose, alternatively referred to as nanofibrillated cellulose, consists of aggregates of cellulose microfibrils with a thickness in the range of 20\u0026ndash;60 nm and a length of several tens of micrometers (Lavoine et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Sir\u0026oacute; and Plackett \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Phanthong et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Another type of nanocellulose is cellulose nanocrystals (CNC), also known as cellulose nanowhiskers, which have a diameter of 2\u0026ndash;20 nm and a length of 100\u0026ndash;500 nm (Phanthong et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Sir\u0026oacute; and Plackett \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Because CNCs are extracted from cellulose chains through acid hydrolysis, they have mainly crystalline regions. In contrast, MFC consists of both amorphous and crystalline parts, and usually forms rigid, web-like networks (Sir\u0026oacute; and Plackett \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Lavoine et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Osong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, Phanthong et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). As sources for producing MFC, wood pulp is mainly used, but agricultural crops and their by-products, as well as bacterial cellulose, are also viable sources (Sir\u0026oacute; and Plackett \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). In 1983, Herrick et al. (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1983\u003c/span\u003e) and Turbak et al. (\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1983\u003c/span\u003e) first described a method for producing MFC whereby a dilute cellulosic wood pulp-water suspension was passed through a mechanical homogenizer under high pressure. Presently, the predominant method of MFC production involves mechanical treatment and high-pressure homogenization. For the high-pressure homogenization a microfluidizer equipped with different chambers is used, where high shear rates promote the formation of very thin and uniformly sized cellulose fibers. Other methods of producing MFC include grinding, cryocrushing and electrospinning. All methods for the fibrillation of cellulose fibers to microfibrillated cellulose require intensive mechanical treatment and, consequently, result in high energy consumption. Therefore, pre-treatments are recommended to reduce the energy input. Alkaline, enzymatic, TEMPO-mediated oxidation and carboxymethylation pre-treatments are proposed (Sir\u0026oacute; and Plackett \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Lavoine et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Vanhatalo et al. \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Coura et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWood pulp is predominantly used for the production of MFC, which can have a wide range of properties depending on the pulping process and the type of wood used. The kraft process is mainly utilized for producing pulp, which is characterized by its high strength in comparison to alternative chemical pulping methods (Santos et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Young \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). In contrast, sulfite pulp is more readily bleached and refined compared to kraft pulp, and the unbleached sulfite pulp is significantly brighter. In addition, sulfite pulps have been shown to possess a higher swelling capacity and a broader molecular weight distribution (Sixta \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Duan et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Young \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). Another major difference between the pulps derived from the acid sulfite pulping and the kraft pulping processes is the destruction of the primary cell wall. While acid sulfite pulping completely destroys the primary cell wall, kraft pulping leaves it largely intact, which can lead to significant differences in subsequent refining (Sixta \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Duan et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In addition to the type of chemical pulping, the raw material used is also very decisive for the properties of the pulp. For instance, the fibers of softwood are significantly longer than those of hardwood in the kraft process (Lapierre et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eElectron beam irradiation (EBI) can improve the physical and chemical properties of materials and can be used for many different purposes, including cross-linking of polymers, degradation of materials, polymer backbone modification, surface functionalization, and sterilization of medical equipment (Krieg et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Huang et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Leopold et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; M\u0026uuml;ller et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Davila et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, thermally generated electrons were accelerated by an electromagnetic field and guided along the beam tube to modify the samples. The advantages of electron beam irradiation for modification, particular of biomass, are that the method is completely chemical-free, has a short process time, and can be carried out under convenient conditions (room temperature, atmosphere, ordinary pressure) (Sarosi et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Choi et al, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Lee et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Furthermore, the parameters of the radical-induced chemical reactions can be precisely controlled by adjusting beam parameters such as beam current and energy. The effects of ionizing radiation on cellulose and other polysaccharides are studied in literature (Ershov \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Charlesby \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1955\u003c/span\u003e; Ershov and Klimentov \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1984\u003c/span\u003e; Sun and Chmielewski \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). A high-energy electron treatment of cellulose results in the generation of polymer chain radicals, which are formed along the cellulose backbone induced by ionization and excitation. Alternatively, radicals may be generated via water radiolysis, followed by subsequent radical transfer to the polymer backbone (Sun and Chmielewski \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The polymer radicals react further predominantly via chain scission and depolymerization. Such chain scission reactions alter the polymer structure and consequently change the properties of cellulose with regard to crystallinity, chemical reactivity, mechanical behavior, surface energy, molar mass, and solubility (Charlesby \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1955\u003c/span\u003e; Ershov \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Furthermore, electron beam irradiation can introduce oxidized groups, particularly carbonyl and carboxyl groups, whereby the proportion increases with a higher EBI dose (Saeman et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e1952\u003c/span\u003e; Henniges et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Sarosi et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Fischer et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Ershov and Klimentov \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). Radicals at C1 and C4 positions cleave the 1,4-glycosidic bond, which leads to chain scission and the formation of aldehyde groups (Sun and Chmielewski \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The radicals localized at C2, C3 and C5 positions lead to the formation of carbonyl groups, without causing scission reactions (Ershov \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). At very low irradiation doses, also cross-linking of cellulose can occur instead of chain scission (Choi et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Lee et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In addition to the EBI dose, other factors play a significant role upon the electron beam treatment of pulp including moisture content, temperature, working atmosphere, and the structure and composition of the starting material (Sarosi et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, there have been no comprehensive studies on the effects of EBI on different pulp types as well as on pulp irradiation of wet material or irradiation under nitrogen atmosphere.