Thermal and dielectric properties of powder coatings based on carboxylated polyester and β-hydroxyalkylamide

Thermal transitions, relaxations and the crosslinking reaction in varnishes and pigmented paints based on carboxylated polyester and β-hydroxyalkylamide (Primid) were studied by differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC), thermogravimetry (TGA) and dielectric analysis (DEA). The effect of the Primid content on the glass transition of the powder coatings before and after crosslinking was analysed. The melting and flow regions were studied by TMDSC and correlated with the loss factor, which was measured by DEA. A comparison of the DSC and TGA scans showed that the crosslinking reaction was masked by the vaporisation of water formed during esterification. The resulting endothermic reaction made it difficult to analyse the crosslinking by DSC. Nevertheless, it was possible to detect the crosslinking reaction by the dielectric measurement of the loss factor and the conductivity.     

Gelatin renaturation and viscosity of dilute gelatin solutions

Mechanical melting temperatures of gelatin gels determined by the ball-drop method are decreased by several degrees if 0.5m potassium thiocyanate aqueous solution is used as solvent instead of pure water. In agreement with that, the growth with time of the viscosity of dilute gelatin solutions occurs at lower temperatures in 0.5m potassium thiocyanate. Surprisingly enough, the reduced specific viscosity after five hours at 5° C is lower in pure water. This is because the temperature dependence of this quantity in water is not monotonic, and the temperature 5° C is below that at which a distinct maximum is reached. No similar maximum has been reported so far for the temperature and time dependences of the extent of renaturation determined by optical techniques. The difference between the results of these two methods could be ascribed to the fact that the viscosity of solutions of partially renaturated gelatin is given not only by the fraction of monomer units in the helical conformation but also by the average length of created helices.     

Thermal properties measurements of renatured gelatin using conventional and temperature modulated differential scanning calorimetry

The thermal properties of amorphous gelatin films and gelatin films with renatured structural order were measured by using conventional and temperature modulated differential scanning calorimetry (DSC). Different amounts of gelatin structural order associated with a melting enthalpic change in the DSC measurement were prepared based on different gelatin drying conditions. Two consecutive heating and cooling DSC measurements on the gelatin films showed that there was no change in the glass‐transition temperature (T_g) for the amorphous gelatin but there was a decrease in the T_g for the structural gelatin on the second DSC scan. This decrease was attributed to the plasticizing effect from the release of originally hydrogen‐bonded water associated with the structural gelatin. In addition, a reversing endotherm observed upon melting of the structural gelatin during a temperature modulated DSC measurement indicated that the transition of bound water to free water occurred as the partial triple‐helix gelatin melted. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1795–1801, 2006     

Microwave-assisted reaction of gelatin with tannic acid: non-thermal effect on the crosslinking process

The reaction of gelatin with tannic acid using microwave heating with simultaneous cooling (MHSC) in comparison with water bath heating was investigated to get some hints on the non-thermal effect of microwave. MHSC showed a better ability to accelerate the reaction rate. It also increased the turbidity, crosslinking degree, and viscosity of the crosslinked gelatin by 91 FTU, 6.8%, and 0.08 respectively, indicating that microwave could improve the properties of the product. Moreover, sodium dodecyl sulfate polyacrylamide gel electrophoresis patterns reflected that the crosslinked gelatin (MHSC) had a higher molecular weight as the gray levels decreased by 9.2% (235–245?kDa), 2.3% (135–145?kDa), and 9.3% (122–132?kDa). More homogeneous aggregations were identified at the crosslinked gelatin by atomic force microscopy. These results proved that microwave has a non-thermal effect in the gelatin crosslinking process, accelerating the crosslinking reaction, and improving the performance of the gelatin product, which may have a good use in industry.     

