Starch-cellulose-gelatin hydrogels obtained by reactive extrusion aiming an ecologically friendly perspective

Starch-cellulose-gelatin hydrogels obtained by reactive extrusion aiming an ecologically friendly perspective | 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 Starch-cellulose-gelatin hydrogels obtained by reactive extrusion aiming an ecologically friendly perspective BEATRIZ MARIM, Jessica Pereira, Avacir Andrello, Suzana Mali This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3755080/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 Biopolymeric hydrogels represent a versatile class of materials with a wide range of potential applications, including their use in agricultural materials, drug delivery systems, biosensors, and food packaging. This investigation primarily centered on the synthesis and characterization of biodegradable hydrogels based on starch, cellulose, and gelatin, acting as a polymeric matrix intended for water retention in agricultural contexts. Prior to their incorporation into the hydrogels formulations, cassava starch and cellulose extracted from oat hulls underwent modification via reactive extrusion involving reaction with citric acid (CA) and sodium trimetaphosfate (STMP) as crosslinking agents, respectively. The hydrogels were obtained through a reactive extrusion process to produce porous pellets. These pellets were characterized according to their porosity, thermal properties, degree of swelling at different times and pHs, and water adsorption capacities. The hydrogel sample formulated with both CA-modified starch and STMP-modified cellulose, and gelatin, presented the highest values of porosity (> 45%) and open pores (> 5%), and the higher degree of swelling (607%). These materials as promising candidates for application in agriculture to increase water and/or fertilizers retention capacity in soil, with important advantages, including their biodegradability and low toxicity. It is worth mentioning that the reactive extrusion process used is a continuous process, with low effluent generation and scalable for large-scale production. Biopolymers Porosity Swelling Microstructure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Hydrogels have a three-dimensional structure with hydrophilic functional groups covalently bonded to the polymer main chain, endowing them with the capability to absorb water and swell, while maintaining structural integrity without dissolution. This stability in the presence of water is attributed to the intermolecular crosslinks within the three-dimensional polymeric network. In their desiccated state, hidrogels exhibit brittleness, but upon contact with water, they undergo a reversible transformation into an elastic gel, retaining their original configuration [ 1 – 7 ]. There are several applications for these materials, such as agriculture, pharmaceuticals, biomedical, hygiene products, effluent treatment and biosensors, and they are being widely applied in agriculture to increase the retention capacity of water and fertilizers in the soil, reducing the frequency of irrigation. In addition, these hydrogels have been used as seed coatings and root dips to aid germination and improve their habitability [ 7 , 8 ]. Polyacrylamide or polyacrylic acid are largely reported in literature as synthetic polymers that result in high performance hydrogels [ 5 , 9 – 12 ], however these polymers are non-biodegradable and obtained from non-renewable sources [ 13 ]. Recently, several hydrophilic biopolymers are being extensively studied for the production of hydrogels, and hydrogels consisting of a mixture of polymers are highlighted because there is greater interaction between chains of different structures, improving the characteristics of the material, thus the application of the hydrogel is expanded [ 14 – 17 ]. Starch, gelatin and cellulose are considered interesting raw materials for the obtainment of hydrogels, these materials present numerous possibilities of chemical and physical modifications described in the literature, and also had several advantages, including its non-toxicity, biodegradability, biocompatibility, low cost, and wide availability. Additionally, they are listed as generally recognized as safe (GRAS) and included in the Food and Drug Administration Inactive Ingredient Guide [ 18 , 19 ]. According to Gopinath et al. [ 15 ], chemically modified cellulose and starch derivatives have been emerged as potential raw materials for obtainment of new hydrogels formulations. Generally, the most employed crosslinking agents for biopolymeric hydrogels based on starch, cellulose and gelatin are epichlorohydrin and glutaraldehyde, however they are toxic compounds and are not environmentally friendly [ 20 ]. Recently, an increased interest was observed in the use of low toxicity crosslinking agents such as citric acid (CA) or sodium trimetaphosphate (STMP) to obtain new hydrogels formulations, especially for natural polymer-based hydrogels [ 21 , 22 ]. Reactive extrusion can be used for biopolymers modification and also for hydrogels production and recent research reports the effectiveness of this technology. Cagnin et al. [ 23 , 24 ] reported the production of hydrogels based on carboxymetilcellulose and starch by reactive extrusion using STMP as a crosslink agent. Simões et al. [ 25 ] reported the use of reactive extrusion for the obtainment of hydrogels based on starch and xanthan gum using CA as a crosslinker. This study aimed the production and characterization of biodegradable hydrogels using a mixture of starch, cellulose and gelatin as a polymeric matrix to be used as a potential water reservoir on agricultural systems by using an ecologically friendly perspective. Before being incorporated to the hydrogels formulations, cassava starch and cellulose were modified by reactive extrusion though reaction with CA and STMP, respectively, which were employed as green crosslinking agents. Subsequently, the hydrogels were produced by reactive extrusion as porous pellets, and they were characterized according to their porosity, thermal properties, degree of swelling at different times and pHs, and water adsorption capacities. Material and Methods Materials The hydrogel formulations were prepared with: 1) cassava starch (20% amylose and 80% amylopectin) purchased from Pinduca Co. Ltd. (Araruna, Brazil); 2) cellulose extracted from oat hulls using peracetic acid as a bleaching agent by the methodology described by Marim et al. [ 26 ]; and 3) gelatin (Biotec, São Paulo, Brazil). Glycerol (Synth) were employed as plasticizer and, citric acid (Synthlab, Diadema, Brazil) and sodium trimetaphosphate (Sigma Aldrich, St. Louis, USA) were employed to obtain modified starch and cellulose, respectively. Methods Modification of cellulose and starch by reactive extrusion CA (20% - g acid/100 g starch) and STMP (0.1% - g STMP/100 g cellulose) were employed to obtain the modified cassava starch and cellulose from oat hull, respectively, based on method described by Gil-Giraldo et al. [ 21 ]. The samples were prepared by dissolving different proportions of CA or STMP in distilled water, and the obtained solutions were mixed with starch and cellulose, respectively, resulting in samples with a final moisture content of 32% (g/g), which remained in sealed plastic bags at room temperature for 1h before extrusion. Starch and cellulose were extruded separately in a single screw extruder (AX Plastics, Diadema, Brazil) with a screw diameter of 1.6 cm and a screw length/screw diameter ratio (L / D) of 40, with four zones of heating and a matrix of 0.8 cm in diameter. The temperature in all zones was 100°C and the screw speed was 60 rpm. The starch and cellulose extrudates were collected, placed in an oven, dried to constant weight at 45°C, ground, and sieved in an 80-mesh sieve. Samples were washed three times with absolute ethanol to remove unreacted CA or STMP. Finally, the washed samples were air-dried at 45°C. Degree of substitution (DS) of modified starch was calculated according to Volkert et al. [ 27 ] by titration. For modified cellulose, the phosphorus content (%) was analyzed in triplicate by colorimetry in 600 nm (spectrophotometer Varian - Cary 50 Conc, São Paulo, Brazil) and DS was calculated as follows [ 24 ]: DS = 162*P/ (3100 − 102*P), where: P is phosphorus content (%); 162 is the molecular weight of the monomeric unit of cellulose, 3100 is the atomic weight of phosphorus multiplied by 100; and 102 is the group phosphate weight. Hydrogels production Four formulations (Table 1 ) were employed to obtain the biopolymeric hydrogels by reactive extrusion using different proportions of native and modified starch, cellulose and modified cellulose, and these proportions were determined by preliminary tests (data not presented), the formulations that were used were those that resulted in intact and easily processable pellets during the extrusion process. Gelatin and glycerol concentrations were fixed. The formulations were prepared by manually mixing the components with 35% glycerol, used as a plasticizer. The final mixtures were processed in a laboratory single-screw extruder (model EL-25, BGM, São Paulo, Brazil) with a screw diameter (D) of 25 mm and a with a screw diameter (D) of 25 mm, a screw length of 26D, using a die with six 2 mm diameter holes. Barrel temperature profile was 90/120/130/115⁰ C, from the feed zone to the die zone, and a screw speed of 35 rpm was employed. Subsequently, the samples were pelleted dried in a circulation oven at 60° C for 3 h and used for characterization. Table 1 Formulations used in the preparation of 100 g of hydrogels by reactive extrusion Components (g/100 g) Formulations S-C-G S-MC-G S.MS-C-G S.MS-MC-G Native starch (S) 51.0 51.0 30.6 30.6 Modified starch (MS) - - 20.6 20.6 Unmodified cellulose (C) 7.0 - 7.0 - Modified cellulose (MC) - 7.0 - 7.0 Gelatin (G) 7.0 7.0 7.0 7.0 Glycerol 35.0 35.0 35.0 35.0 Microtomography and Porosity An X-ray computed tomography (X-ray CT) was performed in a SkyScan-Bruker equipment (model 1172 MCT, Kontich, Belgium) to determine the porosity and pore size of the