Influence of clay organic modifier on the thermal-stability of PLA based nanocomposites

Poly(lactic acid) (PLA) is a biodegradable aliphatic thermoplastic polyester well known for being a promising alternative to petroleum-based materials since it can be produced from renewable resources. Although this polymer has good properties when compared to other biodegradable polymers, it presents some limitations like poor thermal, mechanical resistance and gas barrier. The incorporation of clay minerals has been used as a way to overcome this problem. The present work aims to investigate the influence of clay organic modifier (Cloisite 30B, Cloisite 15A and Dellite 43B) and amount (3 and 5%) on PLA thermal stability. PLA and PLA nanocomposites were submitted to thermo-oxidative degradation at 140 °C during 120 h. Samples removed along the time were characterized by gel permeation chromatography (GPC), scanning electron microscopy (SEM), X-ray diffraction (XRD), nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). After degradation, even though all samples exhibited a significant decrease of molecular weight, it was smaller for nanocomposites. As a consequence of chain scission an increase in the crystallinity degree was observed for all nanocomposites. Results showed that clay mineral incorporation, mainly D43B enhanced the polymer thermal stability.