Sulfated cellulose pulp with ultra-high water retention characteristics

Sulfated cellulose pulp with ultra-high water retention characteristics | 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 Sulfated cellulose pulp with ultra-high water retention characteristics Sakura Morimitsu, Ayato Nishimura, Kenzo Deguchi, Yuuki Mogami, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5147146/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Jul, 2025 Read the published version in Cellulose → Version 1 posted 11 You are reading this latest preprint version Abstract A sulfated cellulose pulp (SCP) exhibiting ultra-high water retention properties, has been developed and its water retention mechanisms have been analyzed based on its molecular structure determined by solid-state 13 C nuclear magnetic resonance (NMR). Cellulose pulp (CP) wood-derived was sulfated using sulfamic acid and urea reaction system with varying concentrations of sulfamic acid. SCP has 1.31–1.91 mmol/g of sulfate groups and exhibits a high water retention value (WRV) of 16000%, which is approximately 100 times greater than that of CP. After the sulfate reaction, a new peak at 69 ppm was observed in the solid-state 13 C NMR spectrum, which was assigned to the sulfated C6. Quantitative analysis indicated that approximately 18% of C6 in CP was converted to sulfated C6. WRV increased almost linearly with the amount of sulfated C6, which played an important role in the water retention capacity. SCP was proven very promising as a novel functional material, owing to the molecular mechanisms involved. Cellulose Sulfated cellulose pulp Water retention Solid-state 13C NMR Sulfate group Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Sulfated cellulose pulp (SCP) has attracted considerable attention in recent years for its ability to produce cellulose nanofibers, which is a fiber isolated to the smallest unit that constitutes a cellulose fiber. Several synthetic methods for SCPs have been proposed, such as sulfuric acid hydrolysis (Rånby et al. 1949 ), the HSO 3 Cl/(CH 3 CO) 2 O system (Zhang et al. 2011 a), the sulfamic acid/urea/ N , N -dimethylformamide system (Huang and Zhang 2010 ), the HSO 3 Cl/ N , N -dimethylformamide system (Zhao MW et al. 2007 ), and the deep eutectic solvent system (DES, CP/sulfamic acid/urea system without water) (Sirviö et al. 2019 ). Similar to those modified by carboxyl (Saito et al. 2007 ) and phosphate groups (Ghanadpour et al. 2015 ; Noguchi et al. 2017 ), sulfated cellulose pulp is also defibrillated by mechanical treatment in a high-pressure homogenizer, resulting in nanofibers. Nanofibers have been applied to functional materials such as O 2 gas barrier films (Fukuzumi et al. 2009 ), rheology control agents (Wang et al. 2019 ), and metal ion adsorbents (Liu et al. 2015 ; Liu et al. 2016 ). Recently, our group has presented the synthesis of SCP using a CP/sulfamic acid/urea system, affording a water retention value (WRV) of approximately 3000% (Nishimura and Otsuka 2023a), and enhanced water dispersion stability and transparency in aqueous dispersion (submitted). The mechanism by which SCP appears transparent in water has been discussed in terms of its fiber morphology and is attributed to the swollen fiber structure of the SCP fibers. However, its molecular structure has not been clarified yet. Structural analyses are crucial for understanding the functions of SCPs. Solid-state 13 C nuclear magnetic resonance (NMR) is one of the best analytical approaches, providing structural information at the molecular level even for insoluble samples. The sulfate group of SCP was previously investigated using the 1 H- 13 C cross-polarization/magic angle spinning (CPMAS) method (Zhang et al. 2011 b), indicating that the hydroxyl group at the C6 position of the cellulose pulp is involved in the sulfation reaction. CPMAS can provide useful structural information. However, it should be noted that this technique is not quantitative. Although the measurement time takes longer than CPMAS, direct polarization/magic angle spinning (DDMAS) is highly reliable in quantifiability because 13 C can be measured directly without passing through 1 H magnetization. To the best of our knowledge, no studies have reported 13 C DDMAS experiments on SCP. In this study, a novel SCP was synthesized using the CP/sulfamate/urea reaction system, exhibiting ultra-high water retention capacity. Furthermore, its water retention mechanisms are discussed based on the structural information obtained by 13 C DDMAS. Materials and methods Materials The cellulose pulp (CP) used in this study was never-dried softwood-bleached kraft pulp (Marusumi Paper Co., Ltd., Japan). The concentration of the CP slurry was adjusted to 25 wt%, and the water used for the CP slurry was replaced from industrial to pure water. Sulfamic acid (H 2 NSO 3 H), urea ((H 2 N) 2 C=O), sodium hydroxide (NaHCO 3 ), and sodium hydrogen carbonate (NaOH) were purchased from FUJIFILM Wako Pure Chemical Co. All the materials were used without further purification. The ion-exchange resin was purchased from Organo Co., Japan. Pure water (distilled by Marusumi Paper Co., Ltd., Japan, conductivity < 0.1 mS/m, pH 5–8) was used in all the experiments. Sulfation of cellulose pulp The sulfate reaction solution was prepared by adding and stirring S (1.25–5.00 g, 0.013–0.051 mol) and U (2.50 g, 0.042 mol) with pure water (12 g) at room temperature (296 K). The 25 wt% CP (8 g, BD2 g) was immersed in the sulfate reaction solution for 10 min, spread thinly and uniformly on an acrylic plate, and dried at 358 K for 3 h using a constant-temperature dryer (DKN602, Yamato Scientific Co. Japan). The dried CP reacted when heated to 413 K for 30 min. The reactants were neutralized with NaHCO3 and washed with pure water on a 330-mesh sieve (Sampo Co., Japan). The sulfated cellulose pulp slurry was adjusted