Influence of Hydroxyvalerate Content on the Crystallization Kinetics of Poly(hydroxybutyrate-co-hydroxyvalerate)

Abstract

Influence of hydroxyvalerate (HV) content on the crystallization kinetics of hydroxybutyrate (HB) units in random poly(hydroxybutyrate-co-hydroxyvalerate) (P(HB-co-HV)) copolymers has been studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that the crystallization kinetics of HB units was strongly affected by the presence of the ethyl side chain of HV units whether under the non-isothermal or isothermal crystallization conditions. The spherulitic growth rate (G) and overallall crystallization rate (kn) of HB units decreased with increasing HV content. Both G and kn exhibited the maxima, Gmax and knmax , which showed a gradual shift toward lower temperatures with increasing HV content, which may be attributed to the depression in the equilibrium melting point (Tm0) and nucleation factor (Kg). The temperature corresponding knmax was different from Gmax due to the depression of nucleation rate with the degree of undercooling was more susceptible than that of the growth rate. According to the Lauritzen–Hoffman theory of secondary nucleation, the crystallization of HB units in P(HB-co-HV) copolymers was similar to that of neat PHB as regime III and n=4 growth process.