C.-S. Liao*, C.-H. Hsu, and R.-D. Chang

Chemical Engineering Department, Yuan-Ze University, Taoyuan 320, Taiwan, China

Keywords: Polyhydroxyalkanoate, Nanocomposite, Saponite, Montmorillonite, Crystallization

      In order to increase the crystallization rate of biodegradable aliphatic polyester, polyhydroxybutyrate (PHB)/clay nanocomposites are prepared by solution mixing of PHB and alkylamino acid modified saponite or montmorillonite. X-ray diffraction methods and DSC thermal analysis are used to investigate the structural and thermal properties of PHB/clay nanocomposites. There are no apparent XRD peaks at 2q = 2-10° for PHB/clay nanocomposite with lower content of clay indicating that the d-spacing of intercalated layers is larger than 44Å. An exfoliated morphology with almost complete dispersion of the silicate layers is purposed for the present PHB/clay nanocomposites system. The crystallization and melting behavior of PHB/clay nanocomposites are characterized by various DSC analysis techniques. To analyze the crystallization kinetics in nanocomposites, the isothermal and non-isothermal crystallization analysis are performed. The overall kinetics of isothermal crystallization is analyzed with the overall rate constant and Avrami exponent. Under different constant cooling rate, a quasi-isothermal approach is applied for the discussion of non-isothermal crystallization. The addition of clay increases the crystallization rate and promotes the heterophase nucleation of PHB crystallites. In order to elucidate the effect of layered silicates on the crystalline morphology in nanocomposites, polarized micrographs of the PHB crystal growth under cooling are performed. The positive Maltese cross pattern is evident in the spherulites of pristine PHB and the size of spherulite decreases as the clay added into the PHB matrix. In summary, the exfoliated dispersion of clay acts as a nanoscale nucleating agent in PHB/clay nanocomposites. The crystallization rate of PHB is improved with a large magnitude of order. It will be benefited to fabricate the biodegradable products as bottles or packaging films.

      论文来源：International Symposium on Biological Polyesters ,Auguest 22-27, 2004