Preparation and thermo-oxidative degradation of poly(l-lactic acid)/poly(l-lactic acid)-grafted SiO₂ nanocomposites

Poly(l-lactic acid)/poly(l-lactic acid)-grafted SiO₂ nanocomposites were prepared by in situ melt polycondensation, in which “free” poly(l-lactic acid) and poly(l-lactic acid)-grafted SiO₂ nanoparticles were formed simultaneously. The maximum values of grafting ratio and grafting efficiency of poly(l-lactic acid) were up to 37.67% and 26.60%, respectively. In the polycondensation system, SiO₂ content was a critical parameter of getting nanocomposites with uniformly dispersed SiO₂ nanoparticles. At lower SiO₂ content, Mn of grafted poly(l-lactic acid) was close to that of “free” poly(l-lactic acid), and poly(l-lactic acid)-grafted SiO₂ nanoparticles could be well dispersed in poly(l-lactic acid) matrix. While at higher SiO₂ content, Mn of “free” poly(l-lactic acid) and grafted poly(l-lactic acid) decreased seriously, especially GPC curves of “free” poly(l-lactic acid) exhibited two peaks due to the aggregation of SiO₂ nanoparticles during the polycondensation process. The grafting ratio and SiO₂ content exhibited a clear effect on the thermo-oxidative degradation of nanocomposites. The existence of poly(l-lactic acid)-grafted SiO₂ nanoparticles dramatically improved the thermo-oxidative stability of poly(l-lactic acid). Compared with that of pure poly(l-lactic acid), T _g, T _c, and T _m of nanocomposites varied slightly.