\u003c/p\u003e \u003cp\u003eUntil now, only a few studies have used electron beam irradiation as a pre-treatment for the preparation of cellulosic nanomaterials like microfibrillated cellulose or cellulose nanocrystals. Lee et al. (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) employed EBI as a pre-treatment for the preparation of CNC from dissolving softwood pulp, where irradiation doses\u0026thinsp;\u0026gt;\u0026thinsp;500 kGy were applied for the direct production of CNC after irradiation. At lower irradiation doses, the preparation of CNC is carried out by alkali treatment. Nedon et al. (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e) also proposed electron beam irradiation as a pre-treatment for producing nanocellulose particles to be used for the restoration of paper substrates (Nedon et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021b\u003c/span\u003e). Wu et al. (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) investigated the suitability of waste cotton fabrics as starting material for the production of cellulose nanorods using EBI pre-treatment. EBI has also been utilized as a pre-treatment process followed by acid hydrolysis in order to produce nanocellulose from various starting materials, such as kenaf (Kim et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), cotton linter (Hai and Seo \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), and bleached softwood kraft pulp (Hai and Seo \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis study investigates how the properties of cellulose are affected by electron beam irradiation, with the aim of making targeted adjustments. Therefore, different types of pulp (kraft pulp vs. sulfite pulp) were used, and the irradiation conditions were varied in terms of irradiation dose ranging from 100\u0026ndash;400 kGy, dose rate, and atmosphere. The irradiated pulps are comprehensively characterized, in particular regarding to degradation (intrinsic viscosity), crystallinity (Raman spectroscopy and X-ray diffraction), morphology (Scanning Electron Microscopy), swelling behavior (Water Retention Value) and changes in fiber dimensions. These pre-treated, irradiated pulps were used to prepare microfibrillated cellulose by high-pressure homogenization. This two-step preparation of microfibrillated cellulose (Fig.\u0026nbsp;1) is a suitable and sustainable way without adding any further chemicals into the process. Furthermore, it enables easy adjustment of the properties of the resulting MFCs.\u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"6\" name=\"Grafik 6\"\u003e\u003c/div\u003eFigure\u0026nbsp;1 Scheme for the preparation of microfibrillated cellulose. Created with BioRender.com.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eTwo different pulps prepared by kraft and sulfite process were used in this study. Northern Bleached Softwood Kraft pulp (KP) prepared from spruce and pine was provided by Mercer, Stendal and Bleached Hardwood Sulfite pulp (SP) prepared from beech by Lenzing, Austria.\u003c/p\u003e \u003cp\u003eThe chemicals used for the analysis were purchased from VWR or Carl Roth and were used as received. For all washing and dilution steps, deionized water was used.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eElectron beam irradiation (EBI)\u003c/h3\u003e\n\u003cp\u003eThe pulp was cut into samples with dimensions of approximately 21 x 30 cm, which were then irradiated using an electron accelerator ELV-2 from Budker Institute of Nuclear Physics, Novosibirsk (Dorschner et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). The irradiation was carried out with a constant electron energy (1 MeV) and electron current (2\u0026ndash;4 mA). Irradiation total doses between 100\u0026thinsp;\u0026plusmn;\u0026thinsp;10 and 400\u0026thinsp;\u0026plusmn;\u0026thinsp;40 kGy were applied at dose rates of 0.67 and 1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which results in single-pass irradiation field doses of 5 and 50 kGy, respectively. For comparison, both dry (D) and wet (W) sheets were irradiated at different doses under ambient air. The wet sheets were moistened to their maximum water absorption capacity. In addition, each pulp sample was irradiated in a nitrogen atmosphere (N\u003csub\u003e2\u003c/sub\u003e) at a dose of 400\u0026thinsp;\u0026plusmn;\u0026thinsp;40 kGy. 24 h after irradiation, the cellulose samples were immersed in water for 5 min to guench the existing radicals.\u003c/p\u003e \u003cp\u003eThe labelling of the samples is done in the following way: \u0026ldquo;\u003cem\u003epulp\u003c/em\u003e_\u003cem\u003edose\u003c/em\u003e_\u003cem\u003edose rate\u003c/em\u003e_\u003cem\u003eatmosphere\u0026rdquo;\u003c/em\u003e, e.g., KP_400_50_D is a dry kraft pulp treated with 400 kGy at a single-pass irradiation dose of 50 kGy in an air atmosphere.\u003c/p\u003e\n\u003ch3\u003eHigh-pressure homogenization\u003c/h3\u003e\n\u003cp\u003eFirst, 30 g irradiated pulp was added to 1 L water and stirred for 30 min. Afterwards the suspension was dispersed with an Ultraturrax at 16,000 rpm for 90 min. The high-pressure homogenization was carried out using a 200-\u0026micro;m-chamber at a pressure of 360 bar and a 100-\u0026micro;m-chamber at a pressure of 1,000 bar for one hour each.\u003c/p\u003e\n\u003ch3\u003eCharacterizations\u003c/h3\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eChemical composition\u003c/h2\u003e \u003cp\u003eFor the analysis of the chemical composition of the pulps, the extract (TAPPI \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e1997\u003c/span\u003e), cellulose (K\u0026uuml;rschner and Hoffer \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1931\u003c/span\u003e), and Klason lignin content was determined. A detailed description of the methods can be found in G\u0026uuml;nther et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eHigh-Pressure Liquid Chromatography (HPLC)\u003c/h2\u003e \u003cp\u003ePrior to HPLC measurements, a hydrolysis of polysaccharides to monosaccharides with trifluoroacetic acid was carried out for the (irradiated) pulps (Fengel et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1978\u003c/span\u003e). In order to determine the hemicellulose composition, an HPLC analysis was performed on a HPLC unit Azura (Knauer) running at 80\u0026deg;C with a flow rate of 0.3 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (H\u003csub\u003e2\u003c/sub\u003eO) using Agilent MetaCarb87P columns and a RID2.1L detector (Knauer). Glucose, arabinose, xylose, and galactose were used as calibration standards, and calculations were performed using the ClarityChrom software.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eIntrinsic viscosity\u003c/h3\u003e\n\u003cp\u003eDetermination of the intrinsic viscosity was carried out based on DIN EN 60450 (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The pulp samples were defibrillated in 25 ml water using a shaking device and afterwards 25 ml of CUEN solution were added. The specific viscosities (ν\u003csub\u003es\u003c/sub\u003e) of the samples were measured with an Ubbelohde viscometer by the outflow time of the CUEN pulp solution (t\u003csub\u003es\u003c/sub\u003e) and the outflow time of the CUEN blank solution (t\u003csub\u003eB\u003c/sub\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${v}_{s}=\\frac{{t}_{s}-{t}_{B}}{{t}_{s}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe intrinsic viscosity v was calculated from the specific viscosities v\u003csub\u003es\u003c/sub\u003e, the concentration c and the Martin\u0026acute;s constant k (k\u0026thinsp;=\u0026thinsp;0.14) with the empirical formula according to Martin (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1951\u003c/span\u003e):\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${v}_{s}=\\left[v\\right]\\text{*}{c}^{k\\left[v\\right]\\text{*}c}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\n\u003ch3\u003eWater retention value (WRV)\u003c/h3\u003e\n\u003cp\u003eThe WRV of the (irradiated) pulps was determined according to ISO 23714 (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), and the fiber dimensions were measured using an L\u0026amp;W Fiber Tester following ISO 16065-1 (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Zeta potential measurements were performed to determine the surface charge of the (irradiated) pulps using a SZP 06 (M\u0026uuml;tek GmbH).\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eScanning electron microscopy (SEM)\u003c/h2\u003e \u003cp\u003eSEM images of the (irradiated) pulps and the resulting microfibrillated cellulose were recorded using a FEI Quanta FEG 650 microscope at an accelerating voltage of 5 kV using a SE detector. All samples were sputter-coated with gold (JEOL JFC 1100E ion sputter) to minimize charging effects.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eRaman spectroscopy\u003c/h2\u003e \u003cp\u003eRaman measurements were performed using a MultiRam (Bruker Optik GmbH) with a laser power of 100 mW for microfibrillated cellulose and 300 mW for the raw material and (irradiated) pulp, at a wavelength of 1064 nm. The spectra were recorded over the range of 3500\u0026ndash;5 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with 100 scans, using an operating spectral resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The spectra were normalized and a baseline correction was conducted using the operating spectroscopy software OPUS Ver. 6.5 (Bruker).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eX-ray diffraction (XRD)\u003c/h2\u003e \u003cp\u003eThe X-ray diffraction patterns of the (irradiated) pulps were carried out at a STOE STADI P powder diffractometer using Cu Kα\u003csub\u003e1\u003c/sub\u003e radiation of 1.54056 \u0026Aring; wavelength, a scan range between 5\u0026deg; \u0026lt; 2θ\u0026thinsp;\u0026lt;\u0026thinsp;100\u0026deg;, and a step size of Δ2θ\u0026thinsp;=\u0026thinsp;0.01\u0026deg;. The crystallinity index (CrI) was calculated as follows by the method of Segal et al. (\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1959\u003c/span\u003e):\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$CrI=\\frac{{I}_{002}-{I}_{am}}{{I}_{002}}\\text{*}100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere I\u003csub\u003e002\u003c/sub\u003e is the maximum peak intensity of the 002 Bragg reflection at 2θ\u0026thinsp;=\u0026thinsp;22.5\u0026deg;, while I\u003csub\u003eam\u003c/sub\u003e is the peak intensity of the amorphous region at 2θ\u0026thinsp;=\u0026thinsp;18\u0026ndash;19\u0026deg;.