The synergistic effect of zinc oxide and phenylphosphonic acid zinc salt on the crystallization behavior of poly (lactic acid)

In order to improve the crystallinity and crystallization rate of poly (lactic acid) (PLA), a method for the preparation of a composite nucleating agent (CNA) consisting of zinc oxide and phenylphosphonic acid zinc salt was proposed. Zinc oxide, phenylphosphonic acid zinc salt and CNA were mixed into PLA through the melt blending method, respectively. The resultant PLA samples were characterized by differential scan calorimeter (DSC) and polarized optical microscope (POM). The DSC results showed that the crystallinity and crystallization temperature of the PLA samples with CNA were higher than those of the other PLA samples. The phenomena of crystallization nucleation and growth of various PLA samples were observed by means of POM. Isothermal and non-isothermal crystallization behavior of various PLA samples with different addition of CNA was studied, the corresponding result showed that the overall crystallinity, crystallization rate, nucleation density, and spherulite number increased obviously, as well as the crystallization time decreased, indicating the heterogeneous nucleating effect of CNA on the crystallization of PLA. For each of the component of CNA, the phenylphosphonic acid zinc salt could be used as an effective site of heterogeneous nucleation, resulting in the increasing nucleation density of PLA, and the zinc oxide could be acted as a good crystallization promoter for promoting the crystal growth of PLA. At the CNA content of 1 phr, CNA had a significant impact on crystallization behavior of PLA with a little negative influence on the molecular weight of PLA.