Direct Reactive Extrusion of PLA in the Presence of a Multifunctional Chain Extender

Abstract

The environmental impact of non-renewable, fossil fuel-based polymers has led to growing interest in sustainable alternatives such as Poly(lactic acid) (PLA). PLA is biodegradable and suitable for packaging application, however due to limited number of efforts to effectively recycle PLAs, its disposal still contributes to the plastic pollution problem. In general, plastic recycling methods could be categorized into three main groups: (i) incineration for energy generation, (ii) chemical recycling, and (iii) mechanical recycling. Among those strategies, mechanical recycling would be the optimal choice due to its applicability to current plastic production lines. However, limited thermal stability of PLA during melt mixing make its mechanical recycling challenging. This study explores the direct use of ketene-based chain extenders in the melt mixing step without any pre-treatments to enhance PLA's properties during thermal recycling. Those ketene-based chain extenders could increase the molecular weight and hence melt viscosity of PLA by reacting its hydroxyl and carboxylic acid end groups. For this purpose, copolymers of styrene, methyl methacrylate and 2,2,5-trimethyl-5-(4-vinylbenzyl)-1,3-dioxane-4,6-dione (MA) were synthesized and directly melt mixed with PLA in micro compounder at 210 °C for 3 mins. Force values were monitored simultaneously through this mixing step. Final molecular weights and thermal properties of PLAs were also analyzed through GPC and DSC analyses.