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eFourier transform infrared spectroscopy (FTIR)\u003c/h2\u003e \u003cp\u003eFTIR measurements were performed at a FTIR spectrometer Tensor27 (Bruker Optik GmbH). For each measurement, a spectrum with 32 scans and a resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was recorded over the range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cem\u003e13C NMR measurements\u003c/em\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003e13\u003c/sup\u003eC solid state NMR measurements were carried out at 100.6 MHz on a 400 MHz Bruker AVIII HD WB spectrometer equipped with a CP/MAS probe using 4 mm ZrO\u003csub\u003e2\u003c/sub\u003e rotors at 10 kHz spinning speed. A contact time of 1 ms with an 80% ramp on the \u003csup\u003e1\u003c/sup\u003eH channel was applied for CP, experiment recycle delays were 3 s, the acquisition time 35 ms, and a spinal64 decoupling sequence was applied during acquisition. 10000 scans were accumulated. The chemical shift was referenced externally using the CH\u003csub\u003e2\u003c/sub\u003e-group signal of adamantane (38.5 ppm with respect to TMS\u0026thinsp;=\u0026thinsp;0 ppm). To calculate the crystallinity of the (irradiated) pulps, the crystalline part at the C4 atom was integrated in the range from 92 -86.6 ppm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eParticle size measurements\u003c/h2\u003e \u003cp\u003eThe particle size distributions of the microfibrillated cellulose after dispersing as well as after high-pressure homogenization in different chambers (200 \u0026micro;m and 100 \u0026micro;m) were determined using a laser diffraction particle analyzer Mastersizer 3000 (Malvern), the data were analyzed using the Mie Model.\u003c/p\u003e \u003cp\u003eDynamic light scattering measurements were carried out on a Horiba LB-550 in the size range of 0.001 to 6 \u0026micro;m.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eSize exclusion chromatography (SEC)\u003c/h2\u003e \u003cp\u003eFor determining the molar mass of the pulp, irradiated pulp and MFC samples, SEC was used at 30\u0026deg;C with a setup containing a LC-10AD VP pump, two columns (PSS SDV guard, PSS SDV lin M), UV-vis and refractive index detectors. As eluent, THF with a flow rate of 1 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was used. The samples have to be carbanilated before the SEC measurements to make them THF-soluble.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization of the raw material\u003c/h2\u003e \u003cp\u003eFor the irradiation experiments, kraft pulp (KP) and sulfite pulp (SP) were used in order to investigate the influence of the EBI treatment on the different kind of pulps. Both pulps are almost free of lignin, with Klason lignin amounts\u0026thinsp;\u0026lt;\u0026thinsp;0.05%, and have an extractive content of about 0.4%. The cellulose content of kraft pulp is 93.4%, while that of sulfite pulp is 94.5%. HPLC measurements show a very high proportion of glucose within the both samples of 82% in kraft pulp and 97% in sulfite pulp. Kraft pulp contains a higher proportion of hemicellulose consisting of 7.5% xylose, 5.8% of mannose, 0.4% arabinose and traces of galactose, whereas in sulfite pulp only about 1.4% xylan and 0.6% mannose can be detected.\u003c/p\u003e \u003cp\u003eThe M\u003csub\u003eN\u003c/sub\u003e value of the kraft pulp sample is 368,210 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Sulfite pulp shows a smaller M\u003csub\u003eN\u003c/sub\u003e of 178,870 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, but has a broader distribution, which indicates higher polydispersity. The differences of the molecular mass result mainly from the different pulping processes (Duan et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe SEM images in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e show the morphological fiber structures of both pulp samples. While the kraft pulp fibers have a relatively flat and straight shape, those of sulfite pulp have a tube-like form. Further differences between the two pulps can be determined in their surface structures. The fibers of kraft pulp have a predominantly smooth surface with occasional peeling of the fibers, whereas the surface of sulfite pulp is rather rough due to defibrillation and peeling of the fibers. The measured average fiber widths of 28.6 \u0026micro;m for kraft pulp and 21.2 \u0026micro;m for sulfite pulp are in accordance with the fibers shown in the SEM images. The average fiber length is approximately 2.1 mm for kraft pulp and about 0.72 mm for sulfite pulp.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eInfluence of the irradiation dose\u003c/h2\u003e \u003cp\u003eThe aim is to investigate how the electron beam dose influences the properties of the pulp, and to examine the differences between kraft pulp and sulfite pulp due to irradiation. The dry kraft pulp (KP) and sulfite pulp (SP) sheets were treated with electron beam doses in the range of 100\u0026ndash;400 kGy at a dose rate of 1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe intrinsic viscosities of kraft pulp and sulfite pulp before irradiation are 484 ml g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 352 ml g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Even with an irradiation dose of 100 kGy, a rapid decrease in the intrinsic viscosity can be observed, reaching values of 73 ml g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (KP) and 71 ml g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (SP) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The irradiation initiates chain scission due to the splitting of glycosidic bonds, leading to the depolymerization of cellulose and as a consequence, in reduction in intrinsic viscosities. An increase of the EBI dose up to 400 kGy results in a further, albeit slight, reduction in the intrinsic viscosities. The rapid decrease in intrinsic viscosity or degree of polymerization (DP) at EBI dosages\u0026thinsp;\u0026lt;\u0026thinsp;100 kGy, followed by a further slight decrease until the so-called level-off DP (LODP) has also been reported in other studies (Driscoll et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Wu et al. \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Lee et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Charlesby \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1955\u003c/span\u003e). While kraft pulp has a higher intrinsic viscosity compared to sulfite pulp before EBI, the EBI treatment leads to very similar values for the both pulp types with 29 ml g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (KP) and 31 ml g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (SP). The very slight differences in intrinsic viscosity between the two pulp types can be explained by the high degradation of cellulose by EBI up to the LODP.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast to the intrinsic viscosity, the fiber length of the kraft pulp remains nearly constant during the EBI treatment up to an EBI dose of 200 kGy, with values of around 2 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Higher EBI doses lead to a reduction in fiber length of up to 0.8 mm at 400 kGy, which corresponds to 40% of the starting material. Sulfite pulp generally has a significantly shorter fiber length of the raw material with 0.7 mm due to the pulping process and the use of hardwood. Irradiation of the pulp leads to a slight, but steady shortening of the fibers, reaching 0.4 mm at 400 kGy (58% of the initial length). In principle, it can be expected that irradiation leads to a shortening of the fibers due to defibrillation, but the extent depends strongly on the type of pulp used. For both pulp types, the fiber width initially decreases slightly (KP) or remains stable (SP), but at a higher irradiation dose, the fibers become somewhat wider (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). This effect of the fiber widening is probably related to the swelling of the fibers due to irradiation and increases with a higher irradiation dose. Choi et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) observed similar effects of fiber swelling with alkali treatment of kraft pulps, increasing the NaOH concentration leads to an increase of the fiber width.\u003c/p\u003e \u003cp\u003eThe WRV of the pulp is investigated by a standard centrifugation technique that measures the amount of water, which remains in the pulp and is related to the swelling behavior. The WRV is influenced by many different factors, such as fiber morphology and composition of the pulp (Mayr et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Botkov\u0026aacute; et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Another influencing factor on the WRV is the amount of hemicellulose due to its contribution to the interfibrillar bonding (Koistinen et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Chen et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) show that a decreasing amount of pentosane leads to a decrease of the WRV.