Flame retardancy and nondripping properties of ammonium polyphosphate/poly(butylene succinate) composites enhanced by water crosslinking

Ammonium polyphosphate (APP)/poly(butylene succinate) (PBS) composites were prepared with a unique water‐crosslinking technique to improve the flame retardancy and nondripping properties of the composites and to maintain the main structure of the composites during flame tests. The composites were treated with a coupling agent (tetraethoxysilane) and then were compounded in a twin‐screw extruder. The compound was moisture‐crosslinked. Fourier transform infrared spectra were used to monitor the water‐crosslinking reaction. The composites via the water‐crosslinking treatment exhibited improved mechanical properties because of the interfacial bonding between the APP and PBS matrix. Scanning electron microscopy of the fractured surfaces of the water‐crosslinked composites showed that the void size increased with increasing water‐crosslinking time. Composites with 15 wt % APP were classified as UL‐94 V‐2; however, the ones with only a 0.5‐h water‐crosslinking reaction were classified as UL‐94 V‐0. Thermal analyses of the water‐crosslinked composites indicated that the thermal degradation temperature of the composites increased with increasing water‐crosslinking time. Differential scanning calorimetry results revealed that the water‐crosslinking reaction could limit the crystallization rate of PBS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2935–2945, 2006     

Chitosan/gelatin porous bone scaffolds made by crosslinking treatment and freeze‐drying technology: Effects of crosslinking durations on the porous structure,compressive strength,and in vitro cytotoxicity

In this study, freezing was used to separate a solute (polymer) and solvent (deionized water). The polymer in the ice crystals was then crosslinked with solvents, and this diminished the linear pores to form a porous structure. Gelatin and chitosan were blended and frozen, after which crosslinking agents were added, and the whole was frozen again and then freeze‐dried to form chitosan/gelatin porous bone scaffolds. Stereomicroscopy, scanning electron microscopy, compressive strength testing, porosity testing, in vitro biocompatibility, and cytotoxicity were used to evaluate the properties of the bone scaffolds. The test results show that both crosslinking agents, glutaraldehyde (GA) and 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide, were able to form a porous structure. In addition, the compressive strength increased as a result of the increased crosslinking time. However, the porosity and cell viability were not correlated with the crosslinking times. The optimal porous and interconnected pore structure occurred when the bone scaffolds were crosslinked with GA for 20 min. It was proven that crosslinking the frozen polymers successfully resulted in a division of the linear pores, and this resulted in interconnected multiple pores and a compressively strong structure. The 48‐h cytotoxicity did not affect the cell viability. This study successfully produced chitosan/gelatin porous materials for biomaterials application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41851.     

Vitrification,devitrification, and dielectric relaxations during the non‐isothermal curing of diepoxy‐cycloaliphatic diamine

The curing of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) with a diamine based on 4,4′‐diamino‐3,3′‐dimethyldicyclohexylmethane (3DCM) was analyzed by dielectric relaxation spectroscopy (DRS) between ?100 and 220°C, at heating rates ranging from 0.1 to 2 K min^?1. The permittivity, ε′, and the loss factor, ε″, were measured by DRS in the frequency range between 1 and 100 kHz. The dielectric relaxations were correlated with the relaxations observed previously by temperature modulated differential scanning calorimetry (TMDSC) at the same heating rates and in modulation conditions of amplitude 0.2 K and a period of 60 s, which is equivalent to a measuring frequency of 16.7 mHz. The dielectric measurements showed three frequency‐dependent dipolar relaxations and one ionic relaxation, which was independent of the frequency. The dipolar relaxations were associated with the glass transition of the unreacted system and the vitrification and the devitrification processes of the system during the crosslinking reaction, and the ionic relaxation was associated with the beginning of the crosslinking reaction. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 558–563, 2006     

Synergistic effects of crosslinking and chitosan molecular weight on the microstructure,molecular mobility,thermal and sorption properties of porous chitosan/gelatin/hyaluronic acid scaffolds

In this study, synergistic effects of crosslinking and chitosan molecular weight on the microstructure, molecular mobility, thermal, and sorption properties of porous chitosan/gelatin/hyaluronic acid hybrid foams are reported. Fourier transform infrared spectroscopy has been utilized to confirm the covalent attachment of hyaluronic acid to gelatin and chitosan, and covalent chemical crosslinking between gelatin and chitosan. Detailed image analysis of scanning electron microscopy images of the porous scaffold hydrids reveal that the pore size of the materials formulated using either low‐ or high‐molecular‐weight chitosan increases significantly upon crosslinking using ethyl(dimethylaminopropyl) carbodiimide/N‐Hydroxysuccinimide. These microstructural changes are even more pronounced for the crosslinked hybrid scaffolds formulated using low‐molecular‐weight chitosan, highlighting a synergistic effect between crosslinking and the use of low‐molecular‐weight chitosan. Results obtained using differential scanning calorimetry demonstrate a significant reduction in molecular mobility reduction in molecular mobility for crosslinked scaffolds formed using high‐molecular‐weight chitosan compared to non‐crosslinked hybrids and crosslinked hybrids formulated using low‐molecular‐weight chitosan. Correspondingly, dynamic vapor sorption evidenced significantly lower water vapor sorption for crosslinked scaffolds formulated using high‐molecular‐weight chitosan. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44772.     

