Abstract The catalytic degradation of chitosan (CS) using halloysite nanotubes-supported lanthanum(III) (HNT-La3+) catalysts have been studied. The HNT-La3+ catalysts with various amounts of La3+ (4.3 and 16.9 wt) were prepared by wet impregnation method and catalytic degradation of CS was carried out under different reaction conditions, i.e. amount of La3+ and degradation time. The catalysts and the degraded CS samples were then characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM/EDX), Fourier transform infrared (FTIR) spectroscopy, viscometry measurements, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and water solubility by UV–Vis spectroscopy. FT-IR showed that the degraded CS possessed different characteristics compared to CS. The degree of deacetylation (DD) increased for the degraded CS compared to that of pristine CS due to cleavage of peptide-like acetoamido (NHCOCH3) groups into free amine groups and loss of crystallinity. On the other hand, the viscosities and calculated viscosity average molecular weight, Mv decreased with increasing amount of La3+ and degradation time as a result of chain scission of the CS backbone. This resulted in an increase in the water solubility of the degraded CS. TGA results revealed that the degraded CS samples underwent degradation more readily than CS due to their lower thermal stabilities than CS. The appearance of the glass transition temperatures, Tg of the degraded CS samples at very low temperatures in the DSC curves indicated their low Mv.Graphic Abstract
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