\u003c/p\u003e \u003cp\u003eThe water retention capacity of the kraft pulp is with 87.4% significantly higher than that of sulfite pulp with 64.6%, which might be caused by the higher amount of hemicellulose in the kraft pulp sample as well as the different fiber structure, especially fiber length, of the materials (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). A decrease in the WRV is observed for both pulp samples after EBI treatment, for KP there is a slight increase at an irradiation dose\u0026thinsp;\u0026gt;\u0026thinsp;300 kGy. Previous studies by Fischer et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1987\u003c/span\u003e) also detect a decrease in WRV values with increasing irradiation dose. However, no correlation was found between irradiation dose and WRV, an irradiation dose of 400 kGy leads to values of 66.7% for KP and 50.5% for SP. It is assumed that the reduction of WRV is primarily related to the degradation of hemicellulose during EBI treatment, as the hemicelluloses are able to bind large quantities of water (Koistinen et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Dias et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe zeta potential measurements should provide information about the surface properties of the pulp samples. Different electrokinetic effects can be used to determine the zeta potential. The streaming current or streaming potential method, employed in this study, is most suited for measuring fibers (Jacobasch et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). Since the zeta potential depends not only on the surface potential of the pulp, but also on the properties of the liquid phase, a dependence on the pH-value must be considered. However, fluctuations in the pH range 6\u0026ndash;9 only have a minor effect on the zeta potential values (Anikushin et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Due to the presence of carboxyl and hydroxyl groups by suspension of the pulps in water, a negative charge is measured. The kraft pulp has a zeta potential of -22 mV, which is in accordance with results of other studies on bleached kraft pulp samples (Bhardwaj et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). The irradiation of the kraft pulp does not lead to changes in the zeta potential and values are within in the range of -20 to -28 mV (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). The sulfite pulp has a similar zeta potential of -21 mV before irradiation, but the value increases significantly to -59 mV by an irradiation dose of 400 kGy. It is assumed that the number of functional groups is significantly increased for the sulfite pulp by irradiation. Changes with regard to porosity, pore structure and swelling capacity can also influence the zeta potential and lead to a higher surface charge of the material (Stana-Kleinschek et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Luxbacher \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn addition, the drainage resistance was measured using the Schopper-Riegler (SR) method in accordance to EN ISO 5267-1 (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). The values for the raw material as well as irradiated pulp were in the range of 9 to 13 \u0026deg;SR. These values are within the range assigned to unground pulps, and no dependence of the SR values on the applied electron beam dose can be determined.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eProperties of kraft pulps and sulfite pulps with various irradiation dose.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eKraft pulp (KP)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRadiation dosage [kGy]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIntrinsic viscosity [ml\u0026nbsp;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWater retention [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZeta potential [mV]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eFibre length [mm]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFibre width [\u0026micro;m]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCrI (XRD) [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCrI (NMR) [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e380/1096\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e484\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e87\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.54\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-22\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.07\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e28.6\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e84.0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e48.4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_100_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e62\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-24\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.11\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e27.6\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e84.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_200_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e61\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-28\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.00\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.004\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e27.8\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e84.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_300_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e67\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-20\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.17\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e27.7\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e82.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e67\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-23\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e29.9\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e83.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e45.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSulfite pulp (SP)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e352\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e65\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-21\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.72\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e21.2\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e84.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e47.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_100_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e50\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;1.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-49\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.69\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e21.7\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e84.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e48.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_200_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e48\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-56\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.59\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e22.1\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e84.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e47.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_400_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e51\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-59\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e22.9\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e83.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e45.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe degree of crystallinity is an important factor for the physical, mechanical and chemical properties of the pulps. An increasing degree of crystallinity leads to a decreased swelling and chemical reactivity of the cellulose, while increasing its tensile strength and dimensional stability (Agarwal et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). In order to obtain information on the crystallinity of the pulps used here, Raman, XRD and NMR experiments were carried out. Raman measurements are an important tool for analyzing cellulosic materials because of the weak bands of water and background (Agarwal et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). To determine the crystallinity of cellulose, Schenzel et al. (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) suggest using the peaks at 1481 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1462 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the crystalline and amorphous parts of cellulose, in conjunction with spectral deconvolution. The deconvolution is necessary, since the intensities of the selected bands are relatively low, which can lead to band fitting problems. In contrast, Agarwal et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) propose a univariate analysis based on the peaks at 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1096 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e bands. They detected a strong change in intensity and band shape at the 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1096 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e caused by ball milling, which has a substantial impact on cellulose crystallinity. Schroeder et al. (\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1986\u003c/span\u003e), who found that the fibrous cellulose sample had a much higher intensity than the regenerated cellulose and ball-milled samples, also show the correlation of the band at 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with the cellulose crystallinity.