Lignin-derived biochar for reinforcing and toughening of Poly(lactic acid): effects of filler modification and reactive plant-based compatibilizer

In this research, black liquor from papermaking factories was applied to prepare a functionalized lignin-derived biochar. The microscopic observations confirmed the porous structure of the biochar. This biochar effectively played the role of both a reinforcing and toughening agent for poly(lactic acid) (PLA). Although the addition of untreated biochar to the PLA matrix adversely affected the mechanical performance, the presence of chemically modified biochar, with functional hydroxyl and carboxyl groups, enhanced all mechanical characteristics, including toughness, stiffness, tensile strength, and ultimate strain, as well as thermal properties. For the PLA/modified biochar system with balanced stiffness and toughness, 33%, 19%, 22%, 17%, and 43% improvements were observed in notched impact resistance, yield strength, stress at break, ultimate strain, and tensile toughness, respectively. While in the case of another modified biochar with the strongest reinforcing effect, about 140% increment in the tensile stress at break of PLA was achieved. This biochar assisted the PLA crystallization process and noticeably increased the crystallinity degree. The functionalization of biochar and the presence of an epoxidized soybean oil (ESO), as a plant-based reactive compatibilizer and chain extender additive, improved the filler dispersion state in the PLA-based biocomposite. By adding modified biochar and ESO to PLA, 80% increase was attained in the impact strength.