Depolymerization of nylon 6 waste fibers

The depolymerization of nylon 6 was carried out with various solvents, such as formic acid, hydrochloric acid, and sulfuric acid, followed by heating under reflux for different times. From the polymer dissolved and refluxed in formic acid, degradation products with different ranges of molecular weights were collected by fractional precipitation, with small lots of distilled water added as a nonsolvent. The characterization of different fractions was carried out by the measurement of the viscosity‐average molecular weight, the number‐average molecular weight, and the number of amino end groups. The presence of the monomer, aminocaproic acid, was confirmed by thin‐layer chromatography in the case of hydrochloric acid treated nylon 6. With a strongly acidic ion‐exchange resin, the monomer was separated in its purest form, and the melting point was noted. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 186–190, 2006     

Crosslinking structures of gelatin hydrogels crosslinked with genipin or a water‐soluble carbodiimide

It was suggested in our previous studies that carbodiimide‐ and genipin‐crosslinked gelatin hydrogels could be used as bioadhesives to overcome the cytotoxicity problem associated with formaldehyde‐crosslinked gelatin hydrogels. In this study, we investigated the crosslinking structures of carbodiimide‐ and genipin‐crosslinked gelatin hydrogels. We found that crosslinking gelatin hydrogels with carbodiimide or genipin could produce distinct crosslinking structures because of the differences in their crosslinking types. Carbodiimide could form intramolecular crosslinks within a gelatin molecule or short‐range intermolecular crosslinks between two adjacent gelatin molecules. On the basis of gel permeation chromatography, we found that the polymerization of genipin molecules could occur under the conditions used in crosslinking gelatin hydrogels via a possible aldol condensation. Therefore, besides intramolecular and short‐range intermolecular crosslinks, additional long‐range intermolecular crosslinks could be introduced into genipin‐crosslinked gelatin hydrogels. Crosslinking a gelatin hydrogel with carbodiimide was more rapid than crosslinking with genipin. Therefore, the gelation time for the carbodiimide‐crosslinked gelatin hydrogels was significantly shorter than that of the genipin‐crosslinked gelatin hydrogels. However, the cohesive (interconnected) structure of the carbodiimide‐crosslinked gelatin hydrogels was readily broken because, unlike the genipin‐crosslinked gelatin hydrogels, there were simply intramolecular and short‐range intermolecular crosslinks present in the carbodiimide‐crosslinked hydrogel. In the cytotoxicity study, the carbodiimide‐crosslinked gelatin hydrogels were dissolved into small fragments in the cultural medium within 10 min. In contrast, the genipin‐crosslinked gelatin hydrogels remained intact in the medium throughout the entire course of the study. Again, this may be attributed to the differences in their crosslinking structures. The genipin‐crosslinked gelatin hydrogels were less cytotoxic than the carbodiimide‐crosslinked gelatin hydrogels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4017–4026, 2004     

Effect of gamma irradiation on the interpenetrating networks of gelatin and polyacrylonitrile: Aspect of crosslinking using microhardness and crosslink density measurements

The present article reports the effect of gamma irradiation on the hardness behavior of the interpenetrating polymer networks (IPNs) of gelatin and polyacrylonitrile (PAN). Various compositions of gluteraldehyde‐crosslinked gelatin and N, N′‐methylene bis acrylamide (MBA)‐crosslinked PAN were prepared and investigated for microhardness studies. The pre‐ and post‐irradiated IPNs were characterized for their crosslinking density, determined with swelling ratio measurements. It was found that the crosslinked IPNs get further hardened because of radiational hardening at specific doses in the range from 2 to 250 kGy. The role of acrylonitrile and crosslinker (MBA) in the IPNs, as a consequence of irradiation, has also been explained. A fair consistency has been observed between the microhardness results and crosslinking density measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2581–2586, 2006     

