CHAPTER VI CROSSLINKING OF CHITOSAN WITH COTTON FABRIC

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1 CHAPTER VI CROSSLINKING OF CHITOSAN WITH COTTON FABRIC 6.1 Introduction The crosslinking of commercial chitosan with bioscoured cotton fabrics were carried out using acrylonitrile and acrylonitrile/acetone mixture to impart antibacterial activity. The modified samples were analyzed to confirm the crosslinking, antibacterial activity and washing durability. The results of chitosan and crosslinked cotton fabrics were systematically studied and critically discussed in the forthcoming headings. 6.2 Characterization of commercial chitosan FTIR studies The FTIR spectrum of chitosan is envisaged in Figure 6.1. The broad and strong absorption peak is observed at 3419 cm -1 corresponds to O-H and N-H stretching of chitosan [227]. The peaks at 1149, 1072 and 897 cm -1 can be clearly assigned to C-O stretching. The weak band of CH stretching of chitosan appears at 2929 cm -1. The characteristic absorption peaks of chitosan are observed at 1626, 1595 and 1352 cm -1 which assigned to the amide I, the amine NH 2 and amide III respectively [228]. 123

2 Figure 6.1: FTIR spectra of chitosan UV-Vis analysis The UV-Vis spectral studies were performed with mixture of chitosan in 1M acetic acid. The UV-Vis spectrum of CS is shown in Figure 6.2. The absorption peak for chitosan is observed at 230 nm [229]. Normally, the solar UV radiation is actually composed of three regions. They are UV-A ( nm), UV-B ( nm) and UV-C ( nm). As stated above, the chitosan absorption would be in the UV region between 200 and 290 nm. 124

3 Figure 6.2: UV-Vis spectra of chitosan Photoluminescence spectral analysis Figures 6.3, represents the room temperature photoluminescence spectrum of chitosan. The excitation wavelength used in the study is 325 nm. It is obviously seen that two bands appeared in the photoluminescence spectra of chitosan. In chitosan, the UV emission band was observed at nm [230] and a green emission band occurs at nm, which is due to the recombination of a photogenerated hole with a singly ionized oxygen vacancy [231]. 125

4 Figure 6.3: PL spectra of chitosan XRD analysis X-ray diffraction (XRD) is also used to measure the nature of the polymer and the extent of crystallinity present in the polymer sample. The X-ray diffraction spectra of chitosan are displayed in Figure 6.4. The graph represents two major peaks at 2θ=10, 20, which was the characteristic peak of chitosan [140] SEM analysis The surface morphology of the chitosan is displayed in Figure 6.5. SEM image of chitosan show a flat lamellar shaped appearance with exhibition of nonporous smooth surface [230]. 126

5 Figure 6.4: XRD spectra of chitosan Figure 6.5: SEM image of chitosan 127

6 6.2.6 Thermal analysis Thermo gravimetric analysis has been used widely to study all physical processes involving the weight changes. It is also used to investigate the thermal degradation, phase transitions and crystallization of polymers. The thermogravimetric curve of chitosan is depicted in Figure 6.6. The TG curve exhibits two weight loss regions between ºC and ºC. The first region exhibits a 7% weight loss, which is probably due to the evaporation of the water content, and second region shows a sharp 38% weight loss, which may be ascribed to the thermal degradation of the chitosan polymer [229]. The small weight loss 6.8% occurs at ºC corresponds to the departure of CO traces during combustion process. The DTG curve of CS exhibits a broad exothermic peak at 310 ºC [232], which is due to the decomposition of chitosan. The total mass loss at 1000 ºC was found to be 90 mass% Antibacterial activity Biocidal action requires interactions with the cell membrane of the microorganism, and this interaction is influenced by the size of the molecule, intensity of the functional group and the type of the used metal ion. Figure 6.7 shows the zone of inhibition of chitosan on Gram-positive bacteria S. aureus, S. pyogenes and Gram-negative bacteria E. coli, K. aerogenes. 128

7 Figure 6.6: TG/DTG curve of chitosan The amine groups of chitosan could become change under weak acid condition into the -NH3 + anion, which can interact with the cell wall of bacteria and hinder the growth of the microorganism [233]. The zones of inhibition of chitosan were observed as 37 mm, 36 mm, 31 mm and 46 mm for S. aureus, S. pyogenes, E. coli and K. aerogenes respectively. When compared to other bacteria Gram-negative bacterium K. aerogenes showed higher antibacterial activity (Table 6.1). Table 6.1: Zone of inhibition of Chitosan Sample Zone of inhibition (mm) Gram positive Gram negative S. aureus S. pyogenes E. coli K. aerogenes CS 37± ± ± ±

8 Figure 6.7: Inhibition zone of CS on (a) S. aureus, (b) S. pyogenes, (c) E. coli and (d) K. aerogenes 130

9 6.3 Characterization of chitosan crosslinked cotton fabric FTIR analysis The dried chitosan crosslinked fabrics were made into KBr pellets and analysed with the FTIR spectrometer. The spectral representation of AN-CS and AA-CS are shown in Figure 6.8. The band assignment of these samples is shown in Table 6.2. The band observed at 3420 cm -1 (Figure 6.8a) for AN-CS corresponding to OH stretching of cellulose [222]. The infrared bands in the region of 1162, 1112 and 1058 cm -1 corresponds to representative spectrum for native cotton fibres. The characteristic peaks at 1630, 1596 and 1351 cm -1 assigned to amide I, the amine and amide III absorption bands of chitosan, respectively [234]. And the peaks at 2359 and 2351 cm -1 correspond to C-N stretching vibration, which was caused by cyanoethylation reaction due to addition of acrylonitrile. This implies that the chitosan coated on cotton fabric had reacted with acrylonitrile. Figure 6.8b shows the IR spectrum of AA-CS sample. There were no effects observed due to acrylonitrile and acetone action on the chitosan crosslinked cotton fabric. A new band appeared at 2359 cm -1 (Fig. 6.8a) is due to the C-N asymmetric band stretching [235] was not appeared in the AA-CS sample (Fig. 6.8d) indicates that acetone addition not favoured the C N substitutions. 131

