Preparation and Characterization of Polymer-Inorganic Nanocomposites by In Situ Melt Polycondensation of L-Lactic Acid and Surface-Hydroxylated MgO

摘要

Compared with pristine polymers, bionanocomposites derived from biopolymers and inorganic nanoparticles have significantly improved electrical/magnetic properties, mechanical properties, thermal stability, gas barrier properties, and fire retardance. In this study, poly(lactic acid) (PLA) nanocomposites were prepared by in situ melt polycondensation of L-lactic acid with different loading ratios of surface-hydroxylated magnesium oxide (MgO) nanocrystals. Molecular weight, structure, morphology, and thermal properties of the nanocomposites were characterized. PLA-grafted MgO (PLA-g-MgO) was isolated from free PLA for the nanocomposite with 3% MgO via repeated dispersion/centrifugation processes and characterized. The weight-average molecular weight of the PLA-0.01%MgO nanocomposite was 55500, which was 30% higher than that of pure PLA. Discoloration of PLA was obviously depressed in the presence of MgO nanocrystals. Formation of hydrogen bonding between PLA chains and surface —OH groups from MgO was detected by Fourier transform infrared spectroscopy. Morphological images showed uniform dispersion of MgO nanocrystals in the PLA matrix and demonstrated a strong interfacial interaction between the PLA matrix and MgO nanocrystals. PLA-MgO nanocomposites exhibited improved thermal stability compared with pure PLA. Calculations based on thermogravimetric analysis revealed that more than 42.5% PLA was successfully grafted into PLA-g-MgO.