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

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 (<0.5, 0.5 < size < 1.0, and 1.0 < size < 2.0 mm). After pretreatment, the solubilization of PLA was increased to 11.5–40.0 % using alkaline dosage and temperature ranging from 50 to 200 g OH^–/kg BP, 60–100 °C, respectively, in a 1–10 h timeframe. The results were statistically proved using a 3D response surface graph, where the pretreatment was more effective for smaller particle sizes. The reduction in particle size also increased the CH₄ production, which was more pronounced at the strong pretreatment (24 % increment vs. 10–15 %). Computed results indicated 44–86 % conversion of pretreated PLA particles to CH₄, supported by Fourier transform infrared spectroscopy analysis, especially focusing on the intensity of –OH bands.