to a concentration of 1.0 wt% with pure water and then refrigerated at 277 K. The reaction conditions were determined at 5 different molar ratios (R), where R was determined by dividing the number of moles of S by the number of moles of the anhydroglucose units in CP. The moles of anhydroglucose units were calculated from the dry weight of the pulp/162. Water retention value The water retention value (WRV) was measured using the TAPPI method and 10 g of the 0.5 wt% SCP slurry. The SCP slurry was centrifuged at 3000 g for 15 min and the WRV was calculated using the following Eq. ( 1 ). $$\:\text{W}\text{R}\text{V}\left(\text{%}\right)=\frac{Ww-Wd}{Wd}\times\:100\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:$$ 1 where Ww is the mass after centrifugation and Wd is the mass after drying the sample at 358 K for 24 h. Solid-state C NMR Freeze-dried SCP was powdered using a blender (WB-1; Osaka Chemical Co., Osaka, Japan). 1 H and 13 C NMR experiments were performed at 500.194 and 125.774 MHz, respectively, on an 11.7 T JEOL ECZ 500 spectrometer (JEOL, Tokyo, Japan) using a 4 mm magic-angle spinning (MAS) probe at room temperature. Potassium bromide was used to adjust the magic angle, and adamantane was used as the reference. Standard ramped cross-polarization (CP), direct-polarization (DD), and Torchia sequences (Torchia 1978 ) were used with a MAS frequency of 15 kHz and high-power irradiation to achieve heteronuclear decoupling during each detection period. For 13 C CPMAS, the following parameters were used: π/2 for 1 H, 3.3 µs; mixing time, 5 ms; spectral width (SW), 400 ppm; data points (DP), 1024; recycle delay time (RD), 5 s; accumulations, 1000–1200 scans. For 13 C DDMAS, the following parameters were used: π/2 for 13 C, 3.3 µs; RD, 1200 s; accumulations, 260–300 scans; the other parameters were the same as those of 13 C CPMAS. For Torchia experiments of T 1 measurements, the following parameters were used: RD, 4 s; accumulations, 700 scans; interval time, 1, 1.39, 1.95, 2.71, 3.79, 5.25, 7.37, 10.28, 14.34, 20.0, 50.0, 80.0, 125.0, and 200 s; the other parameters were the same as those of the 13 C CP/DDMAS experiments. All NMR spectra were processed and analyzed using DELTA software (JEOL USA, Inc.). Conductometric titration of contents The amount of sulfated groups of SCP was determined by conductometric titration (Nishimura and Otsuka 2023b). The 1.0 wt% SCP slurry was adjusted to a 0.2 wt% SCP slurry. The 0.2 wt% SCP slurry was added to an ion exchange resin (1.0 g) and stirred for 1 h. After stirring, the ion-exchange resin was removed from the 0.2 wt% SCP slurry using a filter. The 0.2 wt% SCP slurry was titrated by adding a small amount of 0.1M NaOH using a pipette. The amount of sulfate groups was estimated from the moles of 0.1 M NaOH required for neutralization. Fourier-transform infrared spectroscopy The Fourier-transform infrared (FTIR) spectra of CP and SCP were recorded on a Fourier transform infrared spectrometer (Shimadzu Corp., Japan) at the transmission mode, with a resolution of 4 cm − 1 . Results and discussion Figure 1 shows the WRV results of SCP for different R values. WRV increased slightly as the R value increased from 0 to 1.05, and increased almost linearly as the R value increased above 1.05. The maximum WRV reached approximately 16000% when the R value was 4.19, which is approximately 100 times greater than that of CP. Apart from a recent study reporting a WRV of 3000%, previous studies have shown that the WRV of TEMPO-oxidized CP is approximately 400% at about 1.5 mmol/g of carboxyl groups (Saito et al. 2007 ), while phosphorylated CP has a WRV of approximately 900% at about 1.9 mmol/g of phosphorus groups (Hou et al. 2022 ). The molecular structure of SCP was investigated by solid-state 13 C NMR spectroscopy to elucidate the reason for the significant increase in WRV. Figure 2 (a) shows the 13 C CPMAS NMR spectrum of CP with the spectral assignment based on the literature (Atalla and VanderHart 1999 ; Foston 2014 ; Solum 1996 ). C6 cry and C6 am denote the crystalline and non-crystalline C6 signals, respectively. The C6 am peak was observed at 62 ppm, the C6 cry peak was at 65 ppm, the C2, 3, 5 carbon peaks were located between 70 and 78 ppm, the C4 am peak was at 84 ppm, the C4 cry carbon peak was at 89 ppm, and the C1 peak was at 105 ppm. Figure 2 (b) shows the 13 C CPMAS NMR spectrum of SCP at R = 4.19. A new peak was observed in the spectrum of SCP at 69 ppm, which was attributed to the sulfated C6 carbon (Zhang et al. 2011 b). The intensities of the peaks increased as those of C6 am decreased, confirming that C6 am was involved in the reaction. DDMAS method is valid for quantitative measurements of the above structural changes if RD is set to more than five times that of T 1 . The longest T 1 in CP, which is believed to be the same as that in SCP, was 163 s for C4 cry . Under these experimental conditions, RD was set at 1200 s so that the intensity of each signal was guaranteed to be quantitative. Figure. 