C vegetal e chitin

C vegetal e chitin

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Preparation of Chitin/Cellulose Composite Gels and Films with Ionic Liquids Akihiko Takegawa, Masa-aki Murakami, Yoshiro Kaneko, Jun-ichi Kadokawa

PII: S0144-8617(09)00392-0 DOI: 10.1016/j.carbpol.2009.07.030 Reference:CARP 4303

To appear in:Carbohydrate Polymers

Received Date:26 May 2009 Revised Date:8 July 2009 Accepted Date:16 July 2009

Please cite this article as: Takegawa, A., Murakami, M-a., Kaneko, Y., Kadokawa, J-i., Preparation of Chitin/ Cellulose Composite Gels and Films with Ionic Liquids, Carbohydrate Polymers (2009), doi: 10.1016/j.carbpol. 2009.07.030

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Preparation of Chitin/CelluloseComposite Gels and 1 Films withIonic Liquids2

Akihiko Takegawa, Masa-aki Murakami, Yoshiro Kaneko, and Jun-ichi Kadokawa* 3

Department of Chemistry, Biotechnology, and Chemical Engineering, Graduate School of Science and 4 Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima 890-0065, Japan5

ABSTRACT7 In this study, we performedpreparation and characterizationsof the chitin/cellulose composite gelsand 8 filmsusing the two ionic liquids, 1-allyl-3-methylimidazolium bromide and 1-butyl-3-9 methylimidazolium chloride. First, chitin and cellulose were dissolved in each appropriate ionicliquid. 10 Then, the two liquidswere mixed in the desired ratios at 100oCto give the homogeneous mixtures. The 1 gels wereobtained by standing the mixturesfor 4 days. On the other hand, the films wereobtained by 12 casting the mixtureson glass plates, followed by soaking inwater and drying. The obtained gelsand 13 filmswere characterized by XRD and TGA measurements. The mechanical properties of the gels and 14 films were evaluated under compressive and tensile modes, respectively.15 16 Keywords: Chitin; Cellulose; Ionic liquid; Gel; Film17 18 * Corresponding author. Tel.: +81 9 285 7743; fax: +81 9 285 3253.19

E-mail address: kadokawa@eng.kagosima-u.ac.jp20

1. Introduction22 Polysaccharides are widely distributed in nature and have been regarded as structural materials and as 23 suppliers of water and energy(Stryer, 1995). They haveincreasingly been important because they 24 possess unique structures and properties being recently better understood, which are much different from 25 those of typical synthetic polymers. Of the many kinds of polysaccharides, cellulose and chitin are the 26 most important biomass resources; cellulose is the most abundant organic substance on earth and chitin 27 is the second most one.28

Cellulose consists of a chain of -(1 4)-linked glucose residues(Fig. 1) (Klemm, Heublein, Fink, & 29

