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Cross-Linked Chitosan/Chitin Crystal Nanocomposites with Improved Permeation Selectivity and pH Stability Aji P. Mathew,*,† Marie-Pierre G. Laborie,‡ and Kristiina Oksman† Division of Manufacturing and Design of Wood and Bionanocomposites, Luleå University of Technology, SE-93187 Skellefteå, Sweden, and Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington 99164-1806 Received February 19, 2009; Revised Manuscript Received April 6, 2009
This study is aimed at developing and characterizing cross-linked bionanocomposites for membrane applications using chitosan as the matrix, chitin nanocrystals as the functional phase, and gluteraldehyde as the cross-linker. The nanocomposites’ chemistry and morphology were examined by estimation of gel content, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and atomic force microscopy (AFM), whereby the occurrence of cross-linking and nanoscale dispersion of chitin in the matrix was confirmed. Besides, cross-linking and chitin whiskers content were both found to impact the water uptake mechanism. Cross-linking provided dimensional stability in acidic medium and significantly decreased the equilibrium water uptake. Incorporation of chitin nanocrystals provided increased permeation selectivity to chitosan in neutral and acidic medium.
1. Introduction Nanoreinforcements have the potential to improve the water vapor permeability, mechanical properties, and thermal stability of biopolymers without significantly affecting the transparency of the biopolymers.1,2 However, for such property improvement to occur, the nanowhiskers need to be uniformly dispersed in the matrix. The dispersion of nanocrystals in the matrix is a function of the matrix/reinforcement compatibility and of the manufacturing method. Cellulose nanoreinforcements, in the form of stiff highly crystalline nanowhiskers, are most commonly used to reinforce biopolymers.2,3 Many researchers have shown that incorporating a few percentages (1-10%) of cellulose nanocrystals into polymer matrices can induce vast improvement in properties due to their small size and large surface area.2-6 After cellulose, chitin is the most abundant natural polysaccharide in the world, the main source being marine crustaceans like shrimps and crabs.7 Chitin is a linear polysaccharide composed of β-(1-4)-linked units of linked units of N-acetyl2-amino-2-deoxy-D-glucose.8 In natural chitin, it is believed that a small proportion of these units are deacetylated. Chitin polymers form highly crystalline networks, the R-polymorph being more common and stable than the β-polymorph. Due to its insolubility in most solvents, chitin has found few applications to date.9 However, chitin whiskers have been successfully prepared by Marchessault as early as 195910 and by Dufresne and co-workers who used them as reinforcements in polymers.11-13 In contrast, chitosan, the product of extensive deacetylation of chitin is soluble in dilute acid solutions and has found many applications in the biomedical, cosmetics and agriculture fields.9 Depending on the degree of deacetylation, chitosan contains various proportions of β-(1-4)-linked units of 2-amino-2-deoxyD-glucose, and N-acetyl-2-amino-2-deoxy-D-glucose. A major difference between chitosan and chitin therefore resides in the * To whom correspondence should be addressed. E-mail: aji.mathew@ ltu.se. † Luleå University of Technology. ‡ Washington State University.
abundant free amino groups on chitosan compared to chitin that confer to the former a much greater reactivity. Chitosan is most often amorphous and can be processed into flexible films. Besides, chitosan is bioactive, biocompatible, nontoxic, and therefore find applications in pharmaceutical and biomedical products in the form of films, beads or spheres, cross-linked gels, and so on.14-17 The use of chitosan membranes in water ethanol pervaporation, enzyme immobilization, metal ions removal, protein separation, and so on has also been explored.18-21 For such applications, chemical resistance and mechanical strength are commonly improved by cross-linking. Reinforcement of chitosan with chitin nanocrystals is another interesting method to improve the mechanical properties, permeation selectivity, and thermal stability of chitosan without affecting biodegradability, biocompatibility, and antibacterial properties. For example, Sriupayo et al. reported the preparation of chitosan/ chitin nanocomposite films where heat treatments of the films were used to increase water resistance.22 Incorporation of chitin nanocrystals resulted in an improvement in tensile properties and water resistance. The goal of the present study is to further exploit the potential of chitin/chitosan nanocomposites as barrier layers with higher permeation selectivity, dimensional stability, and pH resistance. The chitin nanocrystals act as a multifunctional nanomaterial that provides reinforcement as well as enhanced permeation selectivity. It was hypothesized that for such nanocomposites chemical cross-linking should further enhance the barrier properties, water resistance, and stability to acidic conditions. In particular, this work evaluates the impact of chitin nanocrystals loading and gluteraldehyde cross-linking on the nanocomposite morphology, chemistry and barrier properties utilizing analytical methods such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and water sorption studies.
