Transcrystallization kinetics at the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/hemp fibre interface

Transcrystallization of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) on hemp fibres was investigated using polarized optical microscopy. Nucleation and growth of crystals of the transcrystalline region (TCR) were measured during isothermal treatments of samples located in a hot stage. The nucleation rate, nucleation density at saturation and growth rate of the TCR, were determined at crystallization temperatures between 320 and 363 K.The growth rate of crystals in the TCR is the same as that of spherulites in the bulk. Nucleation at the hemp fibres was properly described in terms of the heterogeneous nucleation theory and the transcrystalline growth agrees with the kinetics theory of polymer crystallization. From the empirical data we determined that the interfacial free energy difference function of PHBV on hemp fibres is Δσ = 4.4 erg/cm2, lower than the one in the bulk. This indicates that the substrate is not neutral but contributes to the formation of the TCR.From the intensity of the depolarization light, measured under different cooling rates, we determined the activation energies for crystallization in the bulk and transcrystallization.