Bohn, 2005). So far, the fundamental and practical studies on cellulose have been carried out, which 30 concern its structure, chemical and physical properties, biosynthesis, and morphology.Chitin is 31 structurally similar to cellulose, but it is an aminopolysaccharide having acetamidogroups at the C-2 32 positions in place of hydroxy groups in cellulose (Fig.1)(Muzzarelli, 1977). Despite its huge annual 3 production and easy accessibility, chitin still remains as an unutilized biomass resource primary because 34 of its intractable bulk structure, and thus, only limited attention has been paid to chitin, principally from 35 its biological properties(Muzzarelli, Jeuniaux, & Gooday, 1986). Although considerable efforts are still 36 being devoted to extend other novel applications to cellulose and chitinon the basis of the viewpoint for 37 efficient use as thebiomass resources, the lack of solubility of these polysaccharides in water and 38 common organic solvents causes difficulties in improving their processability, fusibility, and 39 functionality. The solubility problem is due to the stiff molecules and close chain packing via the 40 numerous inter-and intra-molecular hydrogen bonds caused by the hydroxygroups as well as the 41 acetamidogroups in the sugar residues. To date, only a limited number of solvent systems for cellulose 42 and chitin hadbeen found, for example, LiCl / N,N-dimethylacetamide system (Terbojevich, Cosani, 43 Conio, Ciferr, & Bianchi, 1985; Uragami, Ohsumi, & Sugihara, 1981) and NaOH / (thio)urea aqueous 4 solution (Hirano & Midorikawa, 1998; Zhang, Guo, & Du, 2002; Cai & Zhang, 2005) arewell-known as 45 the solventsfor these polysaccharides. In the previous publications, cellulose/chitin compositebeads,46 films,and membraneshave been prepared using these solvent systems(Zhang, Guo, & Du, 2002; Zheng, 47 Zhou, Du, & Zhang, 2002; Kondo, Kasai, & Brown Jr., 2004; Zhou, Zhang, & Guo, 2005; Liang, Zhang, 48 & Xu, 2007).49 It has been reported that a variety of room temperature ionic liquids can be used to dissolve cellulose50 (Liebert & Heinze, 2008; Feng & Chen, 2008). For example, it was found that 1-butyl-3-51 methylimidazolium chloride (BMIMCl, Fig.1) dissolved cellulose in relativelyhigh concentrations52 (Swatloski, Spear, Holbrey, & Rogers, 2002). In thefollowing papers by the same research group, the 53 cellulose films were further obtained by casting the solutions of cellulose in BMIMCl onto a glass plate, 54 followed by reconstitution by the addition of water(Turner, Spear, Holbrey, & Rogers, 2004; Turner, 5 Spear, Holbrey, Daly, & Rogers, 2005). We have alsostudied preparation of new materials using 56 cellulose and ionic liquids(Murakami, Kaneko, & Kadokawa, 2007; Kadokawa, Murakami, & Keneko, 57 2008a). As the recent result in the course of the work, we reported formation of agel from a solution of 58 cellulose in BMIMCl(Kadokawa, Murakami, & Kaneko, 2008b; Kadokawa, Murakami, Takegawa, & 59 Kaneko, 2009), which was obtained by keeping the solution at room temperature for several days. This 60 method for the preparation of the gel materials with ionic liquids has been extendedto other 61 polysaccharides such as carrageenan and guar gum (Prasad, Kaneko, & Kadokwa, 2009; Prasad, Izawa, 62 Kaneko, Kadokawa, 2009). On the other hand, only a few exampleshavebeen reported regarding the 63 dissolution of chitin with ionic liquids(Xie, Zhang, & Li, 2006; Mantz, Fox, Green I, Fylstra, DeLong, 64 &Trulove, 2007; Wu, Sasaki, Irie, & Sakurai, 2008). For the development of studies on chitin using the 65 ionic liquids, therefore, we have considered to find other ionic liquids which can dissolve chitin. Then, 6 the dissolution of chitin with the ionic liquids can be extended to the further work, e.g., the production 67 of new materials composed of chitin. 68 On the basis of the above viewpoints, recently,we found that an ionic liquid, 1-allyl-3-69 methylimidazolium bromide (AMIMBr, Fig. 1)) formed a clear liquid with chitin and evaluated its weak 70 gel nature by rheological analysis in a further work (Prasad et al., 2009). In the recent communication, 71 we also reported preparation and electrochemicalproperties of chitin/cellulosecomposite gel electrolyte72 containing binary ionic liquids with aqueous H2SO4for an electricdouble layer capacitor(Yamazaki et 73 al., 2009).The composite gel was prepared from a homogeneous mixture obtainedfroma liquid of 74 chitin with AMIMBr and a liquid of cellulose with BMIMClaccording to the similar method as that for 75 the aforementioned gel of cellulose with BMIMCl(Kadokawa, Murakami, &Kaneko, 2008b). 76 In this paper, we report the detailed study on the chitin/cellulosecomposite gels with the ionic liquids, 7 AMIMBr and BMIMCl,including characterization and mechanical property. Moreover, we also 78 describe preparation, characterization, and mechanicalproperty of the chitin/cellulosecompositefilms79 with the ionic liquids. The films were simply obtained by soaking the homogeneous mixtures of 80 chitin/cellulosewith AMIMBr/BMIMCl into water. 81 82

2. Experimental Section83 2.1. Materials84 Microcrystalline cellulose from Merck was used. Chitin powder from crab shells was purchased from 85 Nakalai Tesque, Inc. The degree of acetylation of the chitin sample was estimated by elementalanalysis 86 data to be 94.6 %, which was in good agreement with that of a standard chitin (Kurita, 2001)). An ionic 87 liquid, BMIMCl, was purchased from Sigma –Aldrich Co. An ionic liquid, AMIMBr wasprepared by 8 reaction of 1-methylimidazole with 3-bromo-1-propeneaccording to the method modified from the 89 literature procedure (Zhaoet al., 2005). 90