3 shows the solid-state 13 C DDMAS NMR spectra of the SCP with R values ranging from 0 to 4.19. The peak intensity derived from the sulfate groups of SCP at 69 ppm increased as the R value increased from 0 to 4.19. Furthermore, the C6 am peak at 62 ppm decreased as R increased from 1.05 to 4.19, whereas the C6 cry peak at 65 ppm did not exhibit any significant change. CP consists of alternating crystalline and non-crystalline regions (Wickholm et al. 2009). The crystalline region of CP was hardly accessible in the sulfated reaction because of its regularly lined and high-density composition. Moreover, the non-crystalline sections of CP are irregular and flexible, which enhances the reactivity of the chemicals (Yu and Wu 2010 ). Therefore, the C6 am at 62 ppm was preferentially sulfated, while the other peaks remained virtually unchanged after the reaction. Quantitative measurements of SCP focused on the peaks between 57 and 70 ppm regarding C6. Figure 4 shows the deconvolution of sulfated C6 in the 13 C DDMAS NMR spectra of SCP with (a) R = 1.05 and (b) R = 4.19. Deconvolution of the signals was performed using Voigt functions. The percentage of C6 converted to sulfated C6 in CP was calculated by comparing the intensities of each peak. Figure 5 shows the correlation between the amount of sulfated groups at C6 in SCP and the R values. The amount of sulfate groups increased as the R value increased from 1.05 to 2.09 and continued to increase slightly as the R value increased from 2.09 to 4.19. Sulfated C6 was almost absent when R = 1.05. The maximum value of sulfated C6 was approximately 18% when R = 4.19. These experimental results indicate that the amount of sulfated C6 plays a significant role in WRV. In the cellulose molecules, some hydroxyl groups extend outward onto the surface of the microfibrils. In the case of CP, some microfibrils are closely packed together via hydrogen bonds between the exposed hydroxyl groups. However, when the hydroxyl groups are replaced with polar sulfate groups, the sulfate reaction results in electron repulsion and steric hindrance. This increases WRV because space is created for water to enter. Figure 6 shows the correlation between the entire content of the SCP sulfate groups determined by the electrical conductivity method and the R values. The total amount of sulfate groups increased from 0 to 1.33 mmol/g as the R value increased from 0 to 1.05, and continues to increased slightly from 1.35 to 1.91 mmol/g as the R value increased from 2.09 to 4.19. The maximum total amount of sulfate groups reaches 1.91 mmol/g when R = 4.19, which is nearly equivalent to that of the amount of modifiable hydroxyl groups of C6 present on the surface of microfibrils (Isogai 2018 ). Additionally, although the sulfated C6 was almost absent when R was 1.05 (Fig. 6 ), the sulfate groups content was 1.33 mmol/g. Such results indicate that sulfate groups are mainly introduced to the hydroxyl groups at the C2 and C3 positions of CP in the sulfation reaction when the concentration of sulfamic acid is low. When the concentration is high, sulfate groups are introduced into the hydroxyl groups at C6. The steric hindrance of the C6 primary hydroxyls is greater than that of the secondary hydroxyls of C2 and C3. Therefore, SCP has more spaces where water can enter, causing a significant increase in WRV when R is above 1.05. Fourier-transform infrared spectroscopy was used to verify the sulfation of the hydroxyl groups in CP. Figure 7 shows the infrared spectra of (a) CP and SCP with R values of (b) 0, (c) 1.05, (d) 2.09, (e) 3.14, and (f) 4.19. The intensity of the peaks at 810 and 1230 cm − 1 gradually increased as the R value increased. The peak at 810 cm − 1 was attributed to S = O vibrations and that at 1230 cm − 1 was attributed to C-O-S vibrations. However, S = O and C-O-S vibrations were almost nonexistent in the spectra of CP and SCP with R = 0. Therefore, urea is not directly involved in the sulfate reaction of CP, supporting the preferential sulfation of hydrogen groups. Conclusions A novel SCP was developed using a sulfate reaction with CP, exhibiting a WRV of 16000% for R = 4, which was 100 times greater than that of CP. Solid-state 13 C NMR was used to investigate and quantify the molecular structure of SCP. After sulfation, the intensity of the C6 am peak at 62 ppm decreased, whereas the new peak at 69 ppm increased. The other peaks remained almost unchanged. The amount of sulfate at C6 increased with an increase in R value. Under the presence of sulfamic acid in low quantities during the sulfate reaction, sulfate groups are preferentially introduced into the hydroxyl groups at C2 and C3 of CP. For high quantities of sulfamic acid, the sulfate reactions occur at C2, C3, and C6. FT-IR spectroscopy confirmed that the hydroxide groups were mainly sulfated. This study demonstrates the importance of the substitution rate of the sulfated C6 in SCP to achieve ultra-high water retention in cellulose pulps, which is useful for the further development of the synthesis of chemically modified CPs. Declarations Competing Interests The authors have no conflicts of interest directly relevant to the content of this article. Compliance with Ethical Standards Not applicable. Funding The authors did not receive support from any organization for the submitted work. Author Contribution S.M. (Sakura Morimitsu) and K.Y. (Kazuhiko Yamada) conceived the concept of the study and created the experimental design. S.M. performed material preparation. All authors conducted the experiments and analyzed the data. The first draft of the manuscript was written by SM, AN (Ayato Nishimura), and KY. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Acknowledgement This work was supported by the "Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM)" of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT). References Atalla RH, VanderHart DL (1999) The role of solid state 13 C NMR spectroscopy in studies of the nature of native celluloses. Solid State Nucl Magn Reson 15:1–19. https://doi.org/10.1016/s0926-2040(99)00042-9 Foston M (2014) Advances in solid-state NMR of cellulose. 