Control of thermal degradation of polylactide (PLA)-clay nanocomposites using chain extenders

Abstract

The control of thermal degradation of polylactide (PLA) during processing is still a challenge for the industry. In addition, the presence of an organically modified clay intensifies the rate of PLA degradation and molecular weight (MW) reduction. In this work, three different chain extenders: polycarbodiimide (PCDI), tris (nonyl phenyl) phosphite (TNPP) and Joncryl® ADR 4368, were incorporated into PLA and PLA-based nanocomposites containing 2 wt% clay (Cloisite® 30B) in an effort to control thermal degradation. The thermal and rheological properties of the PLA and PLA nanocomposites with and without chain extender were investigated. Thermogravimetric analysis showed an increase in the onset temperature for thermal degradation after the incorporation of PCDI (2 wt%), TNPP (1 wt%), or Joncryl (1 wt%) into the nanocomposite. The rheological results revealed that the addition of such a concentration of chain extender had a profound effect on the degradation and even increased the molecular weight in some cases. The mechanism of stabilization is most likely chain extension that results in the formation of longer linear chains in the PCDI and TNPP-modified nanocomposites, and a long chain branched (LCB) structure in Joncryl-based nanocomposites. It was found that Joncryl was the most efficient chain extender among the ones used in this study.