91 2.2.Preparation of chitin/cellulosecomposite gel with ionic liquids92 A typical experimental procedure for preparationof chitin/cellulosecomposite gel with ionic liquids 93 was as follows (chitin : cellulose = 1 : 3, mol/mol). Mixtures of chitin (0.0420 g, 0.206 mmol) with 94 AMIMBr (0.860 g, 4.24 mmol) and of cellulose (0.10 g, 0.617 mmol) withBMIMCl (1.0 g, 5.73 95 mmol) were independentlyheated at 100 oC for 24 hwith stirring to give clear liquidsof chitin (5 % 96 w/w) and cellulose (10 % w/w)in each ionic liquid,respectively. The two liquidswere mixed and 97 heated at 100 oC for 1 h with stirring to form a homogeneous mixture. The resulting mixturewas 98 transferred to an appropriate mold and it was kept standing at room temperature for 4 days to be a gel 9 form. The gel was taken out from a mold, soaked in acetone for 10 min, and dried under ambient 100 conditions to give a composite gel.101 102 2.3. Preparation of chitin/cellulosecomposite filmwith ionic liquids103 A typical experimental procedure forpreparation of chitin/cellulosecomposite film was asfollows. 104 The homogeneous mixtureof chitin and cellulose in the ionic liquids prepared as described above was 105 thinly cast on a glass plate. It was soaked in water and dried under reduced pressure to give a composite 106 film. 107

108 2.4. Determination of molar ratiosamong chitin, cellulose, AMIMBr, and BMIMClin gels and films.109 A weight of thegel or film sample was measured and the sample was subjectedto Soxhletextraction 110 with methanol for 5 h. A residual part was dried under reduced pressureand the molar amountsof chitin 1 and cellulosein the sample was calculated on the basis of a weight of the dried material and a feed ratio 112 of the two polysaccharides used for preparation of gel or film. The methanol extractwasevaporated and 113 dried under reduced pressure. Hydroquinone dimethylether as an internal standard was added to the 114 residue and the 1H NMR spectrum of the mixture was measured in CDCl3. The molar amountsof 115 AMIMBr and BMIMClin the sample was calculatedon thebasis of a weight of the residue and an 116 integrated ratio of the signals due to CH2= of AMIMBr, CH2-N of BMIMCl, and aromatic protons of the 117 internal standard. 118

119 2.5. Measurements120 XRD measurements were conducted using a Rigaku Geigerflex RADIIB diffractometer with Ni-121 filtered CuK radiation ( = 0.15418 nm). TGA measurements were performed on a SII TG/DTA 6200 122 at a heating rate of 10 oC / min. The stress-strain curves were measured using a tensile tester (Little 123

Senstar LSC-1/30, Tokyo Testing Machine Co.). NMR spectra were recorded on a JEOL ECX 400 124 spectrometer.125 126