\u003c/p\u003e \u003cp\u003eIn this study, both the bands at 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;5b) as well as at 1462 and 1481 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;5c) were investigated in order to obtain information on the crystallinity of the both pulp samples and the changes resulting from electron beam irradiation. The Raman spectra in the range of 200\u0026ndash;2000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of the kraft pulp and sulfite pulp as well as their samples irradiated with 400 kGy, depicted in Fig.\u0026nbsp;5a, show no significant variations. This leads to the assumption that the cellulose I structure remains mostly unchanged in all samples. For the band at 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, a decrease in intensity with rising irradiation dose can be shown for both the kraft and sulfite samples, which was therefore accompanied by a slight decrease in the 380/1096 ratio. Generally, the sulfite pulp samples exhibit slightly higher intensities at 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicating a higher proportion of crystalline parts compared to the kraft pulp samples. The slight decrease of the values due to irradiation for the 380/1096 ratio can be detected for both pulp types in the same way with a decrease from 0.43 (raw material) to 0.38 (400 kGy) for kraft pulp, and from 0.47 (raw material) to 0.42 (400 kGy) for sulfite pulp.\u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"13\" name=\"Grafik 5\"\u003e\u003c/div\u003eFigure\u0026nbsp;5 Raman spectra for raw materials and irradiated kraft pulps and sulfite pulps with a) full spectra and detailed view of a) the band at 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and b) the bands at 1462 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1481 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIt is noticeable that in all samples, the pulps before and after irradiation, the peak at 1481 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e shifts to a wavenumber of 1479 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. At a wavenumber of 1462 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e no clear peak is recognizable, which also makes a deconvolution of the peaks much more difficult. However, in principle, a slight decrease in crystallinity can also be detected by increasing the irradiation dose, according to the calculation of Schenzel et al. (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite the Raman measurements, X-ray diffraction of the (irradiated) pulp samples was carried out in order to get information about their crystalline structure. The diffraction patterns of kraft and cellulose pulp irradiated with 400 kGy show no difference or peak shifts compared to the raw materials, indicating that the structure of the pulps remain unchanged (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). All patterns exhibit the characteristic diffraction peaks of the cellulose I\u0026szlig; structure at 2θ\u0026thinsp;=\u0026thinsp;15\u0026deg;, 16.5\u0026deg;, 22.5\u0026deg; and 34.5\u0026deg;, which correspond to the (1\u0026ndash;10), (110), (200) and (004) crystallographic planes, respectively (Lee, et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Wu, et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; French, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The crystallinity index (CrI, XRD) was calculated using the Segal method (Segal et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1959\u003c/span\u003e) in order to compare the influence of the EBI treatment on the crystalline structure. Furthermore, the crystalline (86.6\u0026ndash;92 ppm) and amorphous (79.8\u0026ndash;86.6 ppm) parts were used to determine the crystallinity (CrI, NMR) by NMR experiments (Liiti\u0026auml; et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Tee\u0026auml;\u0026auml;r et al. \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Schenzel et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The CrI from XRD diffraction reaches values of 83\u0026ndash;85%, and the CrI from NMR experiments shows values in the range of 45\u0026ndash;49%, which are in good accordance with studies from Liiti\u0026auml; et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). The CrI values show similar trends for both methods, initially rising slightly at an irradiation dose of 100 kGy and then decreasing very slightly up to an irradiation dose of 400 kGy. However, the change in crystallinity and dependence on the irradiation dose up to 400 kGy is extremely small for both kraft pulp and sulfite pulp samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Lee et al. (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) also report CrI values in the same range (83\u0026ndash;85%) at EBI doses up to 500 kGy, only EBI doses above 2000 kGy lead to a decrease below 80%. Other studies also show that there is no significant relationship between irradiation and crystallinity (Schnabel et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Morin et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Hwang et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). It is suggested that, in contrast to acid hydrolysis, the chain scission caused by EBI is more random. The EBI attacks both the amorphous and crystalline regions of cellulose because radicals are generated in both. In contrast, acid hydrolysis mainly leads to chain scission in the amorphous region (Hwang et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Because of the attack on both the crystalline as well as the amorphous regions, it is assumed that the CrI does not change with the EBI doses used in this study. Using different methods, Raman (380/1096 ratio), XRD (Segal method), and NMR, very similar trends were observed, namely that the crystallinity of the pulp samples is nearly unaffected by electron beam irradiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition, IR measurements were carried out, mainly to investigate the occurrence of carbonyl groups in the pulp samples due to irradiation, because this was shown in some previous studies (Henniges et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Sarosi et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Hwang et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e depicts that there are no obvious changes in the IR spectra of kraft pulp and sulfite pulp irradiated at 400 kGy compared to the raw material, or between the two pulp types itself. Other cellulosic materials also show no change in their IR spectra due to EBI treatment (Kim et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Wu et al. \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). A prominent band for carbonyl vibrations can be found in the IR spectra of cellulose at wavenumbers near 1720 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. We observed an increasing yellowing of the pulps with higher irradiation dose, suggesting that EBI causes carbonyl group formation. However, the band near 1720 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cannot be detected in the samples prepared in this study. This indicates that there is no formation of carbonyl bands due to EBI. It is assumed that the occurrence of carbonyl groups, as indicated by EBI, requires a significantly higher irradiation dose, or the amount is so low that it cannot be detected by IR measurements. Lee et al. (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) also show just a very small IR peak for cellulose pulp treated with 1000 kGy. The yellowing of the pulps can also result from the formation of furfural due to the degradation of hemicelluloses, which turns yellow by exposition to light and air. Furfural is usually obtained by an acid-catalyzed dehydration of xylan (Binder et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The bands at 1052 and 1104 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e arise from C-O-C asymmetric stretching and C-O/C-C stretching at cellulose linkage, and the slight decrease in the intensity of these bands for the irradiated samples indicates glycosidic cleavage through irradiation.\u003c/p\u003e \u003cp\u003eThe SEM images in Fig.\u0026nbsp;7 show the morphology of the sulfite pulp samples irradiated at 100, 200 and 400 kGy in comparison to the starting material as well the kraft pulp sample irradiated at 400 kGy. In general, the fiber structure of the pulp remains intact, but an increasing irradiation dose leads to a progressive defibrillation of the fibers and the fibers also appear increasingly flatter and wider. This is consistent with the measured increase in fiber width. Similar observations can be made for the kraft pulp sample irradiated at 400 kGy with a defibrillation of the fibers, as well as significantly wider fibers compared to the starting material. This is in accordance with other studies, where the physical structure also remains fiber-like and no significantly changes can be observed (Lee et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Wu et al. \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"2\" name=\"Grafik 2\"\u003e\u003c/div\u003eFigure\u0026nbsp;7 SEM images of irradiated sulfite pulp and kraft pulp samples at various irradiation dose (1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, dry sheets) at a magnification of 1,000x.