Solid state structure of chitosan prepared under different N-deacetylating conditions

Changes in the crystallinity and polymorphic nature of chitosan, as a function of N-deacetylation of chitin under different conditions were studied. Viscosity average molecular weight suggests a higher degree of polymerization (DP) for chitosan prepared in the presence of thiophenol, as an oxygen scavenger. FT-IR spectra exhibited a progressive weakening of the bands at 1655, 3265 and 3100 cm−1 during N-deacetylation and A1382/A2920 cm−1 ratios of 0.65, 0.56 and 0.46 indicated a higher order structure for chitosan prepared with thiophenol than those prepared under N2 atmosphere or otherwise. The differences in crystallinity indices of chitosans were further substantiated by X-ray diffraction data. Splitting of C1 and C4 signals in CP-MAS 13C NMR spectra suggested the possible occurrence of newer conformational polymorphs. DSC thermograms showed higher thermal stability for chitosan with higher DP.