Abstract: Being different from the literature results, the chemical reactivity of β-chitin was found to be poorer than that of α-chitin for O-propionylation reaction(basically a heterogeneous reaction). But the chemical reactivity of β-chitin was almost the same as that of α-chitin for N-acetylation reaction(a homogeneous reaction). The poor reactivity of β-chitin is explained by the higher crystallinity shown by the results of X-ray diffraction, the closer fibrillar structure shown by microscopy, and the higher stability of crystals shown by higher decomposition temperature in the thermogravimetric curves. After β-chitin was fibrillated by wet grinding, the O-propionylation reactivity increases evidently, but was still lower than that of α-chitin. Four levels of fibril structure can be distinguished in fibrillated β-chitin by polarized optical microscopy and scanning electron microscopy, i.e. fibrillar bundle, fibril, microfibril and elementary fibril with diameter in the order of 10¹, 10⁰, 10^-1 and 10^-2 μm respectively. Amodel for four levels of fibril structure of β-chitin is first suggested. Because more free hydroxyl groups are exposed on all levels of fibrils, the chemical reactivity of fibrillated β-chitin enhances.

Key words: Chitin, Chitosan, β-Chitin, Chemical reactivity