different hydrogel samples, in addition to presenting the image of the distribution of pores in each sample, performed in 3D. These tests were performed in triplicate. Fourier Transform-Infrared Spectroscopy (FT-IR) Approximately 1 mg of each sample were pulverized, dried and mixed with potassium bromide (KBr) and compressed into tablets in a mass ratio of approximately 1:100 (sample to KBr). FT-IR spectroscopy for the samples was performed with a Shimadzu FT-IR -8300 spectrometer (Kyoto, Japan), the scanning range was 4000 to 500 cm − 1 with spectral resolution of 4 cm − 1 . Thermal properties Thermogravimetric Analysis (TGA) of the samples were be performed using the Shimadzu TGA-50 (Japan) equipment. The scans were be performed at room temperature up to 600°C with a heating rate of 20°C/min under a nitrogen flow of 20 mL/min. Water adsorption isotherms The samples (0.5 g) were dried for 7 days in a desiccator containing anhydrous calcium chloride, and then they were placed at 25°C for 7 days in desiccators containing different saturated salt solutions providing specific water activities (aw) for the samples (0.11, 0.33, 0.43, 0.60, 0.75, and 0.90). Samples were dried at 105°C in a ventilated oven (035 Marconi MA, Piracicaba, Brazil) to determine their equilibrium moisture content at each aw condition. The GAB model (Guggenheim– Anderson-de Boer) was used to fit the sorption isotherm data, and the monolayer values were calculated from the GAB isothermal model [ 28 ] as follows: M = (m 0 CK aw ) / (1 − K aw ) (1 − K aw + CK aw ), where M is the equilibrium moisture (g water / 100 g solids), aw is the water activity, m 0 is the monolayer value (g water / 100 g solids), and C and K are GAB constants. Degree of swelling at different times and different pHs Degree of swelling was determined by gravimetric method using previously weighed cylindrical devices (3.0 x 3.5 cm) containing at one end a screen with a nominal opening of 138 x 75 mm, as described by Pereira, Lonni and Mali [ 29 ]. About 1g of each sample was weighed and placed inside the devices and then immersed in 10 mL of a different pH solution (4.0, 7.0 and 9.0) at 25°C. At predetermined times (30min, 24h and 48h), the devices containing the hydrogel pellets were removed from the solutions, the excess was removed with filter paper and then weighed. From the value obtained, the degree of swelling (g/g) of each sample was calculated in relation to its initial dry weight. Analyzes were performed in triplicate. Statistical analysis Analyses of variance (ANOVA) and Tukey's mean comparison test (p ≤ 0.05) were performed with Statistica software version 7.0 (Statsoft, OK, USA). Results and Discussion Modification of starch and cellulose Cassava starch was modified by reactive extrusion, and degree of substitution (DS) was 0.365 for CA-modified starch. Citric acid (C₆H₈O₇) is a tricarboxylic acid that acts as an esterifying agent for starch, but also as crosslinker agent, which results in increased stability of biopolymeric matrix [ 25 , 30 ]. Ye et al. [ 31 ] modified rice starch by reactive extrusion with CA and observed DS between 0.037 and 0.138 when the CA levels ranged from 10 to 40% (g CA/100 g starch). Regarding to the STMP-modified cellulose sample, the DS was 0.01. DS can be consider a good indicative of the occurrence of crosslinking of the phosphate groups grafted onto the polysaccharides chain [ 23 , 32 , 33 ]. The value observed in this study was lower when compared to DS reported by Cagnin et al.[ 23 , 24 ], who reported DS values of 0.05 for hydrogels obtained by reactive extrusion from cassava starch and carboxymethylcellulose crosslinked with STMP (4 g/100 g). Crosslinking agents as CA and STMP are capable of forming ester intermolecular linkages between specific groups on starch and cellulose molecules, and depending on the level of substitution, the polymer network is reinforced and results in changes in solubility and degree of swelling power [ 6 , 33 , 34 ], and according to Golachowski et al. [ 34 ], these changes are directly correlated with the degree of substitution. Additionally, CA and STMP were employed in this study because they are considered low toxicity crosslinking agents [ 21 , 22 ] in comparison to epichlorohydrin and glutaraldehyde, which are toxic compounds and are not environmentally friendly [ 20 ], and conventionally employed as crosslinking agents in starch, cellulose and gelatin hydrogels. Microtomography and Porosity The S-C-G sample showed the lowest porosity compared to the other samples (34.99%, Table 2 ), whereas the S.MS-MC-G sample prepared with modified starch and modified cellulose showed the highest porosity values (47.34%, Table 2 ) and a significant quantity of open pores (342.11%). Possibly, the modification of starch and cellulose resulted in a more expandable polymer matrix due to the introduction of new bonds between the polymeric chains. This led to a more stable melt that expanded upon exiting thef the extruder, mainting the porous structure of the material. As observed by Almeida et al. [ 35 ] the addition of starch to pectin hydrogels can enhance the three-dimensional network of the hydrogel, increasing the quantity of closed pores and resulting in a more compact and cohesive network. Table 2 Porosity, open pores, and closed pores of samples. Samples Porosity (%) Open Pores (%) Closed Pores (%) S-C-G 34.99 ± 0.03b 34.33 ± 1.28b 0.82 ± 0.31a S-MC-G 37.14 ± 0.14a,b 36.42 ± 1.52b 1.12 ± 0.02a,b S.MS-C-G 35.22 ± 0.09b 30.49 ± 1.09b 5.25 ± 1.99b,c S.MS-MC-G 47.34 ± 0.10a 42.11 ± 1.19a 5.53 ± 1.05c S-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin). Data are the means of replicate determinations ± standard deviation. Different letters in the same column indicate significant differences (p ≤ 0.05) between means (Tukey test). During reactive extrusion, high temperatures induce rapid evaporation leading to the formation of pores as water leaves the molten material. Evaporation is influenced by the material´s resistance to the pressure exerted by water vapor, along with extrusion process variables such as temperature and screw speed [ 36 ]. While these variables typically increase hydrogel porosity, in this study, the same conditions were standardized for all samples, attributing differences in results to formulation components. Cagnin et al. [ 24 ] reported lower porosity values (below 11%) for carboxymethylcellulose and starch hydrogels obtained by reactive extrusion using STMP as a crosslinking agent, highlighting the influence of raw materials and processing conditions. Porous material produced by extrusion typically displays irregular pore size [ 23 , 24 , 36 ]. The microtomography presented in Fig. 1 shows images of the S-C-G and S.MS-MC-G samples with the lowest and highest porosity values (Table 2 ). It is observed that in the S-C-G sample, the pores are small and uniformly distributed throughout the pellet, while in the S.MS-MC-G sample, there is a greater quantity of pores and open pores. The addition of modified starch and modified cellulose may have accelerated water evaporation from the material, leading to the formation of open pores in the pellets. Maaloul et al. [ 36 ] demonstrated that the addition of STMP resulted in hydrogels with open pores and interconnected irregular cavities, causing a higher quantity of open pores compared to the other samples. Porous hydrogels enhance water absorption through capillary forces, with open pores providing the hydrogel the ability to absorb water rapidly, regardless of size in the dry state. These open pores establish communication channels with the external environment, improving the expansion properties of the hydrogel [ 37 ]. On the other hand, hydrogels with a higher quantity of closed pores are relevant for mechanical strength and elasticity, applicable in situations requiring high mechanical resistance properties, such as in agricultural applications when the hydrogel is applied in deep soil and needs to withstand associated pressures. These hydrogels can also be employed in situations where water absorption rate is not a primary concern [ 35 , 36 ]. Fourier Transform-Infrared Spectroscopy (FT-IR) As seen in Fig. 2 a, a new important band at 1730 cm − 1 appeared in modified starch (MS) sample, it was attributed to the stretching vibration of the carbonyl ester group, indicating that the ester bonds were formed successfully. These results agreed with those presented by other authors [ 6 , 38 – 40 ], who used CA as esterifying and crosslinking agent for starch modification. FT-IR spectra of hydrogel samples are shown in Fig. 2 b. It was possible to identify an important band at 1730 cm − 1 , in the samples that were prepared with modified starch (S.MS-C-G and S.MS-MC-G), attributed to the stretching vibration of the carbonyl ester group, which provides evidence of ester bonds formed in the CA-modified starch used to prepare the hydrogels Other bands are observed in the FT-IR spectra (Fig. 2 b) of all hydrogels samples: a broad band at 3400 cm − 1 attributed to stretching of OH stretching in hydrogen bonds; a band at 2900 cm − 1 that was associated CH group stretching vibration (CH 2 groups) [ 26 , 40 ]. The characteristic e bands of cellulose were also distinguished at 1017 cm − 1 (C–O–C pyranose ring vibration) and 895 cm − 1 (β-glycosidic bond bending) [ 36 ]. Specific bands of the phosphate groups at 1214 cm − 1 (P = O elongation), 1129 cm − 1 (symmetric and asymmetric stretching of the PO 2 group), and 889 cm − 1 (PO bond) (Fig. 2 b) appeared in all hydrogels samples without any difference in intensity or shift, including the sample prepared with STMP-modified cellulose (S.MS-MC-G). This occurred probably due to the low concentration of STMP used, and additionally these bands may be covered by other bands between 1200 and 800 cm − 1 , which is characteristic of starch and cellulose [ 41 , 42 ]. Some authors reported that they did not detect these phosphate bands in crosslinked STMP starch and cellulose, and they attributed this to the low concentration of phosphate groups [ 36 , 39 ]. Khan et al. [ 5 ] reported that pure