MELTING AND CRYSTALLIZATION IN BACTERIAL POLY(BETA-HYDROXYVALERATE), PHV, AND BLENDS WITH POLY(BETA-HYDROXYBUTYRATE-CO-HYDROXYVALERATE)

The melting and crystallization behavior of bacterial poly(beta-hydrox yvalerate), PHV, is reported and compared to the companion bacterial p olyester poly(beta-hydroxybutyrate), PHB. The equilibrium melting poin t, T0m, measured by the Hoffman-Weeks method is found to be 130-degree s-C. A glass transition temperature of -16-degrees-C is proposed as re presentative of amorphous PHV. Spherulitic growth kinetics are analyze d using the Lauritzen-Hoffman model, and kinetic parameters are extrac ted. Crystallization is found to occur within regime II. Melting and c rystallization in blends of PHV with a copolymer P(HB-co-HV) containin g 77 mol % HV are reported and discussed within the context of cocryst allization. Finally, it is shown that PHV and PHB are phase separated in the melt. The implications of this result in terms of current views of isodimorphism in the P(HB-co-HV) system are discussed.