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Cite Share Download PDF Status: Published Journal Publication published 05 Jul, 2025 Read the published version in Cellulose → Version 1 posted Editorial decision: Revision requested 10 Nov, 2024 Reviews received at journal 10 Nov, 2024 Reviews received at journal 07 Nov, 2024 Reviewers agreed at journal 01 Nov, 2024 Reviews received at journal 31 Oct, 2024 Reviewers agreed at journal 31 Oct, 2024 Reviewers agreed at journal 31 Oct, 2024 Reviewers invited by journal 31 Oct, 2024 Editor assigned by journal 30 Oct, 2024 Submission checks completed at journal 21 Oct, 2024 First submitted to journal 24 Sep, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-5147146","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":376278227,"identity":"a883b2a8-86b4-43d3-85d9-6fdd5fbeb0a2","order_by":0,"name":"Sakura Morimitsu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYJACxgYgwQ/jsYFJHiK0SDaQrMXgALGO0m1gf/hxZts9eeNrh5995vlzOJqPgfnhAwaZOzi1mB3gMZbc2FZsuO12mvFs3rbDuW0MbMYGDDzPcGu5/4ZB8mFbAuO22wnGzLwNIC08bBIMPIfx2ML++CdQi/3m2emfmYEOI0YLgxnQYQmJG6RzjJl52IjSwmNmOeNcQvKM2znFjHPb0nPbmIF+ScDnF6DDbvaUJdj2z07fzPDmj3Xu/Pbmhw8+9uAOMSyAGYgTew6QogUMfpCuZRSMglEwCoYtAAAKnFJ51TobggAAAABJRU5ErkJggg==","orcid":"","institution":"Marusumi Paper Co., Ltd","correspondingAuthor":true,"prefix":"","firstName":"Sakura","middleName":"","lastName":"Morimitsu","suffix":""},{"id":376278228,"identity":"7b09ffbe-ac6d-4e5f-921b-dd3252885ca3","order_by":1,"name":"Ayato Nishimura","email":"","orcid":"","institution":"Marusumi Paper Co., Ltd","correspondingAuthor":false,"prefix":"","firstName":"Ayato","middleName":"","lastName":"Nishimura","suffix":""},{"id":376278229,"identity":"f8d029c2-8207-4e41-bf05-2b8ae549960f","order_by":2,"name":"Kenzo Deguchi","email":"","orcid":"","institution":"National Institute for Materials Science","correspondingAuthor":false,"prefix":"","firstName":"Kenzo","middleName":"","lastName":"Deguchi","suffix":""},{"id":376278230,"identity":"9f43af5e-0c8e-4c79-bc69-e2200de45c57","order_by":3,"name":"Yuuki Mogami","email":"","orcid":"","institution":"National Institute for Materials Science","correspondingAuthor":false,"prefix":"","firstName":"Yuuki","middleName":"","lastName":"Mogami","suffix":""},{"id":376278231,"identity":"2ec986ac-f255-4b55-bb49-d0ae8cec046a","order_by":4,"name":"Shinobu Ohki","email":"","orcid":"","institution":"National Institute for Materials Science","correspondingAuthor":false,"prefix":"","firstName":"Shinobu","middleName":"","lastName":"Ohki","suffix":""},{"id":376278232,"identity":"feebe563-7019-465a-ab88-cee093ce52fe","order_by":5,"name":"Kenjiro Hashi","email":"","orcid":"","institution":"National Institute for Materials Science","correspondingAuthor":false,"prefix":"","firstName":"Kenjiro","middleName":"","lastName":"Hashi","suffix":""},{"id":376278233,"identity":"19d66136-4849-4716-94f9-d5aed27af199","order_by":6,"name":"Atsushi Goto","email":"","orcid":"","institution":"National Institute for Materials Science","correspondingAuthor":false,"prefix":"","firstName":"Atsushi","middleName":"","lastName":"Goto","suffix":""},{"id":376278234,"identity":"3ecb2dd0-f7ff-49c2-9be2-ec5bc13ac802","order_by":7,"name":"Kazuhiko Yamada","email":"","orcid":"","institution":"Kochi University","correspondingAuthor":false,"prefix":"","firstName":"Kazuhiko","middleName":"","lastName":"Yamada","suffix":""}],"badges":[],"createdAt":"2024-09-24 18:23:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5147146/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5147146/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10570-025-06609-5","type":"published","date":"2025-07-05T15:58:08+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":69912544,"identity":"cf5baae3-0bc6-4da8-9017-c15e19ec075b","added_by":"auto","created_at":"2024-11-26 14:04:40","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":15346,"visible":true,"origin":"","legend":"\u003cp\u003eWater retention value of sulfated cellulose pulp (SCP) with different R values. Water retention value of sulfated cellulose pulp (SCP) with different molar ratios of sulfamic acid and cellulose pulp (R)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/9e12b19a15d4ab197376a6b5.png"},{"id":69910286,"identity":"51590086-73fc-482f-b494-528fb2928680","added_by":"auto","created_at":"2024-11-26 13:48:40","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":234863,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC CPMAS NMR spectrum of (a) CP and (b) SCP with an R value of 4.19\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/67d43590c9fa1c8667f758d2.jpeg"},{"id":69911734,"identity":"5c2ea527-5467-45aa-8b90-68026781d4ff","added_by":"auto","created_at":"2024-11-26 13:56:40","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":182236,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003csup\u003e13\u003c/sup\u003eC DDMAS NMR spectrum of SCP with an R value of (a) 0, (b) 1.05, (c) 2.09, (d) 3.14, and (e) 4.19\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/13f538353be37fdc1ff8917c.jpeg"},{"id":69910281,"identity":"63aea6b0-a1dd-4052-b8d7-2edf73aed2f5","added_by":"auto","created_at":"2024-11-26 13:48:40","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":164099,"visible":true,"origin":"","legend":"\u003cp\u003eDeconvolution of sulfated C6 in the \u003csup\u003e13\u003c/sup\u003eC DDMAS NMR spectra of SCP with R values of (a) 1.05 and (b) 4.19\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/ed96200bc60a95476881a6ce.jpeg"},{"id":69910280,"identity":"eb162045-69ed-47d4-96b3-4a1b0ad8a9c2","added_by":"auto","created_at":"2024-11-26 13:48:40","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":82206,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between the amount of sulfated groups at C6 and the R value\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/cdbd4e54f1be4d0081ba6b97.jpeg"},{"id":69911732,"identity":"adac7457-1dc5-4f87-98c7-c4ba48ddced0","added_by":"auto","created_at":"2024-11-26 13:56:40","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":77591,"visible":true,"origin":"","legend":"\u003cp\u003eAssociation between the amount of sulfate groups and the R value\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/e067a451890d3c889ffa19eb.jpeg"},{"id":69912545,"identity":"92224062-4a07-4a0b-8481-c04d802bb596","added_by":"auto","created_at":"2024-11-26 14:04:40","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":261581,"visible":true,"origin":"","legend":"\u003cp\u003eInfrared