10 Table 6.2: Characteristic bands of chitosan crosslinked fabrics Sample Frequency cm -1 -OH and NH Primary amine (Amide I) Amide II stretching -C=O -NH stretching bending AN-CS C-N stretching 2341 & 2359 AA-CS Figure 6.8: FTIR spectra of (a) AN-CS and (b) AA-CS fabric 132

11 6.3.2 SEM morphology SEM photographs of crosslinked fabrics were shown in Figure 6.9. The surface of AN-CS sample is shown in Figure 6.9a. From the appearance of this sample, we can see that the change in the structure of fibre s surface is mandate for the comparison. The surface of fibre becomes very smooth and more bulky in nature. These changes in structure of cellulose fibres might be attributed to the excellent properties like high diffusion and good swelling. And the chitosan is uniformly coated on the surface of fabric. Figure. 6.9b shows the SEM photograph of AA-CS fabric. The surface of this sample shows like a resin coated bulky fibres and the high amount of chitosan is coated on the fibre when compared to AN-CS sample, this may be due to the formation of crosslink between acrylonitrile and acetone. The uniformity of swelling increases with addition of solvent Antibacterial activity Table 6.3 shows the zone of inhibition values of AN-CS and AA-CS on Gram-positive bacteria S. aureus, S. pyogenes and Gram-negative bacteria E. coli, K. aerogenes. The highest of 18mm and 27mm was observed for AN-CS and AA-CS on S. aureus. 133

12 (a) (b) Figure 6.9: SEM images of (a) AN-CS and (b) AA-CS fabric 134

13 Table 6.3: Zone of inhibition of chitosan crosslinked fabrics Samples AN-CS Zone of inhibition (mm) Gram positive Gram negative S. aureus S. pyogenes E. coli K. aerogenes 18± ± ± ±0.295 AA-CS 27± ± ± ±0.309 The bacteria S. aureus shows higher zone of inhibition than the bacteria E. coli which indicates that chitosan exhibits a stronger bactericidal effect upon Gram-positive than -negative bacteria [236]. In contrast, the S. pyogenes bacterium shows lower zone of inhibition than the K. aerogenes bacterium. It may be suggested that the antimicrobial effect is strongly dependent on the type of target microorganism [237]. The antibacterial activity of chitosan has been demonstrated almost exclusively in vitro; however, such results can hardly be extrapolated to textile goods, because interaction of chitosan with the fabric components will likely interfere with their efficacy. The AA-CS sample shows high antibacterial activity than AN-CS sample. Even though there was no evidence from FTIR spectra on the crosslink formation between chitosan and cotton cellulose, the AA-CS sample shows nearly same 135

14 results as obtained in AN-CS sample. This may be due to the deposit of polymer layer on the surface of the fabric (Figure 6.9b) which will contact bacteria easily. In this study, the Gram-negative bacteria showed more susceptibility than the Gram-positive bacteria for AN-CS and AA-CS samples. Lipopolysaccharides present in the outer membrane of Gram-negative bacteria contain anionic groups (phosphate, carboxyl), which contribute to the stability of the lipopolysaccharide layer through electrostatic interactions with divalent cations [238]. Removal of these cations by the more absorbing nature of crosslinked cotton fabric may be results in destabilization of the outer membrane through the release of lipopolysaccharide molecules [239] Washing durability The crosslinked samples were washed ten times and tested for their antibacterial properties after first and tenth wash. Table 6.4 shows the inhibition zone values of AN-CS and AA-CS on S. aureus bacterium. The result obtained indicates high permanency of the crosslinking even after ten washes (Figure 6.10). Table 6.4: Zone of inhibition values of the washed fabrics Bacteria Gram positive S. aureus Zone of inhibition (mm) AN-CS AA-CS 1 st wash 10 th wash 1 st wash 10 th wash 10± ± ± ±

15 Figure 6.10: Inhibition zone values of AN-CS fabric after (a) 1 st and (b) 10 th washes and AA-CS fabric after (c) 1 st and (d) 10 th washes 137

16 6.4. Conclusion The commercial chitosan was thoroughly characterized and crosslinked with cotton fabric using acrylonitrile and acrylonitrile/acetone mixture. FTIR, UV- Vis and PL spectrum confirms the presence of chitosan with respective characteristic peaks. XRD pattern also confirms the presence of chitosan with two major characteristic peaks. SEM image shows the nonporous smooth surface of chitosan. Thermal stability of the chitosan polymer occurs with moderate weight loss. When compared to other bacteria Gram-negative bacterium K. aerogenes showed higher antibacterial activity. The chitosan crosslinked fabric was confirmed by FTIR spectra with the characteristic groups of chitosan and nitrile peak. SEM also confirms the crosslinking by coating of higher amount of chitosan on the surface of fabric. The crosslinked fabric shows highest antibacterial activity on S. aureus. Even after ten washes, the crosslinked fabric retains the antibacterial activity. 138