gelatin presents characteristics bands at 3430 cm − 1 due to amide –N–H elongation and at 1670 cm − 1 due to amine groups. It can be seen that in all hydrogels samples (Fig. 2 b) da band at 1650 cm − 1 , which can be an indicative of the formation of hydrogen bonds between OH groups of starch and cellulose with amine groups of gelatin [ 43 ]. Lu et al. [ 44 ] also reported that free carboxylic groups of gelatin can be esterified with hydroxyl groups of other polymers, such as cellulose and starch. Thermal properties TGA and DTGA curves are shown in Fig. 3 . For all hydrogel samples, the main weight loss occurred between 320 to 330°C, (Fig. 3 ), which can be associated with the degradation of starch and cellulose [ 19 , 42 ], and other peaks were observed at 160°C. These results are interesting results, indicating that the obtained hydrogels can support up to a temperature of 300°C without being significantly degraded. Rodríguez-Castellanos et al. [ 19 ] produced starch - gelatin hydrogels reinforced with cellulose by reactive extrusion, and they described that the weight loss observed at 160–170°C may be associated with the glycerol content in the polymer matrix, while the peaks at 266°C were associated to the degradation of long chains of gelatin. The peaks observed at 490°C indicate denaturation of the gelatin. Moisture sorption isotherms The moisture sorption isotherms and parameters of the GAB model are shown in Fig. 4 and Table 3 , respectively. All samples had a similar shape characteristic of hydrophilic materials and most starch and cellulose based materials [ 43 ] which means that hydrogels produced by reactive extrusion have a high affinity for water when exposed to high activity of water (a w ). The GAB model was efficient to describe the moisture sorption isotherms of the hydrogel samples (R2 = 0.99). The sorption isotherms of all samples showed similar patterns, with an increase in water activity (aw) when there was observed an increase in equilibrium moisture contents. The monolayer value (m 0 ) indicates the maximum amount of water adsorbed in a single layer per gram of dry material that can be related to the sorption sites [ 21 , 26 ]. According to the parameters presented in Table 1 , the sample produced with native starch and unmodified cellulose had the highest m 0 (53.25/100g) while samples prepared with modified starch had the lowest values (S.MS-C-G and S.MS-MC-G). These results indicate that the addition of modified starch in the samples decreased their capacity of adsorb water when stored in environments with higher relative humidities. Possibly, starch modification with CA resulted in a reinforced polymeric matrix, when free hydroxyl groups of starch were esterified, which resulted in a lower ability to interact with water. The parameter k is related to the heat of sorption of the multilayer region and, generally, the values of this parameter are less than 1, and the values of k ranged from 0.46 (S-C/G) and 3.59 (S.MS-C-G), respectively (Table 3 ). The parameter C is related to the sorption heat of the first layer, 0.58 to 0.88 (S.MS-C-/G and S.MS-MC-G). Table 3 GAB model parameters of hydrogels Samples m0 C K R2 S-C-G 53.25 0.46 0.58 0.99 S-MC-G 39.92 0.62 0.59 0.99 S.MS-C-G 5.86 3.59 0.88 0.99 S.MS-MC-G 6.51 2.41 0.88 0.99 S-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin). GAB model: M = (m 0 CKaw)/(1 − Ka w ) (1 − Ka w + CKa w ), where M is the equilibrium moisture (g water/100 g solids), a w is the water activity, m 0 is the monolayer value (g water/100 g solids), and C and K are GAB constants Degree of swelling at different times and pHs The effects of time and pH on the degree of swelling of hydrogels obtained by reactive extrusion can be seen in Figs. 5 and 6 and the effect of pH after 48 h of contact with water can be seen on Table 4 . A first visual analysis was performed to determine how long the granules could be immersed in distilled water without losing their structure. This criterion was established with a focus on the possible future application of hydrogel pellets, for which structural integrity is critical. However, all samples could remain submerged in water for more than 48h without dissolving or lose their shape. In Fig. 5 it was possible to observe the intact and swollen pellets after 48 immersed in water. In Fig. 6 it can be observed that the swelling of hydrogels pellet increased rapidly after 30 min of contact with water, but after 24 h the swelling degree stabilizes. Chemical and physical forces induce the liquid in a polymeric matrix, being responsible for the swelling of hydrogels. In the beginning there is rapid sorption of water, as there is a lot of free space between the chains, then the absorption rate decreases, as the molecules cannot bind at the crosslinking points, which act as barriers, bringing the material to equilibrium. The time required for the hydrogel to equilibrate depends on the crosslink density, extent of porosity and chemical composition, which determine characteristics such as hydrophilicity, charge and intermolecular interactions [ 35 , 42 , 45 – 47 ]. In Table 4 it was observed that there was no significant difference between the degree of swelling of the different hydrogels samples at pH 7 after 48 h immersed in water, except for sample S.MS-MC-G that presented the higher significantly value (6.07 g/g). This sample, which was formulated with both CA-modified starch and STMP-modified cellulose, also presented the highest values of porosity and open pores, which favored water absorption in this sample. Modification of starch and cellulose resulted in the introduction of new linkages between polymeric chains. When samples were subjected to pH 4 and pH 9, small variations were observed in the different formulations, however it was difficult to related these variation to hydrogels formulations. Table 4 Degree of swelling of hydrogel samples for 48 h at different pH values Samples Degree of Swelling (g/g) pH 4 pH 7 pH9 S-C-G 5.27 ± 0.03 aA 5.34 ± 0.05 bA 4.21 ± 0.25 abB S-MC-G 5.04 ± 0.14 baA 5.63 ± 0.12 bA 3.22 ± 0.05 bB S.MS-C-G 4.42 ± 0.09 bB 5.43 ± 0.59 bA 4.65 ± 0.07 abB S.MS-MC-G 4.13 ± 0.10 bB 6.07 ± 0.11 aA 3.74 ± 0.53 bB S-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin). Data are the means of replicate determinations ± standard deviation. Different small letters in the same column indicate significant differences (p ≤ 0.05) between means, and different capital letters in the same line indicate significant differences (p ≤ 0.05) between means (Tukey test). Comparing the effect of pH on degree of swelling of hydrogels samples, it can be observed that the highest values were observed for all samples at pH 7, with values ranging from 5.37 to 6.07 g/g (537–607% of swelling), however in pH 9 degree of swelling decreased for all samples (Table 4 ). According to Khan et al. [ 5 ], when the water absorption content can exceed more than 95 percent of the total weight or volume of the hydrogel, these hydrogels can be referred to as superabsorbent hydrogels, thus, the hydrogels obtained in this study can be considered as superabsorbent hydrogels, which in the most important property in a material that will be used for water retention on agricultural systems. CONCLUSION Reactive extrusion process was efficient to produce hydrogels based on citric acid-modified starch, STMP-modified cellulose and gelatin. After 48 h soaked in pH 7, they obtained higher values of degree of swelling (up to 530%), and the hydrogel sample formulated with both CA-modified starch and STMP-modified cellulose presented the highest values of porosity (> 45%) and open pores (> 5%), and the higher degree of swelling (607%), which makes these materials potential candidates for application as water retainers on agricultural systems, with important advantages, including their biodegradability, low toxicity and low environmental impact resulting from their production process. Additionally, it is worth mentioning that the reactive extrusion process used is a continuous process, with low effluent generation and scalable for large-scale production. Declarations Author Contribution Marim B.M. and Mali S. authored the main text of the manuscript, while Andrello prepared Figure 1 and Table 2. 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Eur Polym J 73:335–343. https://doi.org/10.1016/j.eurpolymj.2015.10.029 Khan F, Atif M, Haseen M, et al (2022) Synthesis, classification and properties of hydrogels: Their applications in drug delivery and agriculture. J Mater Chem B 10:170–203. https://doi.org/10.1039/d1tb01345a Gil Giraldo GA, Mantovan J, Marim BM, et al (2021) Surface Modification of Cellulose from Oat Hull with Citric Acid Using Ultrasonication and Reactive Extrusion Assisted Processes. Polysaccharides 2:218–233. https://doi.org/10.3390/polysaccharides2020015 Zhu S, Wang X, Cong Y, et al (2021) Free Radical Polymerization of Gold Nanoclusters and Hydrogels for Cell Capture and Light-Controlled Release. ACS Appl Mater Interfaces 13:19360–19368. https://doi.org/10.1021/acsami.1c03587 Cagnin C, Simões BM, Yamashita F, et al (2021) pH sensitive phosphate crosslinked films of starch-carboxymethyl cellulose. Polym Eng Sci 61:388–396. https://doi.org/10.1002/pen.25582 Cagnin C, Simões BM (2020) Hydrogels of starch / carboxymethyl cellulose crosslinked with sodium trimetaphosphate via reactive extrusion. 1–12. https://doi.org/10.1002/app.50194 Simões BM, Cagnin C, Yamashita F, Bonametti J (2019) Citric acid as crosslinking agent in starch/xanthan gum hydrogels produced by extrusion and thermopressing. LWT - Food Sci Technol 108950. https://doi.org/10.1016/j.lwt.2019.108950 Marim BM, Mantovan J, Giraldo GAG, Mali S (2020) Environmentally friendly process based on a combination of ultrasound and peracetic acid treatment to obtain cellulose from orange bagasse. J Chem Technol Biotechnol. https://doi.org/10.1002/jctb.6576 Volkert B, Lehmann A, Greco T, Nejad MH (2010) A comparison of different synthesis routes for starch acetates and the resulting mechanical properties. 