Spherulite morphology studies of N-alkyl chitosan films cast from formic acid solutions

The films of N-ethyl chitosan were prepared via the solution-casting technique with formic acid as a solvent. The solutions with different concentrations (35 and 40 wt %) were prepared previously from dilute solution (1 wt %) via evaporating process. The crystalline morphology of these films was investigated by means of polarized optical microscopy and scanning electron microscopy. Normal spherulites with a low growth rate formed in the casting films. The different morphologies of spherulite appeared in the films cast from the solutions with different concentrations. After further crystallizing for a few days, the spherulites were decorated by thousands of needlelike extended-chain crystals, which had a typical size of similar to50 mum (length) X 2similar to5 mum (width) X 1similar to2 mum (height) in the central part of the spherulite, but a typical size of similar to5 mum (lenght) x 1similar to2 mum (width) X 1similar to2 mum (height) in the fringe part of the spherulite. The real concentration for crystallization was determined to be 65-82 wt%. Thus, the crystallization actually appeared in supersaturated solution. (C) 2003 Wiley Periodicals, Inc.