3. Results and discussion127 The chitin/cellulosecomposite gels with ionic liquids wereprepared according to the similar 128 experimental manner as that for preparation of the gel of cellulose with BMIMCl(Fig. 2),described in 129 our previous publication(Kadokawa, Murakami, & Kaneko, 2008b). Since we had not found any ionic 130 liquids which had ability to dissolve both chitin and cellulose in sufficientconcentrations for the present 131 study, two kindsof the ionic liquids, i.e., AMIMBr and BMIMCl were used as follows. The clear liquids132 of chitin in AMIMBr (5 % w/w) and of cellulose in BMIMCl (10 % w/w) were independentlyprepared133 by heating each mixture at 100 oC for 24 h. We already confirmed in the previous literature that 134 deacetylation, degradation, and decreasing the molecular weight of chitin did not frequently occur 135 during the experiment for the formation of the 5 % w/w clear liquid with AMIMBr (Prasad et al., 2009). 136 Then, the two liquidsin desired ratios were mixed at 100 oC to form a homogeneous mixture. The 137 homogeneityof the mixturewas confirmed by observation usinga charge coupled device camera with 138 200 times magnification scale. Afterthe mixture was transferred to an appropriate moldandkept 139 standing at room temperature for 4 days, the formed gelwastaken out from the mold, soaked in acetone 140 for 10 min, and dried under ambient conditionsto give a composite gel.When the feed molarratios of 141 chitin to cellulose were 1 : 3–1 : 1, the gels were facilely formed. Increasing the molar ratio of chitin to 142 cellulose than 1 : 1did not give the gel formation. 143 The molar ratiosof each material in the gels were estimated as follows. First, the gelwas subjected to 144 Soxhlet extraction with methanolto extract the ionic liquids. The molar amountsof chitin and cellulose145 in the gelwerecalculated on the basis of a weight of the residual material and the feed ratio of the two 146 polysaccharides used for preparation of the gel. On the other hand, the methanol extract was147 concentrated and analyzed by the1H NMR measurement. The molar amountsof the two ionic liquids 148 were calculated by the integrated ratios of the 1H NMR spectrum using hydroquinone dimethylether as 149 an internal standard. On the basis of the above two calculations, the molar ratiosof chitin, cellulose, 150 AMIMBr, and BMIMClin the gelwere estimated, which were shown in Table 1.By comparing the ratio 151 of each material in the gel of run 1 in Table 1 (chitin : cellulose : AMIMBr : BMIMCl = 1 : 1 :19.5 : 152 9.7) with the correspondingfeed ratio (chitin : cellulose : AMIMBr : BMIMCl = 1 : 1: 20.0: 9.3) for 153 the gel preparation, it was suggestedthat little ionic liquids were leached out during the gelation process. 154 The data in Table 1 also indicatedthat the larger amounts of AMIMBrwere leached out during the 155 gelation process when the higher feed ratiosof the chitin liquidwith AMIMBr to the cellulose liquid 156 with BMIMClwere usedfor the gel preparation(run 2 and 3 in Table 1). 157 The XRD profilesof thegels in Fig. 3c-eexhibitedlittle diffractionpeaks due to the crystalline 158 structures of chitin and celluloseas observed in Fig. 3a-b. Figure4 shows the TGA curves of the gelsin 159 comparisonwith those of chitin and cellulose. The TGA curves of the gelsin Fig. 4c-e exhibited weight 160 losses starting at around 200 oC, which werealmost100 oC lower than those of chitin and cellulose in 161 Fig. 4a-b. These characterizations indicated that the crystalline structures of the polysaccharides were 162 not maintained in the gelsdue to good miscibility of the two polysaccharideswith the ionic liquids. The 163 TGA curves of the gels also showedweight losses of 12.9 –14.5 % at temperatures up to 100 oC, which 164 were reasonably explained by evaporation of water. These data suggested that the gels contained 165 relatively large amounts of water, and accordingly the followingsimilar gelation mechanism was 166 considered as that for the gel of cellulose with BMIMCl reported in our previous paper (Kadokawa, 167 Murakami, & Kaneko, 2008b). The present gels were gradually formed with absorption of water and 168 simultaneously exclusion of the excess ionic liquids. Thus, the aggregates of the polysaccharide chains 169 were formed during this process, which probably acted as cross-linking points for the gel formation.170 The stress-strain curves of the gels under compressive mode were measured,which are shown in Fig. 171 5. The fracture stresses and strains were 4.6 –130.0 kPa and13.0–14.1%, respectively. The 172 mechanical properties became more brittle with increasing the ratio of chitin in the gels.173 The chitin/cellulose films were further obtained by casting the homogeneous mixturesof 174 chitin/cellulosewith AMIMBr/BMIMClonto a glass plate, followed by reconstitution in water.First, the 175 chitin/cellulose homogeneous mixtures with AMIMBr/BMIMCl were preparedin the feed molarratios 176 of chitin to cellulose = 1 : 9 –1 : 3 according to the same procedure as that described above for the 177 preparation of the chitin/cellulose composite gels. Then, the homogeneous mixtures were thinly casted 178 on glass plates, which were soaked in water. The resulting gel-like materials were dried under reduced 179 pressure to give the chitin/cellulose composite films. Increasing the molar ratio of chitin to cellulose 180 than 1 : 3 didnot form the stable film. The molar ratiosof each materialin the films wereestimated by 181 the same method as thatfor the composite gels, which are listed in Table 2. In all the films, the molar 182 ratios of AMIMBr and BMIMCl to a repeating unit of chitin were less than 0.9and 2.5, respectively. 183 These data indicated that most of the ionic liquids used for the film preparation wereremoved by the184 above experimental procedure. 185 Figure6shows the XRD profiles of the composite films with differentchitin/cellulose ratios. When 186 themolarratio of chitin to cellulose was low (1 : 9), the diffraction peaks due to the crystalline 187 structures of the polysaccharides were hardlyobserved(Fig. 6f). With increasing the ratios of chitin to 188 cellulose, the small diffraction peaks due to the crystalline structure of chitin were appeared(Fig. 6c-e). 189 These resultsindicated that cellulose chains were more miscible with the ionic liquids to disruptthe 190 crystallinestructureand the chitinchains slightlyformed the crystallinestructure with increasingtheir191 contents in the films. The ratios of AMIMBr to BMMCl in the films werelower than those in feeds 192 when the higher ratios of chitin to cellulose were used (run 1 and 2 in Table 2). This result indicated that 193 AMIMBr was excluded prior to BMIMCl during the gelation under the conditions of run 1 and 2 in 194 Table 2. Therefore, the chitin chains might predominantly form the crystalline structure compared with 195 cellulose in the films with the higher contents of chitin. The TGA curve ofthefilm with the higher 196 chitin ratio to cellulose (1: 3) exhibited an onset of weight loss at around250 oC(Fig. 7c), which was ca. 197 30oC higher than that appeared in the TGA curve of the film with the lower chitin ratio to cellulose (1 : 198 9) (Fig. 7f). This differenceis explained by the crystallinity of the chitin chains in the films. Theabove 199 XRD and TGA results suggested that thetwo polysaccharides exhibited relatively good miscibility with 200 the ionic liquidsin thefilms although some crystalline structure of chitin was presence in the films with 201 the higher contents of chitin.The presence of the slight amounts of the ionic liquids probably 202 contributed to the miscibility of the two polysaccharides in the films.203 The stress-straincurves of the films in Fig. 8indicated that the mechanical properties became more 204 elastic with decreasing the ratiosof chitin to cellulosein the films. The fracture stresses and strains were 205 7.5 –9.0 MPa and 3.7 –1.0 %, respectively. 206 207 4. Conclusions208

