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-hydroxyvalerate), PHV, is reported and compared to the companion bacterial polyester poly(beta-hydroxybutyrate), PHB. The equilibrium melting point, T0m, measured by the Hoffman-Weeks method is found to be 130-degrees-C. A glass transition temperature of -16-degrees-C is proposed as representative of amorphous PHV. Spherulitic growth kinetics are analyzed using the Lauritzen-Hoffman model, and kinetic parameters are extracted. Crystallization is found to occur within regime II. Melting and crystallization in blends of PHV with a copolymer P(HB-co-HV) containing 77 mol % HV are reported and discussed within the context of cocrystallization. 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.