2. Experimental Section 2.1. Materials. Chitosan obtained by Cognis GmbH (Germany) with 81% deacetylation (Chitopharm M, Mw ) 100000-2000000) was used
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Table 1. Material Compositions and Sample Codes sample code
chitosan (%)
Ch Ch-CC5 Ch-CC10 XCh XCh-CC5 XCh-CC10
100 95 90 100 95 90
chitin (%) 5 10 5 10
as the matrix phase. Crab shell chitin in form of flakes was purchased from Sigma-Aldrich GmbH (Germany) and used to produce chitin nanocrystals (CC). Glutaraldehyde solution 50%, purchased from Sigma-Aldrich GmbH (Germany), was used to cross-link components of the bionanocomposites. Other chemicals, including potassium hydroxide, sodium hydroxide, glacial acetic acid 100%, hydrochloric acid 32% (HCl), and so on, were purchased from Merck KGaA 64271 Darmstadt (Germany) and used as received. 2.1.1. Preparation of Chitin Nanocrystals. Chitin nanocrystals were produced by using the procedure reported by Nair and Dufresne et al.11 The source material was first treated with 5% KOH for 6 h to remove the protein matter. It was then washed with distilled water and bleached with chlorite for 6 h at 80 °C with intermediate rinsing using distilled water. Following the bleaching step, the suspensions were kept in 5 wt % KOH solution overnight, washed with distilled water, and concentrated by centrifugation. The protein-free bleached chitin was hydrolyzed using 3 N hydrochloric acid at 80 °C for 90 min. After hydrolysis, the suspension was neutralized by diluting with distilled water and centrifugation. The neutralization was completed by dialyzing against distilled water for 7 days. The neutralized nanocrystal suspensions were dispersed further by ultrasonic treatment for 5 min at 24 kHz using a ultrasonic processor (UP400S, Heilscher). The whisker suspensions when viewed under cross polarized light showed flow birefringence, supporting the existence of chitin nanocrystals. 2.1.2. Preparation of Chitosan/Chitin Nanocomposites Films. A dilute solution of chitosan was first prepared by adding 2 wt % chitosan powder in a 2 vol % acetic acid solution and stirring for 12 h at 45 °C. Chitin nanocrystals/chitosan solutions were then prepared by adding various amounts of a 3 wt % aqueous dispersion of chitin nanocrystals in the dilute chitosan solution so as to yield 5 and 10 wt % of chitin crystals in the chitosan matrix. The mixtures were then stirred for 12 h to ensure proper mixing. The prepared formulations with 0, 5, and 10 wt % chitin nanocrystals were sonicated (UP400S, Heilscher) at 24 kHz, for 5 min prior to casting on well-dried polystyrene Petri dishes. The formulations were left to evaporate in a vacuum oven at 45 °C for 48 h. The dried films had a thickness of 0.05-0.08 mm and a total dry weight of 0.5 g. These films were further neutralized by immersing in 1 M NaOH and then repeatedly washed with distilled water and allowed to dry at room temperature. 2.1.3. Cross-Linking of Chitosan and Chitosan/Chitin Nanocomposite Films. Chitosan films and chitin/chitosan nanocomposites were treated with a gluteraldehyde solution to induce cross-linking via the constituents’ reactive groups (amine, amide, and hydroxyl). Waterconditioned membranes were kept immersed in a 0.02% (w/v) gluteraldehyde solution for 48 h at room temperature and then washed with distilled water and dried in air at room temperature. The prepared material compositions and the sample codes used are summarized in Table 1. 2.2. Characterization. 2.2.1. Fourier Transform Infrared Spectroscopy. Fourier transform infrared spectroscopy (FT-IR) was performed using a Nicolet Avatar 370 DTGS with an attenuated total reflectance cell (ATR). The crystal was a ZnSe and 128 scans were collected from 650 to 4000 cm-1 using a resolution of 4 cm-1. The autogain function was used and a background was collected before each sample. For each specimen, at least four replicate spectra were acquired. The spectra were first ATR corrected and then baseline corrected using a linear extrapolation. Finally, an average spectrum of the four or more replicates was processed and quantitative measurements were performed on the average spectra.
