UHMWPE-assisted melt strength enhancement of recycled PLA for lightweight foaming

Abstract

Increased utilization of biodegradable polymers to achieve sustainability and decrease the carbon footprint is connected with a necessity to find an effective way of their reutilization. Polylactic acid (PLA), and generally all biodegradable polymers, undergoes significant degradation during reprocessing cycles, leading to inferior products when compared with the original material. Here, ultrahigh molecular weight polyethylene (UHMWPE) was incorporated as a reinforcing phase to create a polymer-polymer composite capable of restoring and enhancing the melt strength of recycled PLA. While recycled PLA lost melt strength during reprocessing, limiting its foamability, the UHMWPE/PLA composites exhibited up to a 5.3-fold increase in melt strength, enabling stable cell growth and expansion during foaming. The composite foams also showed a substantial reduction in thermal conductivity to 0.019 W m-1 K-1 and a lower density of 0.217 g cm-3. These improvements originate from the unique combination of UHMWPE/PLA composite and filler morphology within the PLA matrix, which reinforces the PLA melt and suppresses cell coalescence. The approach under discussion relies on standard blending and foaming techniques, thus offering a simple and scalable route for the conversion of reprocessed and recycled PLA into high-performance, highly expanded foams. These foams can be used for thermal insulation, protective packaging and lightweight structural applications.