Functional characteristics of gelatin extracted from skin and bone of Tiger-toothed croaker (Otolithes ruber) and Pink perch (Nemipterus japonicus)

The utilization of waste from fish processing industry for production of value added products has attracted substantial attention. Tiger-toothed croaker (Otolithes ruber) and Pink perch (Nemipterus japonicus) are used for surimi production and have the potential of abundant supply of raw skins and bones. In order to evaluate the waste from Tiger-toothed croaker and Pink perch as a source of gelatin, the gelatin was extracted from skin and bones and its rheological and functional properties were examined. The skins of Tiger-toothed croaker and Pink perch yielded 7.56% and 5.57% gelatin, whereas their bones yielded 4.57% and 3.55% respectively indicating skin as an important source for gelatin production. The gel strength of gelatins from the skins and bones of Tiger-toothed croaker (170 g and 140 g respectively) were found higher than Pink perch skin and bone gelatins (150 g and 130 g respectively). Similarly, the viscosity, melting point, emulsifying capacity and stability, foaming capacity and stability, and water holding capacity of gelatin extracted from Tiger-toothed croaker were in general greater than those of the gelatin from Pink perch and the values of skin gelatin were higher compared to bone gelatin in both the species. Hydroxyproline contents in skin and bone of Tiger-toothed croaker were 7.77 and 7.51 mg/g and in Pink perch they were 7.63 and 7.41 mg/g respectively. It can be concluded from the present study that Tiger-toothed croaker skin is a prospective source to produce gelatin in good yield with desirable functional properties comparable to commercially available mammalian gelatins.     

Performance evaluation of silane crosslinking of metallocene‐based polyethylene–octene elastomer

Vinyl trimethoxysilane (VTMS) was grafted onto metallocene‐based polyethylene–octene elastomer (POE) using a free‐radical reaction of VTMS and dicumyl peroxide as an initiator, and then the grafted POE was crosslinked in the presence of water. The effects of VTMS concentration on crystallization behavior, mechanical properties, and thermal properties of POE before and after crosslinking were studied in this article. Multiple melting behaviors were found for POE after silane crosslinking by using DSC measurement. Degree of crystallization of silane‐crosslinked POE decreases from 18.0 to 14.3%, with increase of VTMS from 0 to 2.0 phr. Tensile strength of silane‐crosslinked POE reaches a maximum of 28.4 MPa when concentration of VTMS is 1.5 phr, while elongation at break is 487%. TG shows that the temperature of 10% weight loss for pure POE is 405°C, while for crosslinked POE with addition of 2.0 phr VTMS the value comes to 452°C, indicating that crosslinking significantly help improve the thermal stability of POE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5057–5061, 2006     

Characterization of polyvinyl alcohol/gelatin blend hydrogel films for biomedical applications

In the present investigation, attempt was made to prepare blend hydrogel by esterification of polyvinyl alcohol with gelatin. The blend hydrogel was further converted into films by the conventional solution‐casting method. These films were characterized by FTIR, DSC, and X‐ray diffraction studies. The refractive index and viscosity of different composition of the blends were measured in the solution phase of the material. The mechanical properties of the blend films were measured by tensile test. Swelling behavior of the blend hydrogel was also studied. The FTIR spectrum of the blend film indicated complete esterification of the free carboxylic group of gelatin. The DSC results indicate that the addition of gelatin with PVA changes the thermal behavior like melting temperature of PVA, which may be due to the miscibility of PVA with gelatin. The interaction of gelatin with PVA molecule changes the crystallite parameters and the degree of crystallinity. The crystallinity of the blend film was mainly due to gelatin. The comparison of viscosity indicated an increase in the segment density within the molecular coil. The results revealed the changes observed in the properties of the gel, and it enhances the gel formation at viscoelastic phase of the material. The blend film had sufficient strength and water‐holding capacity. The results obtained indicated that the blend film could be used for various biomedical applications such as wound dressing and drug‐delivery systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanism of paper wet strength development by polycarboxylic acids with different molecular weight and glutaraldehyde/poly(vinyl alcohol)