\u003c/p\u003e \u003cp\u003eThe hemicellulose content and composition of both pulp samples as well as the changes resulting from EBI treatment were analyzed by HPLC measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). Kraft pulp contains a significantly higher amount of hemicellulose with 13.7% compared to sulfite pulp with 2.1%. The main components in kraft pulp are xylose and mannose. Using an EBI dose of 400 kGy leads to the decomposition of the hemicelluloses to a total amount of 10.6%, while the glucose amount decreases from 82.1% to 72.9%. In contrast, the hemicellulose content decreases very slightly due to irradiation with 200 kGy for the sulfite pulp (1.9%), whereas significant decomposition of glucose can be observed. However, the HPLC measurements show that, even after irradiation, kraft pulps have a high amount of hemicellulose and a composition that differs significantly from those of the sulfite pulps, which influences the properties of the materials as well as their further use as material in the preparation of microfibrillated cellulose.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eVariation in the irradiation process (atmosphere and dose rate)\u003c/h2\u003e \u003cp\u003eBesides the irradiation dose, there are many other influencing factors in the EBI process, such as the dose rate, temperature, and humidity, but also the surrounding medium. Additional investigations were therefore carried out at an irradiation dose of 400 kGy to determine the extent, to which the irradiation of dry and wet samples in air or a nitrogen atmosphere influences the both pulp samples. The dose rate was also varied to 0.67 and 1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt was expected that the irradiation of wet samples or in a nitrogen atmosphere leads to an attack in other regions of the cellulose and an altered radical formation compared to the irradiation of dry samples in air. For the intrinsic viscosity, the values of the irradiated samples under different conditions are in the same range, just the wet sulfite pulp shows a slightly greater decrease compared to the other samples. Therefore, the main influencing factor for the degradation of the pulps is the irradiation dose, which is also shown by Hwang et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) for dry and wet cellulose papers in the range of 25 to 100 kGy. In contrast, Henniges et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) observed at the irradiation dose of 40 and 60 kGy a higher degradation of wet pulps than of untreated dry pulps and lower values for the molar mass.\u003c/p\u003e \u003cp\u003eThe wet conditions in the irradiation process lead to a higher swelling of the fibers for both pulp samples and, therefore, to an increase of the fiber width compared to the dry or under nitrogen irradiated pulps. This change in the swelling behavior results in a higher WRV for the wet irradiated samples, except for KP_400_50_W. No dependence of the dose rate on the fiber dimensions or the WRV could be determined. The values for the zeta potential are also slightly lower for the wet irradiated samples compared to the dry ones, which is related to a change in the swelling behavior or a decrease in functional groups on the surface. This contradicts the theory that more radicals are produced by wet conditions, leading to a rapid oxidation and a higher carbonyl and carboxyl content in the pulp samples (Henniges et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eProperties of kraft pulps and sulfite pulps irradiated with 400 kGy under different conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eKP_400_50_D\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIntrinsic viscosity [ml\u0026nbsp;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWater retention [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eZeta potential [mV]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFibre length [mm]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eFibre width [\u0026micro;m]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCrI [%] (XRD)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCrI [%] (NMR)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e380/1096\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"1\" nameend=\"c10\" namest=\"c10\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.46\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-23\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.85\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.9\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e83.5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e45.3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_50_W\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-18\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.92\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.012\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e33.2\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e77.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_50_N2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e69\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-21\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.2\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e82.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_5_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e61\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-25\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.08\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.6\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e83.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_5_W\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e74\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-20\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.67\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e32.2\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e83.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_400_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e51\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-59\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.9\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e83.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e45.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_400_50_W\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-53\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e24.6\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e84.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e46.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_400_50_N2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e48\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-41\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.44\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.1\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e83.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e45.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_400_5_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e48\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-61\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.9\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e81.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSP_400_5_W\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e59\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;2.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-50\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e24.8\u003c/p\u003e \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e83.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe Raman spectra of dry and wet irradiated samples show no difference neither for kraft pulp nor for sulfite pulp, pointing that the different states (dry or wet) during irradiation in air have no influence on the structure of the material (Fig.\u0026nbsp;8a). The peaks at a wavenumber of 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e also have a very similar intensity, indicating that there is no decrease in crystallinity (Fig.\u0026nbsp;8d, e). Some changes can be detected for the samples irradiated under a nitrogen atmosphere. The intensity of the 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e peak is slightly higher for the irradiated pulps under nitrogen compared to the samples irradiated in air. It is assumed that the amorphous regions of cellulose are more likely to be attacked under a nitrogen atmosphere, resulting in a slightly higher 380/1096 ratio. Furthermore, a slightly lower intensity can be determined for the bands at 1337 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e caused by HCC, HCO, and COH bending, as well as at 1035 and 1057 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is due to CC and CO stretching vibrations (Fig.