N-乙基壳聚糖的针状结晶

NEEDLE-LIKE CRYSTALS OF N-ETHYL CHITOSAN

在N 乙基壳聚糖的甲酸溶液浇铸膜中观察到高分子少有的针状晶体 .从球晶经后结晶得到的针状晶体为长条矩形 ,典型尺寸为～ 5 0 μm× 2～ 5 μm× 1～ 2 μm ,高分子链平行于晶体长轴 .针状晶体首先出现在球晶的核心处 ,继而出现在球晶微纤每个树枝状分叉处 ,最后才遍布球晶各处 .针状晶体可以看成是高分子伸直链结晶的一种 .浇铸膜吸潮实际上形成了超浓溶液 (浓度 >80wt% ) 。

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.