209 In this paper, we reportedthe preparation and characterizationsof the chitin/cellulose composite gels210 and filmsusing the two ionic liquids, AMIMBr and BMIMCl. First, chitin and cellulose were dissolved 211 in each appropriate ionicliquid. Then, the two liquidswere mixed inthe desired ratios at 100oCto give 212 the homogeneous mixtures.The gels wereobtained by standing the mixturesfor 4 days. On the 213 other hand, the films wereobtained by casting the mixtureson glass plates, followed by soaking inwater 214 and drying. The obtained gelsand filmswere characterized by XRD and TGA measurements,which 215 showedrelatively good miscibilityamongthepolysaccharidesand the ionic liquids in the materials. The 216 mechanical properties of the gels and films were changed depending on theratios of chitin to cellulose 217 in the materials.218 219 Acknowledgments220 The authors acknowledgethe financial support from KRI Inc., Kyoto, Japan. 221 2

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Table 1. 305 Preparation and characterizations of chitin/cellulose composite gels with ionic liquids.306

RunMolar ratioin feedMolar ratio in gelFracture strain (kPa)Fracture strain (%)307

(chitin : cellulose : AMIMBr : BMIMCl)(compressive mode)308

Table 2. 313

Preparation and characterizations of chitin/cellulose composite films with ionic liquids.314

RunMolar ratio in feedMolar ratio in filmFracture strain (MPa)Fracture strain (%)315

(chitin : cellulose : AMIMBr : BMIMCl)(tensile mode)316

41 : 9 :19.7 : 76.51 : 9 : 0.43:

Figure Captions324

Fig. 1. Structures of chitin, cellulose, AMIMBr, and BMIMCl.325 Fig. 2. Preparation procedures for chitin/cellulose compositegels and films with ionic liquids326 Fig. 3.XRD profiles of chitin (a), cellulose (b), gels prepared in chitin/cellulose feed ratios of 1 : 1 (c), 327 1 : 2 (d), and 1 : 3 (e).328 Fig. 4. TGA curves of chitin (a), cellulose (b), gels prepared in chitin/cellulose feed ratios of 1 : 1 (c), 1 : 329 2 (d), and 1 : 3 (e).330 Fig. 5. Stress-strain curves under compressive mode of gels prepared in chitin/cellulose feed ratios of 1 : 331 1 (a), 1 : 2 (b), and 1 : 3 (c).332 Fig. 6. XRD profiles of chitin (a), cellulose (b), films prepared in chitin/cellulose feed ratios of 1 : 3 (c), 3 1 :5 (d), 1 : 7 (e), and 1 : 9 (f).334 Fig. 7. TGA curves of of chitin (a), cellulose (b), films prepared in chitin/cellulose feed ratios of 1 : 3 (c), 335 1 : 5 (d), 1 : 7 (e), and 1 : 9 (f).336 Fig. 8. Stress-strain curves under tensile mode of films prepared in chitin/cellulose feed ratios of 1 : 3 (a), 337 1 : 5 (b), 1 : 7 (c), and 1 : 9 (d).338

Br N


HO NHAc n Cl N

Cellulose n AMIMBr BMIMCl

Fig. 1

Fig. 2.

Fig. 3.

Fig. 4.

Stress (k

(b) (c)

Fig. 5.

Fig. 6. Fig. 7.

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