spectra of (a) CP and SCP with R values of (b) 0, (c) 1.05, (d) 2.09, (e) 3.14, and (f) 4.19\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/77ce9c8c86c35d3d2297767d.jpeg"},{"id":86179161,"identity":"108f9352-25f3-4bd6-8f9a-5e8f3342b706","added_by":"auto","created_at":"2025-07-07 16:16:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1529214,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5147146/v1/862d0e2f-91aa-4bb3-bdaf-21874afe7b2b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Sulfated cellulose pulp with ultra-high water retention characteristics","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSulfated cellulose pulp (SCP) has attracted considerable attention in recent years for its ability to produce cellulose nanofibers, which is a fiber isolated to the smallest unit that constitutes a cellulose fiber. Several synthetic methods for SCPs have been proposed, such as sulfuric acid hydrolysis (R\u0026aring;nby et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1949\u003c/span\u003e), the HSO\u003csub\u003e3\u003c/sub\u003eCl/(CH\u003csub\u003e3\u003c/sub\u003eCO)\u003csub\u003e2\u003c/sub\u003eO system (Zhang et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2011\u003c/span\u003ea), the sulfamic acid/urea/\u003cem\u003eN\u003c/em\u003e,\u003cem\u003eN\u003c/em\u003e-dimethylformamide system (Huang and Zhang \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), the HSO\u003csub\u003e3\u003c/sub\u003eCl/\u003cem\u003eN\u003c/em\u003e,\u003cem\u003eN\u003c/em\u003e-dimethylformamide system (Zhao MW et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), and the deep eutectic solvent system (DES, CP/sulfamic acid/urea system without water) (Sirvi\u0026ouml; et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Similar to those modified by carboxyl (Saito et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) and phosphate groups (Ghanadpour et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Noguchi et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), sulfated cellulose pulp is also defibrillated by mechanical treatment in a high-pressure homogenizer, resulting in nanofibers. Nanofibers have been applied to functional materials such as O\u003csub\u003e2\u003c/sub\u003e gas barrier films (Fukuzumi et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), rheology control agents (Wang et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), and metal ion adsorbents (Liu et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRecently, our group has presented the synthesis of SCP using a CP/sulfamic acid/urea system, affording a water retention value (WRV) of approximately 3000% (Nishimura and Otsuka 2023a), and enhanced water dispersion stability and transparency in aqueous dispersion (submitted). The mechanism by which SCP appears transparent in water has been discussed in terms of its fiber morphology and is attributed to the swollen fiber structure of the SCP fibers. However, its molecular structure has not been clarified yet.\u003c/p\u003e \u003cp\u003eStructural analyses are crucial for understanding the functions of SCPs. Solid-state \u003csup\u003e13\u003c/sup\u003eC nuclear magnetic resonance (NMR) is one of the best analytical approaches, providing structural information at the molecular level even for insoluble samples. The sulfate group of SCP was previously investigated using the \u003csup\u003e1\u003c/sup\u003eH-\u003csup\u003e13\u003c/sup\u003eC cross-polarization/magic angle spinning (CPMAS) method (Zhang et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2011\u003c/span\u003eb), indicating that the hydroxyl group at the C6 position of the cellulose pulp is involved in the sulfation reaction. CPMAS can provide useful structural information. However, it should be noted that this technique is not quantitative. Although the measurement time takes longer than CPMAS, direct polarization/magic angle spinning (DDMAS) is highly reliable in quantifiability because \u003csup\u003e13\u003c/sup\u003eC can be measured directly without passing through \u003csup\u003e1\u003c/sup\u003eH magnetization. To the best of our knowledge, no studies have reported \u003csup\u003e13\u003c/sup\u003eC DDMAS experiments on SCP. In this study, a novel SCP was synthesized using the CP/sulfamate/urea reaction system, exhibiting ultra-high water retention capacity. Furthermore, its water retention mechanisms are discussed based on the structural information obtained by \u003csup\u003e13\u003c/sup\u003eC DDMAS.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eThe cellulose pulp (CP) used in this study was never-dried softwood-bleached kraft pulp (Marusumi Paper Co., Ltd., Japan). The concentration of the CP slurry was adjusted to 25 wt%, and the water used for the CP slurry was replaced from industrial to pure water. Sulfamic acid (H\u003csub\u003e2\u003c/sub\u003eNSO\u003csub\u003e3\u003c/sub\u003eH), urea ((H\u003csub\u003e2\u003c/sub\u003eN)\u003csub\u003e2\u003c/sub\u003eC=O), sodium hydroxide (NaHCO\u003csub\u003e3\u003c/sub\u003e), and sodium hydrogen carbonate (NaOH) were purchased from FUJIFILM Wako Pure Chemical Co. All the materials were used without further purification. The ion-exchange resin was purchased from Organo Co., Japan. Pure water (distilled by Marusumi Paper Co., Ltd., Japan, conductivity\u0026thinsp;\u0026lt;\u0026thinsp;0.1 mS/m, pH 5\u0026ndash;8) was used in all the experiments.