In our previous research, we found that crosslinking paper using poly(carboxylic acid)s with different molecular weight or using the combination of glutaraldehyde and poly(vinyl alcohol) (PVA) significantly improved the wet strength of the paper. In this research, we studied the mechanism of paper wet strength development using crosslinking systems with different molecular weight by measuring scanning electron microscopic (SEM) images, wet strength, folding endurance, wet thickness, water retention, and Z‐direction tensile strength of the treated paper. The paper crosslinked by a high‐molecular weight (MW) poly(carboxylic acid) shows more swelling by water than that crosslinked by a low‐MW polycarboxylic acid in the SEM micrographs even though both treated paper samples have similar wet strength. Thus, the data suggest that high‐MW poly(carboxylic acid)s promote the formation of interfiber crosslinking. Crosslinking paper by glutaraldehyde, a crosslinking agent of small molecular size, improves wet strength and reduces flexibility and swellability of paper because of the formation of intrafiber crosslinking. Combining glutaraldehyde with PVA as a coreactant increases wet strength and also retains flexibility and swellability of the treated paper because of the formation of interfiber crosslinking. The hypothesis that PVA reacts with glutaraldehyde to form a polymeric pentanedialated‐PVA crosslinking system and promotes the formation of interfiber crosslinking on the paper is supported by the data of wet strength, folding endurance, wet thickness, water retention, and Z‐direction tensile strength of the treated paper. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 277–284, 2006     

Dissolution and Enzymatic Degradation Studies Before and After Artificial Ageing of Silk‐ or Linen‐Reinforced Gelatin Laminates, 2

Biodegradable laminates based on gelatin and on gelatin/starch blend reinforced with fabrics (silk or linen) were prepared by melt pressing. Due to crosslinking during the thermal treatment and in some cases, to additional crosslinking with methylenedi(p‐phenyl) diisocyanate, the fresh and artificially aged samples demonstrated improved mechanical properties, as reported previously. In Part 1 of this study on the environmental behavior of these new laminated composites, the simple dissolution in a buffer solution or water of fresh and artificially aged samples was considered. During this treatment soluble, i.e., uncrosslinked molecules were removed leaving a product resulting from addition reactions and consequent crosslinking. These processes take place during the melt pressing at 180 °C and cause a decreased solubility of gelatin. The present Part 2 deals with the enzymatic treatment of the same samples. We have implicitly shown that the gelatin moiety of the laminates undergoes proteolysis and that this process depends on the laminate composition. At the end of the treatment the enzymatic buffer solution contains only peptides and virtually no high‐molecular gelatin. The degrees of degradation vs. time dependencies differ for water and enzymatic treatment of the samples, indicating different processes in either treatment. The time‐course curves of the enzymatic treatment of different laminates and the kinetic parameters derived therefrom were analyzed. Thereby the effect of many factors on the accessibility of the gelatin moiety to proteolysis was shown. These factors are: temperature treatment, artificial ageing, the nature of the reinforcing fabrics, the “additional” crosslinking with methylenedi(p‐phenyl) diisocyanate, etc. The gelatin‐linen laminate is the most sensitive to crosslinking. There is a tendency that the crosslinking smears the differences in the time‐course of the absorption behavior curves of the different samples.

Degree of degradation, β′, (related to only the gelatin) vs. time, t, for laminates: (a) uncrosslinked gelatin‐linen; (b) crosslinked gelatin‐linen; (c) uncrosslinked gelatin‐silk; (d) crosslinked gelatin‐silk.     