\u0026nbsp;8b, c) (Schenzel and Fischer \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Wiley and Atalla \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e1987\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"15\" name=\"Grafik 7\"\u003e\u003c/div\u003eFigure\u0026nbsp;8 Raman spectra for kraft pulps and sulfite pulps irradiated with 400 kGy and a dose rate of 1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e under different conditions with a) full spectra and detailed view of b) the band at 1096 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and c) the bands between 1300\u0026ndash;1400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, as well as the detailed view for the band at 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for d) kraft pulp and e) sulfite pulp samples.\u003c/p\u003e \u003cp\u003eNo changes in the IR spectra due to the different atmospheres or dose rate were detected for both pulp types (Fig. S2a) and, as for the irradiation dose, no occurrence of carbonyl groups at a wavenumber around 1720 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e can be observed. The XRD diffractograms (Fig. S2b) are also very similar, with CrI (XRD) values ranging from 82 to 84%, the CrI values from NMR experiments are in the range of 45\u0026ndash;47%. Only the kraft pulp sample KP_400_50_W irradiated as a wet sheet shows a higher reduction in crystallinity and has a CrI value of 77.4%. It is assumed that the radicals lead to a higher chain scission in the crystalline regions of cellulose, which leads to a decreasing crystallinity combined with a higher swelling capacity and thus wider fibres.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;9 depicts the SEM images of the kraft pulps and sulfite pulps that were irradiated with 400 kGy under different atmospheres. The defibrillation of the wet irradiated samples appears to be somewhat lower, and the surface of the fibers is slightly smoother, compared to the dry irradiated samples in air. Furthermore, irradiation of the wet samples leads to a higher fiber width because the swelling is promoted. In contrast, the nitrogen atmosphere favors the preservation of the fiber structure, especially in case of sulfite pulp, where the fibers appear less flat than the samples irradiated in air. The defibrillation of the fibers is very similar for the irradiation under air (dry) and nitrogen atmospheres.\u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"3\" name=\"Grafik 3\"\u003e\u003c/div\u003eFigure\u0026nbsp;9 SEM images of sulfite pulp and kraft pulp samples irradiated under different conditions (dose: 400 kGy, dose rate: 1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) at a magnification of 1,000x.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of microfibrillated cellulose\u003c/h2\u003e \u003cp\u003eMicrofibrillated cellulose can be prepared from the irradiated pulps in a relatively simple way using high-pressure homogenization. Before the high-pressure homogenization, the pulps are only stirred and dispersed, but no further chemicals are required. However, it is therefore not possible to prepare MFC with all irradiated pulp samples, as insufficient pre-treatment leads to increased blockages in the high-pressure homogenizer. This is particularly the case with kraft pulp irradiated at \u0026le;\u0026thinsp;200 kGy. These tests were discontinued and no further characterization was carried out. It is assumed that sulfite pulp is easier to defibrillate, even at lower irradiation dose, because its fibers already have no primary walls, unlike kraft pulp. A limiting factor in determining whether MFC can be produced from the irradiated pulp in a high-pressure homogenizer without blockages appears to be the fiber length. Since sulfite pulp already has a shorter fiber length, the production is somewhat easier compared to kraft pulp, even at lower irradiation dose.\u003c/p\u003e \u003cp\u003eThe particle size of the MFC was measured using laser diffraction. Although this method is only partially suitable for measuring fibers, it is a fast and easy way to demonstrate the changes in the MFC, and the values are in a very good accordance with the fiber widths measured with the Fiber tester (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). The particle size of the MFC prepared from dry irradiated sulfite pulp decreased from 24.9 \u0026micro;m to 14.9 \u0026micro;m as the irradiation dose increased from 100 to 200 kGy (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;10a). However, increasing the irradiation dose further to 400 kGy leads to an increase in particle size to 28.7 \u0026micro;m, which is presumably related to the formation of numerous agglomerates. The same tendency is also observed for MFCs prepared from the irradiated kraft pulp, which exhibit an increase in particle size from 13.2 \u0026micro;m to 20.9 \u0026micro;m at irradiation dose of 300 and 400 kGy. MFCs prepared from the wet irradiated samples have significantly smaller particle sizes compared to the dry irradiated samples under air. Probably, the structure and properties of the pulps are changed by irradiation under wet conditions in such a way that the fibers are significantly more comminute by dispersing and high-pressure homogenization, and at the same time less prone to agglomerate formation. For the samples under a nitrogen atmosphere, the resulting MFC for kraft pulp is relatively similar to the dry irradiated sample, whereas for sulfite pulp a significantly smaller particle size is detected. Furthermore, the particle size distribution is narrower for all MFCs prepared from kraft pulp, independent of the irradiation conditions, than for the MFCs prepared from sulfite pulp. Raman measurements of the MFCs from sulfite pulp (SP_x_50_D) show a decrease of the intensity of the 380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band when the irradiation dose increases from 200 to 400 kGy, indicating a decrease in crystallinity (Fig. S3).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean particle size (D50) of MFC prepared from irradiated kraft pulp and sulfite pulp samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eKP_100_50_D\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD50 [\u0026micro;m]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eD50 [\u0026micro;m]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_100_50_D\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24.9\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_200_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_200_50_D\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_400_50_D\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e28.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_50_W\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_400_50_W\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_50_N2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_400_50_N2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_5_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_400_5_D\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e55.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_5_W\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_400_5_W\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"10\" name=\"Grafik 10\"\u003e\u003c/div\u003eFigure\u0026nbsp;10a) Mean particle size of MFC prepared from SP and KP samples irradiated under different conditions in dependence on the irradiation dose, as well as corresponding particle size distributions of MFC from sulfite pulp samples with different b) irradiation dose and d) irradiation conditions and c) particle size distribution of MFC from kraft pulp samples irradiated at 400 kGy under different conditions.\u003c/p\u003e \u003cp\u003eThe SEM images in Fig.\u0026nbsp;11 show the MFC prepared from irradiated sulfite pulp with different irradiation doses. The MFC from the 100 kGy irradiated pulp sample appears more as a net-like mesh, whereby the fibers are still clearly visible and some individual wider fibers are also present. At an irradiation dose of 400 kGy, MFC is produced, in which individual fibers are no longer clearly visible and only shorter particles are present. The aggregation of these particles can be observed in the SEM images, which is consistent with the previously measured higher values of the mean particle size for this sample. If the MFCs are air-dried, an increasing yellowing and a lock of film formation can be observed with higher irradiation dose of the sulfite pulp (Fig. S5).\u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"4\" name=\"Grafik 4\"\u003e\u003c/div\u003eFigure\u0026nbsp;11 SEM images of MFC prepared from irradiated sulfite pulp samples with different irradiation doses at magnifications of 10,000x and 30,000x.\u003c/p\u003e \u003cp\u003eThe MFCs produced from kraft pulps and sulfite pulps irradiated at 400 kGy under different conditions (dry, wet, nitrogen atmosphere) exhibit very different morphologies (Fig.