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Food Hydrocoll 92:135–142. https://doi.org/10.1016/j.foodhyd.2019.01.064 Dong H, Vasanthan T (2020) Amylase resistance of corn, faba bean, and field pea starches as influenced by three different phosphorylation (cross-linking) techniques. Food Hydrocoll 101:105506. https://doi.org/10.1016/j.foodhyd.2019.105506 Tupa MV, Altuna L, Herrera ML, Foresti ML (2020) Preparation and Characterization of Modified Starches Obtained in Acetic Anhydride/Tartaric Acid Medium. Starch/Staerke 72:1–11. https://doi.org/10.1002/star.201900300 Golachowski A, Drożdz W, Golachowska M, et al (2020) Production and properties of starch citrates—Current research. Foods 9:1–14. https://doi.org/10.3390/foods9091311 Souza Almeida F, Guedes Silva KC, Matias Navarrete de Toledo A, Kawazoe Sato AC (2021) Modulating porosity and mechanical properties of pectin hydrogels by starch addition. J Food Sci Technol 58:302–310. https://doi.org/10.1007/s13197-020-04543-x Maaloul N, Oulego P, Rendueles M, et al (2021) Selected case studies on the environment of the mediterranean and surrounding Enhanced Cu ( II ) adsorption using sodium trimetaphosphate – modified cellulose beads : equilibrium , kinetics , adsorption mechanisms , and reusability. Environ Sci Pollut 46523–46539 Kabiri K, Zohuriaan-Mehr MJ (2004) Porous superabsorbent hydrogel composites: Synthesis, morphology and swelling rate. Macromol Mater Eng 289:653–661. https://doi.org/10.1002/mame.200400010 Sujka M, Sokolowska Z, Hajnos M, Wlodarczyk-Stasiak M (2016) Characterization of pore structure of rice grits extrudates using mercury intrusion porosimetry, nitrogen adsorption and water vapour desorption methods. J Food Eng 190:147–153. https://doi.org/10.1016/j.jfoodeng.2016.06.023 Da Silva Miranda Sechi N, Marques PT (2017) Preparation and physicochemical, structural and morphological characterization of phosphorylated starch. Mater Res 20:174–180. https://doi.org/10.1590/1980-5373-MR-2016-1008 Farhat W, Venditti R, Mignard N, et al (2017) Polysaccharides and lignin based hydrogels with potential pharmaceutical use as a drug delivery system produced by a reactive extrusion process. Int J Biol Macromol 104:564–575. https://doi.org/10.1016/j.ijbiomac.2017.06.037 Mantovan J, Giraldo GAG, Marim BM, et al (2021) Cellulose-based materials from orange bagasse employing environmentally friendly approaches. Biomass Convers Biorefinery. https://doi.org/10.1007/s13399-021-01279-2 Pozo C, Rodríguez-Llamazares S, Bouza R, et al (2018) Study of the structural order of native starch granules using combined FTIR and XRD analysis. J Polym Res 25:. https://doi.org/10.1007/s10965-018-1651-y Mantovan J, Giraldo GAG, Marim BM, et al (2023) Cellulose-based materials from orange bagasse employing environmentally friendly approaches. Biomass Convers Biorefinery 13:1633–1644. https://doi.org/10.1007/s13399-021-01279-2 Lu H, Liu Y, Yang Y, Li L (2017) Preparation of poly (vinyl alcohol)/gelatin composites via in-situ thermal/mechanochemical degradation of collagen fibers during melt extrusion: effect of extrusion temperature. J Polym Res 24:203. https://doi.org/10.1007/s10965-017-1377-2 Alharbi K, Ghoneim A, Ebid A, et al (2018) Controlled release of phosphorous fertilizer bound to carboxymethyl starch-g-polyacrylamide and maintaining a hydration level for the plant. Int J Biol Macromol 116:224–231. https://doi.org/10.1016/j.ijbiomac.2018.04.182 Müller CMO, Laurindo JB, Yamashita F (2009) Effect of cellulose fibers addition on the mechanical properties and water vapor barrier of starch-based films. Food Hydrocoll 23:1328–1333. https://doi.org/10.1016/j.foodhyd.2008.09.002 Kohler R, Alex R, Brielmann R, Ausperger B (2006) A new kinetic model for water sorption isotherms of cellulosic materials. Macromol Symp 244:89–96. https://doi.org/10.1002/masy.200651208 Additional Declarations No competing interests reported. Supplementary Files Graphicalabstract.tif Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. 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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-3755080","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":259906799,"identity":"13c5b052-445a-48db-b7da-df2963c8e762","order_by":0,"name":"BEATRIZ MARIM","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABD0lEQVRIiWNgGAWjYBACAyQyAcTg4QczC/BqYWxA1iIj2QBiGhDSggRsDA4g7MUKzNmbnz+uKKiL5p994CGQYcNjfH514ocHBgzy/GIHsGqx7Dlm2HjGgC13xrmEZMMzBmk8ZjfebpYAOsxw5uwE7A67kWDY2GDAk9twhiFNssHgMFDL2Q0gLQkGt3Fouf/8I1CLRO58iJb/PMYzzm7+gVfLDR6QLQa5GyBaDvAY8Pduw2uLZU9O4cwGg4TcjWcYkg0bDJJ5JG7wbrNIMJDA6Rdz9uMbPjb8qcudd4Yn8WHDHzt7/v6zm2/+qLCR55fGrgUJ8EBVSIBpCULKQYD9AITmP0CM6lEwCkbBKBhBAAB8u2GwnbtmxAAAAABJRU5ErkJggg==","orcid":"","institution":"State university of Londrina, Brazil","correspondingAuthor":true,"prefix":"","firstName":"BEATRIZ","middleName":"","lastName":"MARIM","suffix":""},{"id":259906800,"identity":"b2f23329-52a5-4215-b4ce-977dc56be736","order_by":1,"name":"Jessica Pereira","email":"","orcid":"","institution":"State university of Londrina, Brazil","correspondingAuthor":false,"prefix":"","firstName":"Jessica","middleName":"","lastName":"Pereira","suffix":""},{"id":259906801,"identity":"9da14b36-844c-4d90-a3a1-bfbfab25f420","order_by":2,"name":"Avacir Andrello","email":"","orcid":"","institution":"State university of Londrina, Brazil","correspondingAuthor":false,"prefix":"","firstName":"Avacir","middleName":"","lastName":"Andrello","suffix":""},{"id":259906803,"identity":"c937ac6d-cb5d-440f-8229-f14361b3304c","order_by":3,"name":"Suzana Mali","email":"","orcid":"","institution":"State university of Londrina, Brazil","correspondingAuthor":false,"prefix":"","firstName":"Suzana","middleName":"","lastName":"Mali","suffix":""}],"badges":[],"createdAt":"2023-12-14 18:59:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3755080/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3755080/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":48484251,"identity":"32315c29-c083-4a86-a323-85ccea6d8308","added_by":"auto","created_at":"2023-12-19 19:20:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1257343,"visible":true,"origin":"","legend":"\u003cp\u003eMicrotomographs 3D of samples\u003c/p\u003e\n\u003cp\u003ea - S-C-G (hydrogel formulated with native starch, cellulose and gelatin); b - S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/db1d9de8a84f4bc7479d46dc.png"},{"id":48484249,"identity":"630869a0-0069-44b0-8b58-fcd60b1b8aff","added_by":"auto","created_at":"2023-12-19 19:20:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":147840,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR spectra of samples.\u003c/p\u003e\n\u003cp\u003eS (native starch); MS(modified starch); C (cellulose); MC(modified cellulose); S-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin)\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/2d608edbae652fa1f10e8636.png"},{"id":48484250,"identity":"f67ca667-e05a-4b22-b51c-b9e9e17e3615","added_by":"auto","created_at":"2023-12-19 19:20:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":146715,"visible":true,"origin":"","legend":"\u003cp\u003eTGA/DTGA curves of hydrogels obtained by reactive extrusion.\u003c/p\u003e\n\u003cp\u003eS-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/9cf1d1f08364cc09f00fd84f.png"},{"id":48484252,"identity":"3d840e2a-a832-4ea2-8a5c-9b5987fb6df5","added_by":"auto","created_at":"2023-12-19 19:20:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":83995,"visible":true,"origin":"","legend":"\u003cp\u003eMoisture sorption isotherms curves of hydrogels obtained by reactive extrusion.\u003c/p\u003e\n\u003cp\u003eS-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/7b64b60ee928a6e3cf4c438d.png"},{"id":48484255,"identity":"84cabc8b-abea-4450-8edd-a4e9d483a69a","added_by":"auto","created_at":"2023-12-19 19:20:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":472823,"visible":true,"origin":"","legend":"\u003cp\u003eAppearance of hydrogels pellets after being immersed in water for 0, 24 and 48 h.\u003c/p\u003e\n\u003cp\u003eS-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin)\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/16304353f6110e19fdf59463.png"},{"id":48484788,"identity":"777cf622-4d01-4935-9e90-60d2dc269f12","added_by":"auto","created_at":"2023-12-19 19:28:33","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":65371,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of time and pH on swelling of hydrogels obtained by reactive extrusion.\u003c/p\u003e\n\u003cp\u003eS-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/1323fb41b71318b001456980.png"},{"id":53466098,"identity":"ff4a1e35-e7a7-4ee4-a5c9-752d0d3a1e30","added_by":"auto","created_at":"2024-03-26 10:25:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2506006,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/8dd0d594-73ce-4cd0-9cb2-cec8013fb764.pdf"},{"id":48484254,"identity":"9c7fae24-cc29-46e5-9a5b-5189fd7dfdab","added_by":"auto","created_at":"2023-12-19 19:20:34","extension":"tif","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":247640,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.tif","url":"https://assets-eu.researchsquare.com/files/rs-3755080/v1/a61790ab1008bd74bc8a8daa.tif"}],"financialInterests":"No competing interests reported.","formattedTitle":"Starch-cellulose-gelatin hydrogels obtained by reactive extrusion aiming an ecologically friendly perspective","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHydrogels have a three-dimensional structure with hydrophilic functional groups covalently bonded to the polymer main chain, endowing them with the capability to absorb water and swell, while maintaining structural integrity without dissolution. This stability in the presence of water is attributed to the intermolecular crosslinks within the three-dimensional polymeric network. In their desiccated state, hidrogels exhibit brittleness, but upon contact with water, they undergo a reversible transformation into an elastic gel, retaining their original configuration [\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThere are several applications for these materials, such as agriculture, pharmaceuticals, biomedical, hygiene