2.2.2. Gel Content. While chitin is not soluble in acetic acid, chitosan will dissolve in dilute acetic acid solutions unless it is cross-linked. To evaluate the success of the cross-linking step in chitosan and in the nanocomposites, the gel content of the films treated with the gluteraldehyde solution was determined via Soxhlet extraction with acetic acid. The nanocomposite samples were dried, weighed, and extracted with 2% acetic acid solution for 3 days as per ASTM 2765.23 After the extraction, the samples were dried and reweighed. The gel content was calculated using the following equation
extract% ) ((weight lost during extraction lost during extraction)/ (weight of original specimen - weight of filler)) × 100 (1) gel content ) 100 - extract%
(2)
2.2.3. X-ray Diffraction. X-ray diffraction (XRD) analysis was performed on powdered chitosan, chitin, cross-linked chitosan, and the nanocomposites before and after the cross-linking, using a Siemens D5000 X-ray diffractometer. The experiments were conducted at 40 kV and wavelength of 1.541 Å, from 5-40 degrees in steps of 0.02 degrees. 2.2.4. Microscopy. The fractured surfaces of the cross-linked and uncross-linked matrix and its nanocomposite films were studied in a JEOL, JSM-5200 scanning electron microscope (SEM). The films were fractured under liquid nitrogen and sputter-coated with gold. The films were observed in the SEM at an acceleration voltage of 20 kV. The chitin nanocrystals, as well as the nanocomposites, were characterized using a Veeco MultiMode atomic force microscope equipped with a Nanoscope V controller. For the analysis of nanocrystals, a droplet of the aqueous whisker suspension (0.5 wt %) was dried on a mica surface prior to AFM examination. The nanocomposite films were embedded in epoxy and ultra microtomed to obtain a smooth surface for the morphology studies. Overview images and detailed images for the nanocomposites were collected using a etched silicon tip in tapping mode, with a nominal spring constant of 5 N/m and a nominal frequency of 270 kHz. 2.2.5. Water Sorption Studies. The samples used for water sorption studies were circular discs with 20 mm in diameter and conditioned at 5% relative humidity. The initial disk weight and dimensions were first determined and kept immersed in distilled water at room temperature and conditions. The samples were removed at appropriate time intervals, gently blotted with tissue paper to remove excess water on the surface, and weighed again. This process was repeated until equilibrium swelling was reached as indicated by constant weight (about 300 h). The data collected were used for further calculations and analysis. In the case of sorption studies, in acidic medium, a 2 vol % acetic acid solution, at room conditions, was used. The sample dimensions and the experimental procedure were same as mentioned above.
3. Results and Discussion The chitosan and the nanocomposites prepared were in the form of thin films and had high optical clarity. It was interesting to note that the addition of 5 and 10 wt % of the chitin nanocrystals did not affect the optical clarity of the films significantly. In the case of the cross-linked matrix and nanocomposites, the films were also optically clear but showed a yellow-brown color. Earlier reports on cross-linked chitosan have shown that this coloration is characteristic of chitosan/ gluteraldehyde gels and is attributed to the formation of a chromophoric imine group (-NdC-) during cross-linking.24 3.1. FTIR Spectroscopy Analysis. The FTIR spectra were conducted on the chitin, uncross-linked and cross-linked chitosan, and the uncross-linked and cross-linked nanocomposite with 10 wt % chitin nanocrystals. An additional sample of crosslinked nanocomposites extracted with 2 vol % acetic acid was also studied with the aim to obtain a fingerprint of the crosslinked gel fraction. In Figure 1, the individual spectra of chitin,
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quantitatively detected with FTIR. If cross-linking does occur, it might mainly involve chitosan amino groups due to their greater reactivity and accessibility under homogeneous conditions. 3.2. Gel Content. To unambiguously evaluate the occurrence of cross-linking, the gel contents of the nanocomposites before and after gluteraldehyde treatment were determined by Soxhlet extraction with a dilute acetic acid solution. These values are summarized in Table 2.
