Role of the heat treatment of partial melt recrystallization method on microstructure change and toughness of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)

Abstract

The microstructure of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] was regulated by the heat treatment of partial melt recrystallization method (PMRM) to improve its mechanical properties effectively. The structural changes and toughening mechanism of P(HB-co-HV) were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), scanning electron microscope (SEM) as well as dynamic mechanical analysis (DMA) experiments. The imperfect crystals of P(HB-co-HV) melted at 176 °C while the remaining perfect crystals recrystallized at the higher temperature (Tc = 120–150 °C). The results demonstrated that the HV units were easily to be excluded from the PHB crystal lattice in the P (HB-co-HV) recrystallization process, which promoted the crystal perfection of P(HB-co-HV) and improved the tensile strength and melting temperature. Furthermore, the heat treatment of PMRM reduced the molecular chain density and entanglement in the amorphous region and made the distribution of the tensile degree of the molecular chains more uniform, which was conducive to the sliding of lamellar crystals along the impact tensile direction, inducing plastic deformation. In addition, the heat treatment of P(HB-co-HV) via PMRM produced a large number of micropores, which was conducive to dispersing stress and improving its macroscopic toughness during the subsequent stretching process.