Effects of Diisocyanate and Polymeric Epoxidized Chain Extenders on the Properties of Recycled Poly(Lactic Acid)

Abstract

Increasing demand in the use of poly(lactic acid) (PLA) leads to a debate about using potential foodstuffs for plastic production and a moral issue when starvation problem is taken into account. One of the solutions is recycling of PLA; however, recycling results in property losses during melt processing due to low thermal stability of PLA. This study focuses on using chain extenders to offset thermal degradation of recycled PLA. The effects of a diisocyanate and a polymeric epoxidized chain extender on the properties of the recycled poly(lactic acid) were investigated. In order to mimic the recycling process, PLA was subjected to thermo-mechanical degradation using a laboratory scale compounder. Chain extender type, loading and mixing time were investigated. On-line rheology and intrinsic viscosity measurements of PLA before and after chain extension confirmed that the molecular weight increased. Dynamic mechanical analysis, rheology and tensile tests revealed that the chain extenders led to a significant increase in modulus, strength and melt-viscosity. It was found that diisocyanate had slightly higher and faster chain extension reactivity than polymeric extender. Differential scanning calorimetry results showed an increase in the crystallization temperature due to the branched and extended chain structure.