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSulfation of cellulose pulp\u003c/h3\u003e\n\u003cp\u003eThe sulfate reaction solution was prepared by adding and stirring S (1.25\u0026ndash;5.00 g, 0.013\u0026ndash;0.051 mol) and U (2.50 g, 0.042 mol) with pure water (12 g) at room temperature (296 K). The 25 wt% CP (8 g, BD2 g) was immersed in the sulfate reaction solution for 10 min, spread thinly and uniformly on an acrylic plate, and dried at 358 K for 3 h using a constant-temperature dryer (DKN602, Yamato Scientific Co. Japan). The dried CP reacted when heated to 413 K for 30 min. The reactants were neutralized with NaHCO3 and washed with pure water on a 330-mesh sieve (Sampo Co., Japan). The sulfated cellulose pulp slurry was adjusted to a concentration of 1.0 wt% with pure water and then refrigerated at 277 K. The reaction conditions were determined at 5 different molar ratios (R), where R was determined by dividing the number of moles of S by the number of moles of the anhydroglucose units in CP. The moles of anhydroglucose units were calculated from the dry weight of the pulp/162.\u003c/p\u003e\n\u003ch3\u003eWater retention value\u003c/h3\u003e\n\u003cp\u003eThe water retention value (WRV) was measured using the TAPPI method and 10 g of the 0.5 wt% SCP slurry. The SCP slurry was centrifuged at 3000 g for 15 min and the WRV was calculated using the following Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\text{W}\\text{R}\\text{V}\\left(\\text{%}\\right)=\\frac{Ww-Wd}{Wd}\\times\\:100\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eWw\u003c/em\u003e is the mass after centrifugation and \u003cem\u003eWd\u003c/em\u003e is the mass after drying the sample at 358 K for 24 h.\u003c/p\u003e\n\u003ch3\u003eSolid-state C NMR\u003c/h3\u003e\n\u003cp\u003eFreeze-dried SCP was powdered using a blender (WB-1; Osaka Chemical Co., Osaka, Japan). \u003csup\u003e1\u003c/sup\u003eH and \u003csup\u003e13\u003c/sup\u003eC NMR experiments were performed at 500.194 and 125.774 MHz, respectively, on an 11.7 T JEOL ECZ 500 spectrometer (JEOL, Tokyo, Japan) using a 4 mm magic-angle spinning (MAS) probe at room temperature. Potassium bromide was used to adjust the magic angle, and adamantane was used as the reference. Standard ramped cross-polarization (CP), direct-polarization (DD), and Torchia sequences (Torchia \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1978\u003c/span\u003e) were used with a MAS frequency of 15 kHz and high-power irradiation to achieve heteronuclear decoupling during each detection period. For \u003csup\u003e13\u003c/sup\u003eC CPMAS, the following parameters were used: π/2 for \u003csup\u003e1\u003c/sup\u003eH, 3.3 \u0026micro;s; mixing time, 5 ms; spectral width (SW), 400 ppm; data points (DP), 1024; recycle delay time (RD), 5 s; accumulations, 1000\u0026ndash;1200 scans. For \u003csup\u003e13\u003c/sup\u003eC DDMAS, the following parameters were used: π/2 for \u003csup\u003e13\u003c/sup\u003eC, 3.3 \u0026micro;s; RD, 1200 s; accumulations, 260\u0026ndash;300 scans; the other parameters were the same as those of \u003csup\u003e13\u003c/sup\u003eC CPMAS. For Torchia experiments of \u003cem\u003eT\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e measurements, the following parameters were used: RD, 4 s; accumulations, 700 scans; interval time, 1, 1.39, 1.95, 2.71, 3.79, 5.25, 7.37, 10.28, 14.34, 20.0, 50.0, 80.0, 125.0, and 200 s; the other parameters were the same as those of the \u003csup\u003e13\u003c/sup\u003eC CP/DDMAS experiments. All NMR spectra were processed and analyzed using DELTA software (JEOL USA, Inc.).\u003c/p\u003e\n\u003ch3\u003eConductometric titration of contents\u003c/h3\u003e\n\u003cp\u003eThe amount of sulfated groups of SCP was determined by conductometric titration (Nishimura and Otsuka 2023b). The 1.0 wt% SCP slurry was adjusted to a 0.2 wt% SCP slurry. The 0.2 wt% SCP slurry was added to an ion exchange resin (1.0 g) and stirred for 1 h. After stirring, the ion-exchange resin was removed from the 0.2 wt% SCP slurry using a filter. The 0.2 wt% SCP slurry was titrated by adding a small amount of 0.1M NaOH using a pipette. The amount of sulfate groups was estimated from the moles of 0.1 M NaOH required for neutralization.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eFourier-transform infrared spectroscopy\u003c/h2\u003e \u003cp\u003eThe Fourier-transform infrared (FTIR) spectra of CP and SCP were recorded on a Fourier transform infrared spectrometer (Shimadzu Corp., Japan) at the transmission mode, with a resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the WRV results of SCP for different R values. WRV increased slightly as the R value increased from 0 to 1.05, and increased almost linearly as the R value increased above 1.05. The maximum WRV reached approximately 16000% when the R value was 4.19, which is approximately 100 times greater than that of CP. Apart from a recent study reporting a WRV of 3000%, previous studies have shown that the WRV of TEMPO-oxidized CP is approximately 400% at about 1.5 mmol/g of carboxyl groups (Saito et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), while phosphorylated CP has a WRV of approximately 900% at about 1.9 mmol/g of phosphorus groups (Hou et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe molecular structure of SCP was investigated by solid-state \u003csup\u003e13\u003c/sup\u003eC NMR spectroscopy to elucidate the reason for the significant increase in WRV. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) shows the \u003csup\u003e13\u003c/sup\u003eC CPMAS NMR spectrum of CP with the spectral assignment based on the literature (Atalla and VanderHart \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Foston \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Solum \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). C6\u003csub\u003ecry\u003c/sub\u003e and C6\u003csub\u003eam\u003c/sub\u003e denote the crystalline and non-crystalline C6 signals, respectively. The C6\u003csub\u003eam\u003c/sub\u003e peak was observed at 62 ppm, the C6\u003csub\u003ecry\u003c/sub\u003e peak was at 65 ppm, the C2, 3, 5 carbon peaks were located between 70 and 78 ppm, the C4\u003csub\u003eam\u003c/sub\u003e peak was at 84 ppm, the C4\u003csub\u003ecry\u003c/sub\u003e carbon peak was at 89 ppm, and the C1 peak was at 105 ppm. