Effect of chain extenders on thermal and mechanical properties of poly(lactic acid) at high processing temperatures: Potential application in PLA/Polyamide 6 blend

Poly(lactic acid) (PLA) is vulnerable to severe thermal degradation when it was processed at high temperature, especially above 200 °C. An undesired molecular weight reduction and weight loss caused by both hydrolysis and depolymerization reactions result in poor mechanical performance of final products. Thus, the aim of this work was to study the effect of chain extenders on the thermal and mechanical properties of PLA processed at high temperatures in a twin screw extruder having four different sets of temperature profiles. Two types of chain extenders, multifunctional epoxide (ECE) and polycarbodiimide (PCD) were used with the constant amount of 0.5 phr. All samples were characterized using GPC, MFI, DSC, TGA, FT-IR tensile and impact tester. The GPC results showed that the molecular weight (Mw) of processed PLA tended to decrease when increasing the processing temperatures and its molecular weight distribution (MWD) shifted towards lower molecular weights whereas Mw of all PLA added chain extenders samples increased and MWD exhibited bimodal distribution and slightly shifted towards higher molecular weight population. The addition of both chain extenders also improved elongation at break and impact strength. For processed PLA samples, these mechanical properties decreased. TGA thermograms of PLA added chain extenders samples showed the increase in onset and deflection temperatures when compared to processed PLA ones. The investigation of PLA based matrix (70%wt of total polymer) was also performed by blending with Polyamide 6 (30%wt of total polymer) with 0.5 phr of ECE or PCD in a twin screw extruder within the temperature profile of 170-250 °C. The blend with chain extenders proved to ease the effect of molecular weight reduction without sacrificing the mechanical properties. Both of PCD and ECE provided the improvement in modulus and tensile strength, especially elongation and impact strength for PLA/PA6/ECE blend. They increased by 92.2% and 65.1% respectively when compared to blend without ECE.