Morphological and Spectroscopic Studies of Chitin Nanowhiskers
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e 1. SEM micrograph of chitin solvated a) 2000x and b) 10 000x Figure 3 shows the SEM micrographs of FTS, where different structural formations are observed, in Figure 3a) flat and elongated shapes were found, in Figure 2b) spherules with diameters from 10-20 µm are exhibited. Finally, in Figure 3c) 5000x) and 3d) 2000x, exists continuous arranges, where from a core, leaves many branches. By comparing the FTM and FTS methods is appreciated that FTS provides more surface area, giving more sites for functionalization, which is positive for molecular bonds.
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Figure 2. SEM micrograph of FTM a) 2 000x, Figure 3. SEM micrograph of FTS a) 500x, b) 10 000x, c) 10 000x, d) 70 000x b) 500x, c) 5000x and d) 2000x.
SEM images show (Figure 3) that FTM and FTS methods produce flattened structures (nanofibers) and agglomerates with diameters around 30 nm and 15 µm respectively. However, with NanoSight instrument the diameters of nanoparticles were close to 92 and 68 nm for FTM and FTS respectively. It indicates that the FTS is a valuable method to obtain nanowhiskers because in a previous works (Zhao et al.) were obtained nanofibers with diameters from 25 to 120 nm using an Ultrasonic process. Also, chitin nanowhiskers have been obtained by acid hydrolysis with nanofibers with diameters from 2-5 nm where each nanofiber was composed of about 20 chains of N-acetyl-glucosamine [12]. Thus, it is considered that nanofibers obtained by FTM and FTS could contain about 525 and 380 chains of N-acetyl-glucosamine respectively. Infrared analysis Figure 4 shows a FTIR spectrum of a sample of solvated chitin. The region between 600 cm and 1700 cm-1 is defined as "fingerprint" in pure chitin, between 3542 cm-1 and 3084 cm-1 a -1
wide band of low intensity is associated with the OH and NH groups, at 2962 cm-1 the C-H group presents a symmetric vibration. A band corresponding to the C-O group presents a signal at 1675 cm-1. Furthermore, primary and secondary amide show signals at 1756 cm-1 and 1769 cm-1 respectively [13]. In previous studies, characteristics bands of chitin in solid phase corresponding to secondary amide are exhibited in the range of 1570-1575 cm-1. In the case of solvated chitin this band shows a significant displacement, as well as a loss of signal intensity, which can be associated with steric hindrance. It is caused by the interaction between polar groups as HN ··OH or HN···NH. The intense signal at 1404 cm-1 corresponds to CH groups in the structure of pure chitin, which may be associated with stretching OH groups or the acetyl group of the same structure (intramolecular stretching). Figure 5b exhibits the FTIR spectrum of FTM where is observed a characteristic band of secondary amides in the range of 3350-3180 cm-1. At 1671 cm-1 and 1626 cm-1 from the C=O partially overlaid on the NH bond is exhibited as a doublet. In general, lower intensities in relation to the CH peak are observed, which suggests there are impediments by associations among polar groups, it decrease the intensi
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