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) shows the \u003csup\u003e13\u003c/sup\u003eC CPMAS NMR spectrum of SCP at R\u0026thinsp;=\u0026thinsp;4.19. A new peak was observed in the spectrum of SCP at 69 ppm, which was attributed to the sulfated C6 carbon (Zhang et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2011\u003c/span\u003eb). The intensities of the peaks increased as those of C6\u003csub\u003eam\u003c/sub\u003e decreased, confirming that C6\u003csub\u003eam\u003c/sub\u003e was involved in the reaction.\u003c/p\u003e \u003cp\u003eDDMAS method is valid for quantitative measurements of the above structural changes if RD is set to more than five times that of \u003cem\u003eT\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e. The longest \u003cem\u003eT\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e in CP, which is believed to be the same as that in SCP, was 163 s for C4\u003csub\u003ecry\u003c/sub\u003e. Under these experimental conditions, RD was set at 1200 s so that the intensity of each signal was guaranteed to be quantitative. Figure. 3 shows the solid-state \u003csup\u003e13\u003c/sup\u003eC DDMAS NMR spectra of the SCP with R values ranging from 0 to 4.19. The peak intensity derived from the sulfate groups of SCP at 69 ppm increased as the R value increased from 0 to 4.19. Furthermore, the C6\u003csub\u003eam\u003c/sub\u003e peak at 62 ppm decreased as R increased from 1.05 to 4.19, whereas the C6\u003csub\u003ecry\u003c/sub\u003e peak at 65 ppm did not exhibit any significant change. CP consists of alternating crystalline and non-crystalline regions (Wickholm et al. 2009). The crystalline region of CP was hardly accessible in the sulfated reaction because of its regularly lined and high-density composition. Moreover, the non-crystalline sections of CP are irregular and flexible, which enhances the reactivity of the chemicals (Yu and Wu \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Therefore, the C6\u003csub\u003eam\u003c/sub\u003e at 62 ppm was preferentially sulfated, while the other peaks remained virtually unchanged after the reaction.\u003c/p\u003e \u003cp\u003eQuantitative measurements of SCP focused on the peaks between 57 and 70 ppm regarding C6. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the deconvolution of sulfated C6 in the \u003csup\u003e13\u003c/sup\u003eC DDMAS NMR spectra of SCP with (a) R\u0026thinsp;=\u0026thinsp;1.05 and (b) R\u0026thinsp;=\u0026thinsp;4.19. Deconvolution of the signals was performed using Voigt functions. The percentage of C6 converted to sulfated C6 in CP was calculated by comparing the intensities of each peak. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the correlation between the amount of sulfated groups at C6 in SCP and the R values. The amount of sulfate groups increased as the R value increased from 1.05 to 2.09 and continued to increase slightly as the R value increased from 2.09 to 4.19. Sulfated C6 was almost absent when R\u0026thinsp;=\u0026thinsp;1.05. The maximum value of sulfated C6 was approximately 18% when R\u0026thinsp;=\u0026thinsp;4.19. These experimental results indicate that the amount of sulfated C6 plays a significant role in WRV. In the cellulose molecules, some hydroxyl groups extend outward onto the surface of the microfibrils. In the case of CP, some microfibrils are closely packed together via hydrogen bonds between the exposed hydroxyl groups. However, when the hydroxyl groups are replaced with polar sulfate groups, the sulfate reaction results in electron repulsion and steric hindrance. This increases WRV because space is created for water to enter.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the correlation between the entire content of the SCP sulfate groups determined by the electrical conductivity method and the R values. The total amount of sulfate groups increased from 0 to 1.33 mmol/g as the R value increased from 0 to 1.05, and continues to increased slightly from 1.35 to 1.91 mmol/g as the R value increased from 2.09 to 4.19. The maximum total amount of sulfate groups reaches 1.91 mmol/g when R\u0026thinsp;=\u0026thinsp;4.19, which is nearly equivalent to that of the amount of modifiable hydroxyl groups of C6 present on the surface of microfibrils (Isogai \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Additionally, although the sulfated C6 was almost absent when R was 1.05 (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), the sulfate groups content was 1.33 mmol/g. Such results indicate that sulfate groups are mainly introduced to the hydroxyl groups at the C2 and C3 positions of CP in the sulfation reaction when the concentration of sulfamic acid is low. When the concentration is high, sulfate groups are introduced into the hydroxyl groups at C6. The steric hindrance of the C6 primary hydroxyls is greater than that of the secondary hydroxyls of C2 and C3. Therefore, SCP has more spaces where water can enter, causing a significant increase in WRV when R is above 1.05.\u003c/p\u003e \u003cp\u003eFourier-transform infrared spectroscopy was used to verify the sulfation of the hydroxyl groups in CP. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the infrared spectra of (a) CP and SCP with R values of (b) 0, (c) 1.05, (d) 2.09, (e) 3.14, and (f) 4.19. The intensity of the peaks at 810 and 1230 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e gradually increased as the R value increased. The peak at 810 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to S\u0026thinsp;=\u0026thinsp;O vibrations and that at 1230 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to C-O-S vibrations. However, S\u0026thinsp;=\u0026thinsp;O and C-O-S vibrations were almost nonexistent in the spectra of CP and SCP with R\u0026thinsp;=\u0026thinsp;0. Therefore, urea is not directly involved in the sulfate reaction of CP, supporting the preferential sulfation of hydrogen groups.