products, effluent treatment and biosensors, and they are being widely applied in agriculture to increase the retention capacity of water and fertilizers in the soil, reducing the frequency of irrigation. In addition, these hydrogels have been used as seed coatings and root dips to aid germination and improve their habitability [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePolyacrylamide or polyacrylic acid are largely reported in literature as synthetic polymers that result in high performance hydrogels [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], however these polymers are non-biodegradable and obtained from non-renewable sources [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Recently, several hydrophilic biopolymers are being extensively studied for the production of hydrogels, and hydrogels consisting of a mixture of polymers are highlighted because there is greater interaction between chains of different structures, improving the characteristics of the material, thus the application of the hydrogel is expanded [\u003cspan additionalcitationids=\"CR15 CR16\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eStarch, gelatin and cellulose are considered interesting raw materials for the obtainment of hydrogels, these materials present numerous possibilities of chemical and physical modifications described in the literature, and also had several advantages, including its non-toxicity, biodegradability, biocompatibility, low cost, and wide availability. Additionally, they are listed as generally recognized as safe (GRAS) and included in the Food and Drug Administration Inactive Ingredient Guide [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. According to Gopinath et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], chemically modified cellulose and starch derivatives have been emerged as potential raw materials for obtainment of new hydrogels formulations.\u003c/p\u003e \u003cp\u003eGenerally, the most employed crosslinking agents for biopolymeric hydrogels based on starch, cellulose and gelatin are epichlorohydrin and glutaraldehyde, however they are toxic compounds and are not environmentally friendly [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Recently, an increased interest was observed in the use of low toxicity crosslinking agents such as citric acid (CA) or sodium trimetaphosphate (STMP) to obtain new hydrogels formulations, especially for natural polymer-based hydrogels [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eReactive extrusion can be used for biopolymers modification and also for hydrogels production and recent research reports the effectiveness of this technology. Cagnin et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] reported the production of hydrogels based on carboxymetilcellulose and starch by reactive extrusion using STMP as a crosslink agent. Sim\u0026otilde;es et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] reported the use of reactive extrusion for the obtainment of hydrogels based on starch and xanthan gum using CA as a crosslinker.\u003c/p\u003e \u003cp\u003eThis study aimed the production and characterization of biodegradable hydrogels using a mixture of starch, cellulose and gelatin as a polymeric matrix to be used as a potential water reservoir on agricultural systems by using an ecologically friendly perspective. Before being incorporated to the hydrogels formulations, cassava starch and cellulose were modified by reactive extrusion though reaction with CA and STMP, respectively, which were employed as green crosslinking agents. Subsequently, the hydrogels were produced by reactive extrusion as porous pellets, and they were characterized according to their porosity, thermal properties, degree of swelling at different times and pHs, and water adsorption capacities.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eThe hydrogel formulations were prepared with: 1) cassava starch (20% amylose and 80% amylopectin) purchased from Pinduca Co. Ltd. (Araruna, Brazil); 2) cellulose extracted from oat hulls using peracetic acid as a bleaching agent by the methodology described by Marim et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]; and 3) gelatin (Biotec, S\u0026atilde;o Paulo, Brazil). Glycerol (Synth) were employed as plasticizer and, citric acid (Synthlab, Diadema, Brazil) and sodium trimetaphosphate (Sigma Aldrich, St. Louis, USA) were employed to obtain modified starch and cellulose, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eMethods\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003eModification of cellulose and starch by reactive extrusion\u003c/h2\u003e \u003cp\u003eCA (20% - g acid/100 g starch) and STMP (0.1% - g STMP/100 g cellulose) were employed to obtain the modified cassava starch and cellulose from oat hull, respectively, based on method described by Gil-Giraldo et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The samples were prepared by dissolving different proportions of CA or STMP in distilled water, and the obtained solutions were mixed with starch and cellulose, respectively, resulting in samples with a final moisture content of 32% (g/g), which remained in sealed plastic bags at room temperature for 1h before extrusion. Starch and cellulose were extruded separately in a single screw extruder (AX Plastics, Diadema, Brazil) with a screw diameter of 1.6 cm and a screw length/screw diameter ratio (L / D) of 40, with four zones of heating and a matrix of 0.8 cm in diameter. The temperature in all zones was 100\u0026deg;C and the screw speed was 60 rpm. The starch and cellulose extrudates were collected, placed in an oven, dried to constant weight at 45\u0026deg;C, ground, and sieved in an 80-mesh sieve. Samples were washed three times with absolute ethanol to remove unreacted CA or STMP. Finally, the washed samples were air-dried at 45\u0026deg;C.\u003c/p\u003e \u003cp\u003eDegree of substitution (DS) of modified starch was calculated according to Volkert et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] by titration. For modified cellulose, the phosphorus content (%) was analyzed in triplicate by colorimetry in 600 nm (spectrophotometer Varian - Cary 50 Conc, S\u0026atilde;o Paulo, Brazil) and DS was calculated as follows [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]: DS\u0026thinsp;=\u0026thinsp;162*P/ (3100\u0026thinsp;\u0026minus;\u0026thinsp;102*P), where: P is phosphorus content (%); 162 is the molecular weight of the monomeric unit of cellulose, 3100 is the atomic weight of phosphorus multiplied by 100; and 102 is the group phosphate weight.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eHydrogels production\u003c/h2\u003e \u003cp\u003eFour formulations (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) were employed to obtain the biopolymeric hydrogels by reactive extrusion using different proportions of native and modified starch, cellulose and modified cellulose, and these proportions were determined by preliminary tests (data not presented), the formulations that were used were those that resulted in intact and easily processable pellets during the extrusion process. Gelatin and glycerol concentrations were fixed.\u003c/p\u003e \u003cp\u003eThe formulations were prepared by manually mixing the components with 35% glycerol, used as a plasticizer. The final mixtures were processed in a laboratory single-screw extruder (model EL-25, BGM, S\u0026atilde;o Paulo, Brazil) with a screw diameter (D) of 25 mm and a with a screw diameter (D) of 25 mm, a screw length of 26D, using a die with six 2 mm diameter holes. Barrel temperature profile was 90/120/130/115⁰ C, from the feed zone to the die zone, and a screw speed of 35 rpm was employed. Subsequently, the samples were pelleted dried in a circulation oven at 60\u0026deg; C for 3 h and used for characterization.\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\u003eFormulations used in the preparation of 100 g of hydrogels by reactive extrusion\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eComponents (g/100 g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eFormulations\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eS-C-G\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eS-MC-G\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eS.MS-C-G\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eS.MS-MC-G\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNative starch (S)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e51.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e51.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModified starch (MS)\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-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUnmodified cellulose (C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModified cellulose (MC)\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\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGelatin (G)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlycerol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e35.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003eMicrotomography and Porosity\u003c/h2\u003e \u003cp\u003eAn X-ray computed tomography (X-ray CT) was performed in a SkyScan-Bruker equipment (model 1172 MCT, Kontich, Belgium) to determine the porosity and pore size of the different hydrogel samples, in addition to presenting the image of the distribution of pores in each sample, performed in 3D. These tests were performed in triplicate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003eFourier Transform-Infrared Spectroscopy (FT-IR)\u003c/h2\u003e \u003cp\u003eApproximately 1 mg of each sample were pulverized, dried and mixed with potassium bromide (KBr) and compressed into tablets in a mass ratio of approximately 1:100 (sample to KBr). FT-IR spectroscopy for the samples was performed with a Shimadzu FT-IR -8300 spectrometer (Kyoto, Japan), the scanning range was 4000 to 500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with spectral resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eThermal properties\u003c/h2\u003e \u003cp\u003eThermogravimetric Analysis (TGA) of the samples were be performed using the Shimadzu TGA-50 (Japan) equipment. The scans were be performed at room temperature up to 600\u0026deg;C with a heating rate of 20\u0026deg;C/min under a nitrogen flow of 20 mL/min.