Figure 1. ATR-FTIR spectra of (A) chitosan, (B) chitin, and (C) chitin/ chitosan nanocomposites before and (D) after the cross-linking and extraction steps.
chitosan, and of the nanocomposites (before and after the crosslinking steps) are compared. The spectral features in the hydroxyl and amide region of chitin indicate that it is of the most common R-allomorph.8,25 By comparing the FTIR spectra of the nanocomposites and of the components, it is clear that chitin is present in the nanocomposite before and after cross-linking as evidenced by its characteristics NH and OH stretch shoulder bands (3261 and 3106 cm-1, NH stretch; 3438 cm-1, OH stretch). This gives the primary evidence that the chitin nanocrystals are well integrated into the chitosan film during nanocomposite preparation and that they remain after the cross-linking step with gluteraldehyde and the extraction with acetic acid. The presence of both chitin and chitosan after extraction suggests that chitin nanocrystals are physically or chemically trapped in the chitosan matrix. To evaluate the occurrence of chemical cross-linking quantification of amide and imine bonds was undertaken. In chitosan, cross-linking with a dialdehyde is expected to occur primarily at the abundant amino sites yielding imine bonds that can be stabilized with the adjacent ethylenic double bonds.26 In fact, Oyrton et al. 1999 have monitored the cross-linking of chitosan with gluteraldehyde from the development of the imine bond (NdC) at 1655 cm-1 and of the ethylenic (CdC) bond at 1562 cm-1.26 At the same time they noted that the C-H stretch band increased (2940 cm-1) while no free aldehyde groups could be detected at 1720 cm-1 in the cross-linked material.26 Although less reactive and accessible due to the heterogeneous conditions, amide groups that are predominant on chitin could also theoretically react with gluteraldehyde resulting in intermolecular cross-linking. Cross-linking might therefore induce an increase in band intensity at 1655 cm-1 (chitin and chitosan amide I CdO stretch bands and possible imine bond) and a change in 1565 cm-1 band which combines the N-H bend bands (chitin amide II) of the constituents and the ethylenic band. The absorbance of these bands was thus measured and normalized to that of the polysaccharide C-O stretch at 1025 cm-1 to evaluate relative absorbance changes of the functional groups by reference to the chitin/chitosan backbones. Note however that after extraction of the nanocomposites, the 1565 cm-1 band was no longer present and therefore it was not quantified. The disappearance of that band indicated that the extraction altered the amide N-H bands arising from the chitin. No significant change in these band intensities was observed between the uncross-linked, cross-linked, and cross-linked/ extracted nanocomposites. It might be that cross-linking does not occur or that it occurs to such a small extent that it is not
As expected, chitosan matrix and the nanocomposites that had not been treated with gluteraldehyde dissolved completely in the hot 2% acetic acid solution. On the other hand, after treatment with gluteraldehyde, the chitosan matrix and the nanocomposites exhibited gel contents as high as 94-95%. This clearly supports the occurrence of cross-linking in the chitosan matrix and nanocomposites even though they could not be detected by FTIR. Irrespective of the chitin nanocrystals content, the nanocomposites’ gel content remain roughly constant, suggesting that chemical cross-linking rather than physical crosslinking from the chitin nanocrystals provided stability to water. 3.3. X-ray Analysis. The X-ray spectra for the raw materials, cross-linked matrix, and the nanocomposites are shown in Figure 2. Chitosan (a) exhibits a highly amorphous nature with broad and ill-defined signals at 2θ ) 9-10° and 18-20°. The chitin (b) shows a strong peak at 2θ ) 8.8 and 19° and shoulders at 2θ ) 20 and 22°, confirming its crystalline structure as R-chitin. As expected, the cross-linked chitosan (c) shows the same amorphous morphology as chitosan. In the uncross-linked (d) and cross-linked (e) chitosan/chitin nanocomposites the crystalline peaks corresponding to chitin are still visible (2θ ) 9.2 and 19.2°), indicating that chitin nanocrystals retain their crystalline morphology in the nanocomposites before and after cross-linking. There are no indications of changes in the matrix crystallinity with the addition of chitin nanocrystals. 3.4. Microscopy. 