\u0026nbsp;12). Especially the wet irradiated pulps result in MFCs with a significantly more homogeneous surface structure and smaller particles than those produced from the dry irradiated pulps. The MFCs prepared from the irradiated pulps under nitrogen atmosphere also have smaller particles than the dry irradiated samples under air, but the particles are more aggregated than wet irradiated samples. Furthermore, a higher defibrillation can be observed for the MFCs from sulfite pulp compared to kraft pulp. While the morphology of MFCs prepared from kraft pulp is very similar for dry irradiated samples with a change of the dose rate from 1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 0.67 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, significant differences can be observed for wet-irradiated kraft pulp samples. The MFCs from KP_400_5_W have very short particles and no fiber structure can be detected in comparison to KP_400_50_W (Fig. S4).\u003c/p\u003e \u003cp\u003e \u003cdiv description=\"\" class=\"Drawing\" id=\"5\" name=\"Grafik 5\"\u003e\u003c/div\u003eFigure\u0026nbsp;12 SEM images of MFC prepared from KP and SP samples irradiated with 400 kGy and a dose rate of 1.41 kGy s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e under different conditions at magnifications of 1,000x and 30,000x.\u003c/p\u003e \u003cp\u003eAs expected, the molar mass of kraft pulp is higher than that of sulfite pulp, with values for M\u003csub\u003eN\u003c/sub\u003e of 368,210 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (KP) and 178,870 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (SP). These difference between the two pulp types is in accordance with previous studies (Duan et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Irradiation leads to a significant decrease in molar mass due to degradation of the pulp. The M\u003csub\u003eN\u003c/sub\u003e for irradiated kraft pulp is lower than that of sulfite pulp, which could be related to the higher irradiation dose for KP. The further dispersion and high-pressure homogenization in order to prepare MFC leads only to a slight decrease of the molar mass and a narrower distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e13\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDynamic light scattering confirms the results of the particle size measurement with regard to the significant increase in mean particle size for MFC prepared from sulfite pulp when the irradiation dose was increased from 200 to 400 kGy (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Fig. S6). As the methods used to determine the particle size differ significantly between laser diffraction and dynamic light scattering, the values can only be compared within each method. Nevertheless, the same trend can be seen in both methods, namely that the particle size of MFC initially decreases with an increasing irradiation dose applied to sulfite pulp, and then increases again, presumably due to the formation of agglomerates.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean particle size (D50) of MFC from kraft pulp and sulfite pulp samples with different irradiation dose measured by dynamic light scattering\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eKP_100_50_D\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD50 [nm]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eD50 [nm]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_100_50_D\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1575.8\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_200_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_200_50_D\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e876.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKP_400_50_D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e826.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eSP_400_50_D\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3873.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, it is demonstrated that electron beam irradiation is a suitable pre-treatment method for pulps in the production of microfibrillated cellulose. As expected, the irradiation dose significantly influences the properties of the pulp, especially the intrinsic viscosity has a strong decrease even at a dose of 100 kGy, which continues at higher doses up to 400 kGy, albeit more slightly. In contrast, no significant change in crystallinity can be detected using Raman, XRD, or NMR measurements. This is because radicals are generated throughout the cellulose by electron irradiation and presumably react in both the crystalline and amorphous areas. The two pulp types differ in fiber length; while the fiber length of the long pulp from the kraft process decreases from irradiation dose of 300 kGy, the fiber length of short pulp from the sulfite process decreases only slightly overall. A change in the atmospheric conditions results in minor changes, such as increased swelling in wet irradiated pulps. It appears that the fiber length is the decisive factor in determining whether direct high-pressure homogenization of the pulp is possible without further pre-treatment to obtain MFC. If the irradiation dose is too high, this results in the formation of agglomerates during the production of MFC, characterized by a larger particle size. Electron beam irradiation proves to be a sustainable effective pre-treatment method, especially since the addition of other chemicals can be avoided entirely. However, finding a suitable irradiation dose for each pulp type remains challenging.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments: \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank Prof. Dr. Thomas Heinze (Institute for Organic Chemistry and Macromolecular Chemistry, Center of Excellence for Polysaccharide Research, Friedrich Schiller University, Jena) for the SEC measurements, Dr. Jens Schaller (Thuringian Institute for Textile and Plastic Research, Rudolstadt, Germany) for the dynamic light scattering measurements and Dr. Erica Brendler (TU Bergakademie Freiberg, Institute of Analytical Chemistry, Germany) for the 13C NMR measurements. Furthermore, big thanks go to the Institute of Natural Materials Technology, working group paper technology (TU Dresden, Germany) for the possibility to use the wet lab for WRV and Zeta potential measurements as well as to Annett Völlmar for measuring the fiber dimensions of the pulps.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was funded by the German Research Foundation (DFG) in the project Cellstor, grant number 511521214 (FI755/16-1, MI945/8-1).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJohanna Fischer: Conceptualization, Preparation of MFCs, Methodology, Investigation, Writing – Original draft\u003c/p\u003e\n\u003cp\u003eMichael Thomas Müller: Electron beam irradiation of pulps, Writing – Review and Editing\u003c/p\u003e\n\u003cp\u003eKatrin Thümmler: Conceptualization, Writing – Review and Editing\u003c/p\u003e\n\u003cp\u003eBjörn Günther: Methodology – SEM, Writing – Review and Editing\u003c/p\u003e\n\u003cp\u003eDaria Mikhailova: Methodology – XRD, Funding, Writing – Review and Editing\u003c/p\u003e\n\u003cp\u003eSteffen Fischer: Conceptualization, Funding, Supervision, Writing – Review and Editing\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAgarwal UP, Reiner RS, Ralph SA (2010) Cellulose I crystallinity determination using FT-Raman spectroscopy: univariate and multivariate methods. 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Ind Crops Prod 209:118035. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.indcrop.2024.118035\u003c/span\u003e\u003cspan address=\"10.1016/j.indcrop.2024.118035\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"pulp irradiation, microfibrillated cellulose, electron beam irradiation, high-pressure homogenization","lastPublishedDoi":"10.21203/rs.3.rs-9028732/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9028732/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAn innovative approach for the production of microfibrillated cellulose (MFC) using a combination of high-pressure homogenization and electron beam irradiation (EBI) pre-treatment is proposed. In contrast to conventional pre-treatments for the production of MFC, electron beam treatment is a completely chemical-free method. This study focuses particularly on the extent to which the conditions of the electron beam irradiation, in terms of dose, dose rate, and atmosphere, influence the properties of the pulps and the resulting MFC. The effects on the both pulp types kraft pulp (KP) and sulfite pulp (SP) were compared. An irradiation dose of 100 kGy already leads to a significant decrease in the intrinsic viscosity of both types of pulp, while the crystallinity of the samples remains largely unaffected. It was demonstrated that EBI with a suitable irradiation dose, which varies greatly in dependence on the pulp type, is a promising approach for fast, effective, and chemical-free pre-treatment.\u003c/p\u003e","manuscriptTitle":"Microfibrillated cellulose prepared by electron beam irradiated pre-treatment – a comparison of various influencing factors with regard to material and process","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-30 04:53:24","doi":"10.21203/rs.3.rs-9028732/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0f29022f-5175-497c-97ac-464727aef6bb","owner":[],"postedDate":"March 30th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-30T04:53:25+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-30 04:53:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9028732","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9028732","identity":"rs-9028732","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}