Thermal properties of blends of poly(hydroxybutyrate-co-hydroxyvalerate) and poly(styrene-co-acrylonitrile)

Thermal properties of blends of poly(hydroxybutyrate-co-hydroxyvalerate) (P HBV) and poly(styrene-co-acrylonitrile) (SAN) prepared by solution casting were investigated by differential scanning calorimetry. In the study of PHB V-SAN blends by differential scanning calorimetry, glass transition tempera ture and melting point of PHBV in the PHBV-SAN blends were almost unchanged compared with those of the pure PHBV. This result indicates that the blend s of PHBV and SAN are immiscible. However, crystallization temperature of t he PHBV in the blends decreased approximately 9-15 degrees. From the result s of the Avrami analysis of PHBV in the PHBV-SAN blends, crystallization ra te constant of PHBV in the PHBV-SAN blends decreased compared with that of the pure PHBV. From the above results, it is suggested that the nucleation of PHBV in the blends is suppressed by the addition of SAN. From the measur ed crystallization half time and degree of supercooling, interfacial free e nergy for the formation of heterogeneous nuclei of PHBV in the PHBV-SAN ble nds was calculated and found to be 2360 (mN/m)(3) for the pure PHBV and 292 0-3120 (mN/m)(3) for the blends. The values of interfacial free energy indi cate that heterogeneity of PHBV in the PHBV-SAN blends is deactivated by th e SAN. This result is consistent with the results of crystallization temper ature and crystallization rate constant of PHBV in the PHBV-SAN blends. (C) 2000 John Wiley & Sons, Inc.