Effects of particle size on the pretreatment efficiency and subsequent biogas potential of polylactic acid

[Display omitted] •The most effective pretreatment condition was 162.5 g OH–/kg BP, 7.75 h, and 90 °C.•The response surface graph showed that pretreatment was more effective at smaller sizes.•The reduction in particle size also increased the CH4 production by 10–24%.•With only 40% PLA solubilization, 91% CH4 production yield was achieved.•FTIR results, particularly changes in –OH bands, support the findings. The fragmentation of bioplastics (BPs) before pretreatment and anaerobic digestion is conducted for higher efficiency; however, based on the literature, the size reduction varies widely. In this study, initially, various combinations of thermal-alkaline pretreatments were applied at different strengths to the polylactic acid (PLA) in three groups (