Influence of biochar on the physico-mechanical properties and biodegradation of PLA films

This study investigated how pyrolysis temperature and walnut-shell biochar content affect the structural, thermal and biodegradation behaviour of polylactic acid (PLA) films. Biochars produced at 400 and 700 °C were incorporated at 2 and 10 wt.%. Increasing pyrolysis temperature transformed biochar from hydrophobic to hydrophilic, increased its specific surface area from 2.1 to 356 m² g⁻¹ and pore volume by 395%, and decreased its water contact angle by 16%. These pyrolysis-dependent changes altered particle–matrix contact and PLA structural ordering. At 10 wt.% loading, low-temperature biochar increased initial crystallinity to 8.0%, whereas high-temperature biochar reduced it to 2.0% and caused the largest reduction in thermal stability. Under thermophilic composting, low-temperature biochar at 2 wt.% yielded the highest biodegradation degree (77.2% after 16 weeks), whereas at 10 wt.% it produced the slowest response. At this higher loading, films containing high-temperature biochar biodegraded faster than those containing low-temperature biochar. The results demonstrate that the effect of biochar on PLA biodegradation depends on the interaction between pyrolysis temperature and filler content, mediated by wettability, pore structure, particle–matrix contact and PLA structural ordering.