Poly(lactic acid) bio-composites containing biochar particles: Effects of fillers and plasticizer on crystallization and thermal properties

Abstract

Biochar has emerged as a filler material for bio-degradable composites with favorable thermal and mechanical properties. Therefore, biochar is used in poly (lactic acid) (PLA) and PLA/thermoplastic starch (TPS) based composites. The crystallization and thermo-analytical properties of these blends with increasing amounts (20 to 50 wt. %) of biochar are investigated. In thermogravimetric analysis, the PLA/char composites’ onset degradation temperature and temperature of maximum weight loss decrease with increasing biochar concentrations (320 °C to 275 °C and 380 °C to 350 °C respectively). Contrastingly, in the PLA/TPS/char composites, the impact of the biochar is shielded by the TPS. The unaltered glass transition demonstrates that biochar does not act as a plasticizer in any of the composites, while TPS does. Biochar acts as a nucleation agent, but hinders further crystal growth at high concentrations, as confirmed by isothermal crystallization and infrared spectroscopy. The TPS smoothens the PLA/biochar interface, leading to an obstructed nucleation effect of biochar, proven by differential scanning calorimetry, infrared spectroscopy and scanning electron microscopy. This work demonstrates the shielding effect TPS has on biochar and can help to further understand and optimize the production and biodegradability of these composites.