Crystallization behaviours of bacterially synthesized poly(hydroxyalkanoate)s in the presence of oxalamide compounds with different configurations

Bacterially synthesized poly(hydroxyalkanoate)s (PHAs) suffers from low crystallization rate which is enhanced by using tailor-made oxalamide compounds as nucleators. The influence of nucleator configurations on the crystallization behaviour of the PHAs was investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). The oxalamide compounds with ringy terminal structures (cyclohexyl and phenyl), notably the phenyl group, show higher nucleation efficiency and a better compatibility in the PHAs matrix, while the linear terminal structure (n-hexane) has poor nucleation effect. The crystallization temperature (Tc) and the crystallinity (Xc) of the PHAs are increased from 58 °C to 71 °C and from 5% to 48%, respectively, after addition of 0.75 wt% of the nucleator (phenyl group) upon cooling from the melt. Meanwhile, the half-life isothermal crystallization time (t0.5) of the PHAs at 110 °C is decreased by 70%. The oxalamide compounds increases the nuclei density of the PHAs accompanied with a reduction in spherulitic size. In addition, the crystal form and crystallization mechanism of the PHAs are not altered obviously after addition of the nulceators as confirmed by the POM, XRD and Avrami analysis.