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003eWater adsorption isotherms\u003c/h2\u003e \u003cp\u003eThe samples (0.5 g) were dried for 7 days in a desiccator containing anhydrous calcium chloride, and then they were placed at 25\u0026deg;C for 7 days in desiccators containing different saturated salt solutions providing specific water activities (aw) for the samples (0.11, 0.33, 0.43, 0.60, 0.75, and 0.90). Samples were dried at 105\u0026deg;C in a ventilated oven (035 Marconi MA, Piracicaba, Brazil) to determine their equilibrium moisture content at each aw condition. The GAB model (Guggenheim\u0026ndash; Anderson-de Boer) was used to fit the sorption isotherm data, and the monolayer values were calculated from the GAB isothermal model [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] as follows: M = (m\u003csub\u003e0\u003c/sub\u003eCK\u003csub\u003eaw\u003c/sub\u003e) / (1\u0026thinsp;\u0026minus;\u0026thinsp;K\u003csub\u003eaw\u003c/sub\u003e) (1\u0026thinsp;\u0026minus;\u0026thinsp;K\u003csub\u003eaw\u003c/sub\u003e + CK\u003csub\u003eaw\u003c/sub\u003e), where M is the equilibrium moisture (g water / 100 g solids), aw is the water activity, m\u003csub\u003e0\u003c/sub\u003e is the monolayer value (g water / 100 g solids), and C and K are GAB constants.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eDegree of swelling at different times and different pHs\u003c/h2\u003e \u003cp\u003eDegree of swelling was determined by gravimetric method using previously weighed cylindrical devices (3.0 x 3.5 cm) containing at one end a screen with a nominal opening of 138 x 75 mm, as described by Pereira, Lonni and Mali [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. About 1g of each sample was weighed and placed inside the devices and then immersed in 10 mL of a different pH solution (4.0, 7.0 and 9.0) at 25\u0026deg;C. At predetermined times (30min, 24h and 48h), the devices containing the hydrogel pellets were removed from the solutions, the excess was removed with filter paper and then weighed. From the value obtained, the degree of swelling (g/g) of each sample was calculated in relation to its initial dry weight. Analyzes were performed in triplicate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAnalyses of variance (ANOVA) and Tukey's mean comparison test (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) were performed with Statistica software version 7.0 (Statsoft, OK, USA).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eModification of starch and cellulose\u003c/h2\u003e \u003cp\u003eCassava starch was modified by reactive extrusion, and degree of substitution (DS) was 0.365 for CA-modified starch. Citric acid (C₆H₈O₇) is a tricarboxylic acid that acts as an esterifying agent for starch, but also as crosslinker agent, which results in increased stability of biopolymeric matrix [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Ye et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] modified rice starch by reactive extrusion with CA and observed DS between 0.037 and 0.138 when the CA levels ranged from 10 to 40% (g CA/100 g starch).\u003c/p\u003e \u003cp\u003eRegarding to the STMP-modified cellulose sample, the DS was 0.01. DS can be consider a good indicative of the occurrence of crosslinking of the phosphate groups grafted onto the polysaccharides chain [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The value observed in this study was lower when compared to DS reported by Cagnin et al.[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], who reported DS values of 0.05 for hydrogels obtained by reactive extrusion from cassava starch and carboxymethylcellulose crosslinked with STMP (4 g/100 g).\u003c/p\u003e \u003cp\u003eCrosslinking agents as CA and STMP are capable of forming ester intermolecular linkages between specific groups on starch and cellulose molecules, and depending on the level of substitution, the polymer network is reinforced and results in changes in solubility and degree of swelling power [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], and according to Golachowski et al. [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], these changes are directly correlated with the degree of substitution.\u003c/p\u003e \u003cp\u003eAdditionally, CA and STMP were employed in this study because they are considered low toxicity crosslinking agents [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] in comparison to epichlorohydrin and glutaraldehyde, which are toxic compounds and are not environmentally friendly [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], and conventionally employed as crosslinking agents in starch, cellulose and gelatin hydrogels.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eMicrotomography and Porosity\u003c/h2\u003e \u003cp\u003eThe S-C-G sample showed the lowest porosity compared to the other samples (34.99%, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), whereas the S.MS-MC-G sample prepared with modified starch and modified cellulose showed the highest porosity values (47.34%, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and a significant quantity of open pores (342.11%). Possibly, the modification of starch and cellulose resulted in a more expandable polymer matrix due to the introduction of new bonds between the polymeric chains. This led to a more stable melt that expanded upon exiting thef the extruder, mainting the porous structure of the material. As observed by Almeida et al. [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] the addition of starch to pectin hydrogels can enhance the three-dimensional network of the hydrogel, increasing the quantity of closed pores and resulting in a more compact and cohesive network.\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\u003ePorosity, open pores, and closed pores of 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\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePorosity (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOpen Pores (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eClosed Pores (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-C-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e34.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.28b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-MC-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14a,b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36.42\u0026thinsp;\u0026plusmn;\u0026thinsp;1.52b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a,b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.MS-C-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30.49\u0026thinsp;\u0026plusmn;\u0026thinsp;1.09b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.25\u0026thinsp;\u0026plusmn;\u0026thinsp;1.99b,c\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.MS-MC-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e47.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42.11\u0026thinsp;\u0026plusmn;\u0026thinsp;1.19a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.53\u0026thinsp;\u0026plusmn;\u0026thinsp;1.05c\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\u003eS-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin). Data are the means of replicate determinations\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. Different letters in the same column indicate significant differences (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) between means (Tukey test).\u003c/p\u003e \u003cp\u003eDuring reactive extrusion, high temperatures induce rapid evaporation leading to the formation of pores as water leaves the molten material. Evaporation is influenced by the material\u0026acute;s resistance to the pressure exerted by water vapor, along with extrusion process variables such as temperature and screw speed [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. While these variables typically increase hydrogel porosity, in this study, the same conditions were standardized for all samples, attributing differences in results to formulation components. Cagnin et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] reported lower porosity values (below 11%) for carboxymethylcellulose and starch hydrogels obtained by reactive extrusion using STMP as a crosslinking agent, highlighting the influence of raw materials and processing conditions.\u003c/p\u003e \u003cp\u003ePorous material produced by extrusion typically displays irregular pore size [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The microtomography presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows images of the S-C-G and S.MS-MC-G samples with the lowest and highest porosity values (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). It is observed that in the S-C-G sample, the pores are small and uniformly distributed throughout the pellet, while in the S.MS-MC-G sample, there is a greater quantity of pores and open pores. The addition of modified starch and modified cellulose may have accelerated water evaporation from the material, leading to the formation of open pores in the pellets. Maaloul et al. [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] demonstrated that the addition of STMP resulted in hydrogels with open pores and interconnected irregular cavities, causing a higher quantity of open pores compared to the other samples.