\u003c/p\u003e "},{"header":"Conclusions","content":"\u003cp\u003eA novel SCP was developed using a sulfate reaction with CP, exhibiting a WRV of 16000% for R\u0026thinsp;=\u0026thinsp;4, which was 100 times greater than that of CP. Solid-state \u003csup\u003e13\u003c/sup\u003eC NMR was used to investigate and quantify the molecular structure of SCP. After sulfation, the intensity of the C6\u003csub\u003eam\u003c/sub\u003e peak at 62 ppm decreased, whereas the new peak at 69 ppm increased. The other peaks remained almost unchanged. The amount of sulfate at C6 increased with an increase in R value. Under the presence of sulfamic acid in low quantities during the sulfate reaction, sulfate groups are preferentially introduced into the hydroxyl groups at C2 and C3 of CP. For high quantities of sulfamic acid, the sulfate reactions occur at C2, C3, and C6. FT-IR spectroscopy confirmed that the hydroxide groups were mainly sulfated. This study demonstrates the importance of the substitution rate of the sulfated C6 in SCP to achieve ultra-high water retention in cellulose pulps, which is useful for the further development of the synthesis of chemically modified CPs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting Interests\u003c/h2\u003e \u003cp\u003eThe authors have no conflicts of interest directly relevant to the content of this article.\u003c/p\u003e \u003ch2\u003eCompliance with Ethical Standards\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe authors did not receive support from any organization for the submitted work.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eS.M. (Sakura Morimitsu) and K.Y. (Kazuhiko Yamada) conceived the concept of the study and created the experimental design. S.M. performed material preparation. All authors conducted the experiments and analyzed the data. The first draft of the manuscript was written by SM, AN (Ayato Nishimura), and KY. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis work was supported by the \"Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM)\" of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAtalla RH, VanderHart DL (1999) The role of solid state \u003csup\u003e13\u003c/sup\u003eC NMR spectroscopy in studies of the nature of native celluloses. 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Int J Biol Macromol 41:376\u0026ndash;382. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijbiomac.2007.05.007\u003c/span\u003e\u003cspan address=\"10.1016/j.ijbiomac.2007.05.007\" 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":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Cellulose, Sulfated cellulose pulp, Water retention, Solid-state 13C NMR, Sulfate group","lastPublishedDoi":"10.21203/rs.3.rs-5147146/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5147146/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA sulfated cellulose pulp (SCP) exhibiting ultra-high water retention properties, has been developed and its water retention mechanisms have been analyzed based on its molecular structure determined by solid-state \u003csup\u003e13\u003c/sup\u003eC nuclear magnetic resonance (NMR). Cellulose pulp (CP) wood-derived was sulfated using sulfamic acid and urea reaction system with varying concentrations of sulfamic acid. SCP has 1.31\u0026ndash;1.91 mmol/g of sulfate groups and exhibits a high water retention value (WRV) of 16000%, which is approximately 100 times greater than that of CP. After the sulfate reaction, a new peak at 69 ppm was observed in the solid-state \u003csup\u003e13\u003c/sup\u003eC NMR spectrum, which was assigned to the sulfated C6. Quantitative analysis indicated that approximately 18% of C6 in CP was converted to sulfated C6. WRV increased almost linearly with the amount of sulfated C6, which played an important role in the water retention capacity. SCP was proven very promising as a novel functional material, owing to the molecular mechanisms involved.\u003c/p\u003e","manuscriptTitle":"Sulfated cellulose pulp with ultra-high water retention characteristics","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-26 13:48:35","doi":"10.21203/rs.3.rs-5147146/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-11-10T16:17:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-10T13:02:12+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-07T18:03:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"281269614302985302049279886386797495837","date":"2024-11-01T11:53:11+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-01T01:53:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"100548545399752693606931632320687051329","date":"2024-11-01T00:43:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"243642470998102362883349404132992960047","date":"2024-10-31T16:03:43+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-31T15:26:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-30T18:31:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-21T08:22:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"Cellulose","date":"2024-09-24T18:21:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"591e4dba-ff5a-41ed-a0ce-5a84cf0708b5","owner":[],"postedDate":"November 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-07T16:05:27+00:00","versionOfRecord":{"articleIdentity":"rs-5147146","link":"https://doi.org/10.1007/s10570-025-06609-5","journal":{"identity":"cellulose","isVorOnly":false,"title":"Cellulose"},"publishedOn":"2025-07-05 15:58:08","publishedOnDateReadable":"July 5th, 2025"},"versionCreatedAt":"2024-11-26 13:48:35","video":"","vorDoi":"10.1007/s10570-025-06609-5","vorDoiUrl":"https://doi.org/10.1007/s10570-025-06609-5","workflowStages":[]},"version":"v1","identity":"rs-5147146","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5147146","identity":"rs-5147146","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}