Study of the thermal stabilization mechanism of biodegradable poly( L ‐lactide)/silica nanocomposites

Biodegradable poly(L‐lactide) (PLA)/silica (SiO2) nanocomposites were prepared by melt compounding to investigate the effect of spherical nanofillers on the thermal stability of PLA. The nanocomposites displayed improved thermal stability both under nitrogen and in air. The stabilization mechanism was attributed mainly to the barrier effect of the network formed, which was demonstrated by the improved barrier properties and rheological performance. The dispersion of nanofiller and matrix‐nanoparticle interactions were investigated to evaluate the dependence of the network on SiO2 loadings. Fourier transform infrared spectroscopy and thermogravimetric analysis indicated that hydroxyl groups on SiO2 surfaces and PLA chain‐ends reacted during melt processing. The resulting grafted SiO2 and entangled PLA chains formed a dense network, which hindered the diffusion of oxygen and volatile decomposition products. Furthermore, the improvement in thermal stability resulted from the restraining effect on the mobility of active hydroxyl end‐groups, so that some related thermal decomposition reactions were inhibited, which was confirmed from gel permeation chromatography measurements.