\u003c/p\u003e \u003cp\u003ePorous hydrogels enhance water absorption through capillary forces, with open pores providing the hydrogel the ability to absorb water rapidly, regardless of size in the dry state. These open pores establish communication channels with the external environment, improving the expansion properties of the hydrogel [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. On the other hand, hydrogels with a higher quantity of closed pores are relevant for mechanical strength and elasticity, applicable in situations requiring high mechanical resistance properties, such as in agricultural applications when the hydrogel is applied in deep soil and needs to withstand associated pressures. These hydrogels can also be employed in situations where water absorption rate is not a primary concern [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eFourier Transform-Infrared Spectroscopy (FT-IR)\u003c/h2\u003e \u003cp\u003eAs seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, a new important band at 1730 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e appeared in modified starch (MS) sample, it was attributed to the stretching vibration of the carbonyl ester group, indicating that the ester bonds were formed successfully. These results agreed with those presented by other authors [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan additionalcitationids=\"CR39\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], who used CA as esterifying and crosslinking agent for starch modification.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFT-IR spectra of hydrogel samples are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. It was possible to identify an important band at 1730 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, in the samples that were prepared with modified starch (S.MS-C-G and S.MS-MC-G), attributed to the stretching vibration of the carbonyl ester group, which provides evidence of ester bonds formed in the CA-modified starch used to prepare the hydrogels\u003c/p\u003e \u003cp\u003eOther bands are observed in the FT-IR spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) of all hydrogels samples: a broad band at 3400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e attributed to stretching of OH stretching in hydrogen bonds; a band at 2900 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e that was associated CH group stretching vibration (CH\u003csub\u003e2\u003c/sub\u003e groups) [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The characteristic e bands of cellulose were also distinguished at 1017 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026ndash;O\u0026ndash;C pyranose ring vibration) and 895 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (β-glycosidic bond bending) [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSpecific bands of the phosphate groups at 1214 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (P\u0026thinsp;=\u0026thinsp;O elongation), 1129 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (symmetric and asymmetric stretching of the PO\u003csub\u003e2\u003c/sub\u003e group), and 889 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (PO bond) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) appeared in all hydrogels samples without any difference in intensity or shift, including the sample prepared with STMP-modified cellulose (S.MS-MC-G). This occurred probably due to the low concentration of STMP used, and additionally these bands may be covered by other bands between 1200 and 800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is characteristic of starch and cellulose [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Some authors reported that they did not detect these phosphate bands in crosslinked STMP starch and cellulose, and they attributed this to the low concentration of phosphate groups [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eKhan et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] reported that pure gelatin presents characteristics bands at 3430 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e due to amide \u0026ndash;N\u0026ndash;H elongation and at 1670 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e due to amine groups. It can be seen that in all hydrogels samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) da band at 1650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which can be an indicative of the formation of hydrogen bonds between OH groups of starch and cellulose with amine groups of gelatin [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Lu et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] also reported that free carboxylic groups of gelatin can be esterified with hydroxyl groups of other polymers, such as cellulose and starch.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eThermal properties\u003c/h2\u003e \u003cp\u003eTGA and DTGA curves are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e. For all hydrogel samples, the main weight loss occurred between 320 to 330\u0026deg;C, (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e), which can be associated with the degradation of starch and cellulose [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], and other peaks were observed at 160\u0026deg;C. These results are interesting results, indicating that the obtained hydrogels can support up to a temperature of 300\u0026deg;C without being significantly degraded. Rodr\u0026iacute;guez-Castellanos et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] produced starch - gelatin hydrogels reinforced with cellulose by reactive extrusion, and they described that the weight loss observed at 160\u0026ndash;170\u0026deg;C may be associated with the glycerol content in the polymer matrix, while the peaks at 266\u0026deg;C were associated to the degradation of long chains of gelatin. The peaks observed at 490\u0026deg;C indicate denaturation of the gelatin.\u003c/p\u003e\u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eMoisture sorption isotherms\u003c/h2\u003e \u003cp\u003eThe moisture sorption isotherms and parameters of the GAB model are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, respectively. All samples had a similar shape characteristic of hydrophilic materials and most starch and cellulose based materials [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] which means that hydrogels produced by reactive extrusion have a high affinity for water when exposed to high activity of water (a\u003csub\u003ew\u003c/sub\u003e). The GAB model was efficient to describe the moisture sorption isotherms of the hydrogel samples (R2\u0026thinsp;=\u0026thinsp;0.99).\u003c/p\u003e \u003cp\u003eThe sorption isotherms of all samples showed similar patterns, with an increase in water activity (aw) when there was observed an increase in equilibrium moisture contents. The monolayer value (m\u003csub\u003e0\u003c/sub\u003e) indicates the maximum amount of water adsorbed in a single layer per gram of dry material that can be related to the sorption sites [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. According to the parameters presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the sample produced with native starch and unmodified cellulose had the highest m\u003csub\u003e0\u003c/sub\u003e (53.25/100g) while samples prepared with modified starch had the lowest values (S.MS-C-G and S.MS-MC-G). These results indicate that the addition of modified starch in the samples decreased their capacity of adsorb water when stored in environments with higher relative humidities. Possibly, starch modification with CA resulted in a reinforced polymeric matrix, when free hydroxyl groups of starch were esterified, which resulted in a lower ability to interact with water.\u003c/p\u003e \u003cp\u003eThe parameter k is related to the heat of sorption of the multilayer region and, generally, the values of this parameter are less than 1, and the values of k ranged from 0.46 (S-C/G) and 3.59 (S.MS-C-G), respectively (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The parameter C is related to the sorption heat of the first layer, 0.58 to 0.88 (S.MS-C-/G and S.MS-MC-G).\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\u003eGAB model parameters of hydrogels\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003em0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eK\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-C-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e53.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-MC-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.MS-C-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.MS-MC-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.99\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\u003eS-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin). GAB model: M = (m\u003csub\u003e0\u003c/sub\u003eCKaw)/(1\u0026thinsp;\u0026minus;\u0026thinsp;Ka\u003csub\u003ew\u003c/sub\u003e) (1\u0026thinsp;\u0026minus;\u0026thinsp;Ka\u003csub\u003ew\u003c/sub\u003e + CKa\u003csub\u003ew\u003c/sub\u003e), where M is the equilibrium moisture (g water/100 g solids), a\u003csub\u003ew\u003c/sub\u003e is the water activity, m\u003csub\u003e0\u003c/sub\u003e is the monolayer value (g water/100 g solids), and C and K are GAB constants\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eDegree of swelling at different times and pHs\u003c/h2\u003e \u003cp\u003eThe effects of time and pH on the degree of swelling of hydrogels obtained by reactive extrusion can be seen in Figs.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003e and the effect of pH after 48 h of contact with water can be seen on Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eA first visual analysis was performed to determine how long the granules could be immersed in distilled water without losing their structure. This criterion was established with a focus on the possible future application of hydrogel pellets, for which structural integrity is critical. However, all samples could remain submerged in water for more than 48h without dissolving or lose their shape. In Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e5\u003c/span\u003e it was possible to observe the intact and swollen pellets after 48 immersed in water.