Needle-like crystals of N-ethyl chitosan
- 化学化工－已发表论文 
N-Ethyl chitosan (NECS) with degree of substitution 0.94 was prepared from chitosan and acetaldehyde. The films of NECS were prepared via the solution casting technique using formic acid as solvent. The crystalline structure and crystallization process were investigated by means of polarized optical microscopy, scanning electron microscopy and X-ray diffraction. Thousands of needle-like crystals, which are seldom found in polymers, were observed in NECS cast films after few days casting. The needle-like crystals were formed from spherulites through a psot-crystallization process. The shape of needle-like crystals was long rectangle with a typical size of similar to 50 mum (length) x 2 similar to 5 mum (width) x 1 similar to 2 mum (height) and molecular chains are parallel to the long axis of the needles. The needle-like crystals were first found on the centers of the spherulites, and then on every joint of dendritical fibrils of spherulites, at last on everywhere of spherulites. Generally speaking, the needle-like crystals basically oriented at the direction of radius of spherulites( also the direction of molecular chains)and decorated the spherulites. The possibility of post-crystallization was explained by the results that the cast films became super-concentrated solutions(>80%)after the adsorption of moisture because of the hydrophilic properties of NECS. The remained solvent and absorbed water were used as plasticizers, which increase the mobility of polymer chains. The dendritic crystals consisted of needle-like crystals were also found in the systems.