S.-G. Hong*, and W.-M. Chen

 Department of Chemical Engineering and Materials Science, Yuan-Ze University, Chung-Li, 320, Taiwan, China

Keywords: polyhydroxybutyrate, surface, crystallization, ATR, nucleating agent

The surface crystallization behaviors of the polyhydroxybutyrate (PHB) and its copolymer with hydroxyvalerate (PHBV) under different processing conditions are studied with attenuated total reflection infrared spectroscopy (ATR) and differential scanning calorimetry (DSC). The PHB containing fumed silica and intercalated montmorillonite clay as the nucleating agent are also prepared. During the study, the hot-pressed specimens after quenching and annealing treatment at 120^oC are analyzed with ATR using internal reflection elements (IRE) of different penetration depths. The melting exotherms of treated specimens are also obtained from the dynamic DSC measurements. From the results of ATR, it is shown that the surface crystallinity of different PHB’s follows the similar trend as those in the bulk which are in the order of PHB > PHBV5 > PHBV12 and decrease with increasing the hydroxyvalerate content, and the outer surface layers have the higher crystallinity than the inner layers. The surface crystallinity obtained from different IRE’s follow the order of Ge(60^o) ~ KRS-5(60^o) >> KRS-5(45^o) and the crystallinity of the outmost surface layer about 0.9 micron thick is much greater than those about 1.7 microns deep. The surface crystallinity is significantly changed after annealing for all three polymers. After annealing, the surface crystallinity are changed to the order of KRS-5(60^o) > Ge(60^o) > KRS-5(45^o) and which is attributed to the effect of the surface energy on the reorganization of the outmost surface layer. In addition, the annealing time more than 17 hours changes the reorganization of the crystal lamellar more than changes the overall crystallinity. It is obtained from ATR and DSC analyses that the addition of filler decreases the crystallinity of the surface layer and the overall crystallinity of the bulk because of the formation of crystal with a much lower melting temperature and a lower lamellar thickness. The PHB with clay has a more pronounced effect in decreasing the crystallinity and a better consistency of the crystallization after annealing than with silica.     

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