Synthesis of sulfonated rubber ionomers by the ring‐opening reaction of epoxidized styrene–butadiene rubber,their characterization,and their properties

A novel method for the synthesis of the sulfonate ionomer of styrene‐co‐butadiene rubber (SBR) was developed. SBR was first epoxidized by performic acid formed from hydrogen peroxide and formic acid in situ in solution, and this was followed by a ring‐opening reaction with an aqueous solution of NaHSO₃. The optimum conditions for the epoxidation of SBR in the presence of a phase‐transfer catalyst and for the ring‐opening reaction of epoxidized SBR with an aqueous solution of NaHSO₃ were studied. During the epoxidation of SBR, a phase‐transfer catalyst, such as poly(ethylene glycol), could enhance the conversion of double bonds to epoxy groups. During the ring‐opening reaction, both the phase‐transfer catalyst and ring‐opening catalyst were necessary to enhance the conversion of the epoxy groups to ionic groups. The addition of Na₂SO₃ to the reaction mixture was important to obtain 100% conversion. The products were characterized with Fourier transform infrared spectrophotometry, ¹H‐NMR spectroscopy, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). DSC showed that the sodium sulfonate SBR ionomer possessed a dissociation temperature of ionic domains at 110°C, which appeared as black spots under TEM, after the sodium ions of the ionomer were substituted by lead ions. Some properties of the sodium ionomer, such as the water absorbency, oil absorbency, and dilute solution behavior, were studied. With increasing ionic groups, the water absorbency of the ionomer increased, whereas the oil absorbency decreased. The dilute solution viscosity of the ionomer increased abruptly with increasing ionic group content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3090–3096, 2006     

Rheological and mechanical properties of cross-linked fish gelatins

Gelatin was extracted from the skins of Alaska pollock (Theragra chalcogramma) and Alaska pink salmon (Oncorhynchus gorbuscha). Amino acid analysis and gel electrophoresis were used to determine their amino acid composition and molecular weight profiles, respectively. Dynamic rheology was also used to characterize the fish gelatins’ gelation and melting behavior as well as their cross-linking behavior upon adding genipin and glutaraldehyde. Pollock and salmon gelatin had lower gelation and melting temperatures than that of a commercial porcine gelatin. Both fish gelatins that contained genipin showed faster cross-linking rates for samples with higher pH values. However, salmon samples exhibited greater dependence on pH. Also, pollock gelatin cross-linked faster with glutaraldehyde than with genipin. After five days of cross-linking, all porcine samples had much greater gel strengths than pollock samples. In addition, porcine samples containing genipin had gel strengths several times greater than those containing glutaraldehyde.     

Characterization of strong polyelectrolyte hydrogels based on poly(vinyl alcohol)

Maleic anhydride (MA) was grafted onto both partially and fully hydrolyzed poly(vinyl alcohol) (PVA) in the presence of an initiator. Strong polyelectrolyte polymers were prepared by sulfonation of PVA–MA grafts. The sulfonation was completed by reaction of hydroxyl groups of PVA–MA grafts with two different sulfonating reagents (chlorosulfonic acid and pyridine sulfonic acid). The sulfonation degree was evaluated by acid–base titration and ¹H NMR analysis. The solution behaviour of the prepared grafts was evaluated from viscosity measurements. Four kinds of water‐insoluble PVA–MA and PVA–MA‐SO₃H hydrogels were prepared by heat treatment, physical gelation and chemical crosslinking with different weight ratios of N,N‐methylene bisacrylamide (MBA) crosslinker. The swelling parameters were measured for all prepared gels in deionized water and aqueous solutions at different pH values from 2 to 12 having constant ionic strength (I = 0.1). All gels exhibit a different swelling behaviour upon environmental pH changes. Copyright © 2004 Society of Chemical Industry     

Water state in chemically and physically crosslinked chitosan membranes

Chemically and physically crosslinked chitosan membranes were prepared by treating chitosan (Ch) with glutaraldehyde (GA) and sulfuric acid (SA). FTIR and XRD results were employed to confirm the formation of covalent and ionic crosslinks between Ch, GA, and SA. The states of water in non‐crosslinked and covalently and ionically crosslinked chitosan membranes containing different amount of water were investigated by low temperature differential scanning calorimetry measurements. The equilibrium swelling in water was examined gravimetrically. Two types of water were found in the polymer samples, i.e., freezing water and non‐freezing water. The effect of crosslinking process on water state and water uptake was analyzed. The water uptake decreased after chitosan crosslinking with GA, but significantly increased after later crosslinking with SA. The amount of non‐freezing water was generally smaller in crosslinked membranes. An impact of molecular and supermolecular structure on water uptake and state of water in non‐crosslinked and crosslinked chitosan membranes was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1707–1715, 2013