3.4.1. Chitin Nanocrystals. The structure and size distribution of the chitin nanocrystals were analyzed by AFM (Figure 3). The AFM image shows the presence of well isolated nanometer scale chitin crystals. As broadening effects due to the tip geometry may occur during scanning, the nanocrystal diameter was not determined from the AFM images27 but from height measurements, thanks to the Nanoscope V analysis software. Based on triplicate measurements, the diameter of chitin nanocrystals was found to vary between 13 and 20 nm. 3.4.2. Nanocomposites. Scanning electron microscopy images of the fractured surface of the un-cross-linked and cross-linked matrix and the corresponding nanocomposites with 10% nanocrystal content are given in Figure 4. These images give the overview of the matrix and composite morphology in a micrometer scale area. In the uncross-linked system there is no visible difference in the morphology between the matrix (Figure 4a) and the nanocomposite (Figure 4b) and in the cross-linked system the nanocomposite fracture surface (Figure 4d) is relatively rougher than the matrix (Figure 4c). The fracture surfaces of the uncrosslinked nanocomposite (Figure 4b) and cross-linked nanocomposite (4d) do not show any large agglomerates. This may be indicative of good adhesion between the matrix and the reinforcement, and the fracture has propagated through the matrix rather than through the chitosan-chitin interface. The absence of visible agglomerates in the nanocomposite may also indicate a uniform dispersion of chitin nanocrystals in chitosan. The phase images of the cross-linked and uncross-
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Table 2. Gel Content and Water Sorption Parameters of Chitosan-Chitin Nanocompositesa material Ch Ch-CC5 Ch-CC10 XCh XCh-CC5 XCh-CC10 a
gel content (%) water uptake (%) diff. coeff. (×107 cm2/s) sorp. coeff. (g/g) perm. coeff. (×107 cm2/s) acidic water uptake (%)
95 93 95
181 149 116 103 74 71
14.36 9.44 3.11 18.96 10.08 7.64
2.76 2.52 2.11 2.03 1.72 1.71
39.43 23.8 7.11 38.49 18.50 13.05
274 190 188
Water sorption data are based on two replicate measurements.
Figure 2. X-ray analysis data of (a) Ch, (b) chitin, (c) XCh, (d) ChCC10, and (e) XCh-CC 10.
linked nanocomposites were also obtained using atomic force microscopy (Figure 5).
Figure 5a,b shows the phase images of an uncross-linked nanocomposite with 5 and 10 wt % chitin nanocrystals, respectively. Figure 5c,d shows the phase images of a crosslinked nanocomposite with 5% and 10 wt % chitin nanocrystals. The lighter colored entities dispersed in the continuous phase correspond to the chitin nanocrystals embedded in the matrix phase. The images show a two-phased system with a uniform dispersion of chitin nanocrystals in random orientation. A denser distribution of nanocrystals in the 10% chitin nanocomposites compared to the 5% nanocomposites is also visible. The ridges and steps in the image may be caused by ultra microtoming. 3.5. Water Uptake Studies. 3.5.1. Water Sorption of Nanocomposites in Neutral Medium. The water sorption behavior of the chitosan and nanocomposites before and after cross-linking show a rapid initial water uptake (t > 2 min) followed by a leveling off region to an equilibrium value (Figure 6). It could be seen that the significant amount of the total water uptake in all the materials takes place during the first few minutes. While the equilibrium water uptakes (wt %) of chitosan reached 180%, it was reduced to 150 and 115% with the addition of 5 and 10% nanocrystals. Cross-linking more significantly reduced the equilibrium water uptake to 105% for the chitosan matrix and to 70% for the nanocomposites, regardless of chitin content. Therefore, cross-linking lowered the equilibrium water uptake to a greater extent than the incorporation of chitin in chitosan. 3.5.2. Water Sorption of Nanocomposites in Acidic Medium. Under acidic conditions, water sorption measurements could only be performed on cross-linked chitosan and nanocomposites that remained stable, whereas the uncross-linked films dissolved. As expected, the water uptake for the cross-linked matrix and the nanocomposites were higher in acidic medium compared to neutral medium (Table 2). As before, the incorporation of chitin crystals in the matrix significantly reduced the water
Figure 3. Atomic force microscopy of chitin nanocrystals (height and phase images).
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Figure 4. Scanning electron microscopy images of (a) Ch, (b) Ch-CC10, (c) XCh, and (d) XCh-CC10.
Figure 6. Plots showing the effect of chitin content and cross-linking on chitosan and chitin-based nanocomposites (shown up to 15 min only).
