Repeated mechanical recycling of biodegradable polymers: PLA exhibits less deterioration than PBAT/PLA blend

Abstract

Biodegradable polymers have been extensively researched as alternatives to non-biodegradable fossil-based polymers. Although they reduce environmental impact, their production competes with land needed for food crops. Therefore, exploring their reuse and recycling is essential for enhancing their circular economy and sustainability. This study evaluated the recyclability of commercially available biodegradable polymers, poly (lactic acid) (PLA) and its blend with poly (butylene adipate co-terephthalate) (PBAT), across three cycles of mechanical recycling. Each cycle simulates plastic production, shelf-life, washing, and reprocessing stages. Samples were analysed after molding, ageing, and washing for each cycle using Differential Scanning Calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), tensile testing, and rheological analysis to track changes in crystallization, chemical structure, viscosity, and mechanical behaviors. Results indicated that both PLA and PBAT/PLA (55/45 wt%) blend showed a rise in crystallinity ($X_c$) due to the annealing effect of the ageing and washing. No changes in FTIR spectra and $X_c$ were detected after one recycling cycle, indicating stability. After three reprocessing cycles, second heating crystallinity rose from 2 % to 13 % for PLA and from 2 % to 12 % for PBAT/PLA (45 wt% PLA), indicating morphological changes from degradation and molecular weight reduction. Despite higher crystallinity and a more moderate decline in complex viscosity and storage modulus than PLA, PBAT/PLA showed reduced mechanical properties, with a 90 % drop in elongation at break and nearly 50 % in stress at break, highlighting the need for interventions to control PBAT degradation. PLA maintained strong mechanical properties, demonstrating its potential as a compostable recyclable material.