Preparation and characterization of phosphorylated graphene oxide grafted with poly(L-lactide) and its effect on the crystallization, rheological behavior, and performance of poly (lactic acid)

Phosphorylated graphene oxide (PGO) was prepared by using phosphoric acid as functional reagent, and PGO was grafted with poly(L-lactide) (PGO-PLLA) by ring-opening polymerization of L-lactide as monomer under nano-ZnO catalyst. The results of the orthogonal analysis showed the optimum reaction conditions to be as follows: the reaction temperature of 170 degrees C, reaction time of 14 hours, the mass ratio of PGO of 10 wt%, and the mass of nano-ZnO of 1 wt%. PGO-PLLA was characterized by fourier transform infrared spectroscopy, gel permeation chromatography, and X-ray photoelectron spectroscopy, which demonstrated that the PLLA molecular chains were successfully grafted onto the surface of PGO. Poly (lactic acid)/PGO-PLLA nanocomposites (PLA/PGO-PLLA) were prepared by melt intercalation. Mechanical test and fracture scanning electron microscopy showed that PGO-PLLA (0.3 wt%) improved impact strength of PLA by 52.19%, which resulted in ductile fractures surface of PLA/PGO-PLLA. Microcalorimetry and thermal degradation kinetics proved that PGO-PLLA improved the thermal stability of PLA. Polarized optical microscopy and differential scanning calorimetry confirmed that PGO-PLLA increased crystallization rate and spherulite kernel density of PLA, and crystallinity of PLA/PGO-PLLA reached to 22.05%. Rheological behavior proved that PGO-PLLA increased the self-lubricity of PLA. Enzymatic degradation results illustrated that PGO-PLLA had some inhibition for the biodegradability of PLA based nanocomposites.