Figure 5. Atomic force microscopy images of (a) Ch-CC5, (b) ChCC10, (c) XCh-CC5, and (d) XCh-CC10.
swelling from 274% for cross-linked chitosan to approximately 190% for the nanocomposites having 5 or 10% whisker contents. This shows that cross-linking allows these chitosan nanocomposites to be used in acidic medium, while the chitin nanocrystals contribute to the perm-selectivity of the films. 3.5.3. Kinetics of Water Diffusion. The equilibrium water uptake by any polymeric system involves sorption, diffusion, and permeation processes. Sorption is a surface phenomenon and indicates the affinity of the material to water molecules, which is dependent on the chemical characteristics of the sample surface. Diffusion is the process where the penetrant moves through the polymer depending on the polymer relaxation process. The permeability represents the combined effect of the diffusivity as well as the solubility or sorptivity of the penetrant in a polymer. Besides, the uptake of any solvent by a polymeric system depends on the temperature, molecular weight and size of the
solvent molecule, the cross-linking density and composition of the nanocomposites, the polymer/solvent interaction, as well as the microstructure of the nanocomposites.28-31 Therefore, to understand the mechanism of water uptake in the chitosan and nanocomposites produced in this work, their response to sorption, diffusion, and permeation was studied in greater details. The coefficients for water diffusion, sorption and permeation s of the nanocomposites are shown in Table 2. It is clear that for both the cross-linked and uncross-linked systems, increasing content of chitin crystals reduced all the coefficients. The decrease in diffusion coefficient with increased chitin whisker content can be ascribed to resistance to water diffusion in the presence of nanocrystals. Permeability coefficient decreases with chitin nanocrystals content as they hinder the movement of water molecules between the polymer chains. It is, however, found that the diffusion coefficient values increased with cross-linking, whereas permeation values decreased after cross-linking. The sorption coefficient is influenced by the chemical characteristics and the addition of chitin nanocrystals to chitosan results in a material having numerous nanocrystals on the surface which has lower affinity and reactivity toward water. The NH2 groups are the most reactive species in the chitosan-chitin nanocomposites and with the addition of chitin nanocrystals there is a reduction in the number of amino groups on the surface to
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facilitate interaction with the water molecules. This effect is significant owing to the large surface area provided by this nanosized reinforcement. The sorption coefficient values decreased with cross-linking. In the cross-linked system the amino groups are being used up for the cross-linking process making the crosslinked sample surface less interactive with the water molecules. Therefore, the cross-linked nanocomposites have significantly lower sorption values owing to the combined effect of crosslinking and presence of chitin nanocrystals. The values of the diffusion, sorption and permeation coefficients given in Table 2 show that the uptake value follows the same trend as sorption coefficient rather than that of diffusion coefficient or permeation coefficient. This implies that sorption is the most prominent parameter that drives the water uptake by a chitosan-chitin nanocrystals system.
4. Conclusions Chitosan-based nanocomposite films containing chitin nanocrystals as functional components were successfully prepared and cross-linked using gluteraldehyde. The FTIR and gel content studies demonstrated the efficiency of the cross-linking as well as the presence of both chitin and chitosan in the cross-linked gel fraction. As evidenced by atomic force microscopy, the chitin nanocrystals were homogeneously dispersed in the chitosan matrix in the nanocomposites, which may be attributed to the good chemical compatibility between the chitosan and the chitin. With X-ray diffraction, it was further shown that chitin nanocrystals retained their crystallinity, and chitosan retained its amorphous characteristics in the nanocomposites. The water uptake studies showed that cross-linking and chitin incorporation in the chitosan matrix both decreased the equilibrium water uptake although cross-linking had a more pronounced impact on perm-selectivity and stability toward pH variations. Further analysis on the mechanism of water uptake showed that uptake rate was the maximum during the first few minutes and was mainly governed by the surface phenomenon of sorption. The development of nanocomposites with chitin nanocrystals can be considered as an efficient route to produce chitosan-based biomaterials with tailored permeation properties without affecting its inherent characteristics like biodegradability, transparency, and antibacterial properties. The data on the mechanical properties and thermal properties of these nanocomposites will be reported as the next step. Supporting Information Available. Absorbance ratios of IR imine (1656 cm-1) and ethylenic (1565 cm-1) bands normalized to the carbohydrate backbone band (1025 cm-1). The equations used for the calculation of diffusion, sorption, and permeation coefficients. This material is available free of charge via the Internet at http://pubs.acs.org.
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BM9002199