\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003e it can be observed that the swelling of hydrogels pellet increased rapidly after 30 min of contact with water, but after 24 h the swelling degree stabilizes. Chemical and physical forces induce the liquid in a polymeric matrix, being responsible for the swelling of hydrogels. In the beginning there is rapid sorption of water, as there is a lot of free space between the chains, then the absorption rate decreases, as the molecules cannot bind at the crosslinking points, which act as barriers, bringing the material to equilibrium. The time required for the hydrogel to equilibrate depends on the crosslink density, extent of porosity and chemical composition, which determine characteristics such as hydrophilicity, charge and intermolecular interactions [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan additionalcitationids=\"CR46\" citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e it was observed that there was no significant difference between the degree of swelling of the different hydrogels samples at pH 7 after 48 h immersed in water, except for sample S.MS-MC-G that presented the higher significantly value (6.07 g/g). This sample, which was formulated with both CA-modified starch and STMP-modified cellulose, also presented the highest values of porosity and open pores, which favored water absorption in this sample. Modification of starch and cellulose resulted in the introduction of new linkages between polymeric chains. When samples were subjected to pH 4 and pH 9, small variations were observed in the different formulations, however it was difficult to related these variation to hydrogels formulations.\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\u003eDegree of swelling of hydrogel samples for 48 h at different pH values\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\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eDegree of Swelling (g/g)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003epH 4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003epH 7\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003epH9\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-C-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003csup\u003eaA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003csup\u003ebA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003csup\u003eabB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-MC-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003csup\u003ebaA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003csup\u003ebA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003csup\u003ebB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.MS-C-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003csup\u003ebB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59\u003csup\u003ebA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003csup\u003eabB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.MS-MC-G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003csup\u003ebB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003csup\u003eaA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.53\u003csup\u003ebB\u003c/sup\u003e\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\u003eS-C-G (hydrogel formulated with native starch, cellulose and gelatin); S-MC-G (hydrogel formulated with native starch, modified cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, cellulose, and gelatin); S.MS-C-G (hydrogel formulated with native starch, modified starch, modified cellulose, and gelatin). Data are the means of replicate determinations\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. Different small letters in the same column indicate significant differences (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) between means, and different capital letters in the same line indicate significant differences (p\u0026thinsp;\u0026le;\u0026thinsp;0.05) between means (Tukey test).\u003c/p\u003e \u003cp\u003eComparing the effect of pH on degree of swelling of hydrogels samples, it can be observed that the highest values were observed for all samples at pH 7, with values ranging from 5.37 to 6.07 g/g (537\u0026ndash;607% of swelling), however in pH 9 degree of swelling decreased for all samples (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). According to Khan et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], when the water absorption content can exceed more than 95 percent of the total weight or volume of the hydrogel, these hydrogels can be referred to as superabsorbent hydrogels, thus, the hydrogels obtained in this study can be considered as superabsorbent hydrogels, which in the most important property in a material that will be used for water retention on agricultural systems.\u003c/p\u003e \u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eReactive extrusion process was efficient to produce hydrogels based on citric acid-modified starch, STMP-modified cellulose and gelatin. After 48 h soaked in pH 7, they obtained higher values of degree of swelling (up to 530%), and the hydrogel sample formulated with both CA-modified starch and STMP-modified cellulose presented the highest values of porosity (\u0026gt;\u0026thinsp;45%) and open pores (\u0026gt;\u0026thinsp;5%), and the higher degree of swelling (607%), which makes these materials potential candidates for application as water retainers on agricultural systems, with important advantages, including their biodegradability, low toxicity and low environmental impact resulting from their production process. Additionally, it is worth mentioning that the reactive extrusion process used is a continuous process, with low effluent generation and scalable for large-scale production.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMarim B.M. and Mali S. authored the main text of the manuscript, while Andrello prepared Figure 1 and Table 2. Pereira J.F. assisted in all experiments and contributed to writing portions of the main text, particularly focusing on thermal properties. All authors reviewed the manuscript.\u003c/p\u003e\nCompeting Interests: There are no competing interests to declare."},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eDamiri F, Salave S, Vitore J, et al (2023) Properties and valuable applications of superabsorbent polymers: a comprehensive review. Springer Berlin Heidelberg\u003c/li\u003e\n\u003cli\u003eDas D, Bhattacharjee S, Bhaladhare S (2023) Preparation of Cellulose Hydrogels and Hydrogel Nanocomposites Reinforced by Crystalline Cellulose Nanofibers (CNFs) as a Water Reservoir for Agriculture Use. ACS Appl Polym Mater 5:2895\u0026ndash;2904. https://doi.org/10.1021/acsapm.3c00109\u003c/li\u003e\n\u003cli\u003eKaur P, Bohidar HB, Nisbet DR, et al (2023) Waste to high-value products: The performance and potential of carboxymethylcellulose hydrogels via the circular economy. Cellulose 30:2713\u0026ndash;2730. https://doi.org/10.1007/s10570-023-05068-0\u003c/li\u003e\n\u003cli\u003eKadry G, El-Gawad HA (2023) Rice straw derived cellulose-based hydrogels synthesis and applications as water reservoir system. Int J Biol Macromol 253:127058. https://doi.org/10.1016/j.ijbiomac.2023.127058\u003c/li\u003e\n\u003cli\u003eKhan BA, Ullah S, Khan MK, et al (2020) Fabrication, Physical Characterizations, and In Vitro, In Vivo Evaluation of Ginger Extract-Loaded Gelatin/Poly(Vinyl Alcohol) Hydrogel Films Against Burn Wound Healing in Animal Model. AAPS PharmSciTech 21:1\u0026ndash;10. https://doi.org/10.1208/s12249-020-01866-y\u003c/li\u003e\n\u003cli\u003eSim\u0026otilde;es BM, Cagnin C, Yamashita F, et al (2020) Citric acid as crosslinking agent in starch/xanthan gum hydrogels produced by extrusion and thermopressing. 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Macromol Symp 244:89\u0026ndash;96. https://doi.org/10.1002/masy.200651208\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"Biopolymers, Porosity, Swelling, Microstructure","lastPublishedDoi":"10.21203/rs.3.rs-3755080/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3755080/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBiopolymeric hydrogels represent a versatile class of materials with a wide range of potential applications, including their use in agricultural materials, drug delivery systems, biosensors, and food packaging. This investigation primarily centered on the synthesis and characterization of biodegradable hydrogels based on starch, cellulose, and gelatin, acting as a polymeric matrix intended for water retention in agricultural contexts. Prior to their incorporation into the hydrogels formulations, cassava starch and cellulose extracted from oat hulls underwent modification via reactive extrusion involving reaction with citric acid (CA) and sodium trimetaphosfate (STMP) as crosslinking agents, respectively. The hydrogels were obtained through a reactive extrusion process to produce porous pellets. These pellets were characterized according to their porosity, thermal properties, degree of swelling at different times and pHs, and water adsorption capacities. The hydrogel sample formulated with both CA-modified starch and STMP-modified cellulose, and gelatin, presented the highest values of porosity (\u0026gt;\u0026thinsp;45%) and open pores (\u0026gt;\u0026thinsp;5%), and the higher degree of swelling (607%). These materials as promising candidates for application in agriculture to increase water and/or fertilizers retention capacity in soil, with important advantages, including their biodegradability and low toxicity. It is worth mentioning that the reactive extrusion process used is a continuous process, with low effluent generation and scalable for large-scale production.\u003c/p\u003e","manuscriptTitle":"Starch-cellulose-gelatin hydrogels obtained by reactive extrusion aiming an ecologically friendly perspective","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-12-19 19:20:29","doi":"10.21203/rs.3.rs-3755080/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":"ea054324-36b6-4aca-bbd7-7df86d877363","owner":[],"postedDate":"December 19th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-26T10:16:54+00:00","versionOfRecord":[],"versionCreatedAt":"2023-12-19 19:20:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3755080","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3755080","identity":"rs-3755080","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}