Tannic acid-induced crosslinking of epoxidized soybean oil for toughening poly(lactic acid) via dynamic vulcanization

Epoxidized soybean oil (ESO) was incorporated into poly(lactic acid) (PLA) to formulate fully biobased and highly tough ESO/PLA blends by using tannic acid (TA) as a green vulcanizing agent. The crosslinking degree of ESO molecules and the interfacial compatibility between the ESO phase and PLA matrix were thus improved. The properties of the TA-ESO phase and its interfacial adhesion with PLA matrix were tailored by changing the molar ratio of TA to ESO, which significantly influenced the crystallization behavior, mechanical properties, thermal stabilities, and morphologies of the TA-ESO/PLA blends. After the incorporation of 10 wt% TA-ESO (based on the final blend) with a ‒OH groups to epoxy rings molar ratio of 0.8 into PLA system, the elongation at break (242%) and tensile toughness (57.4 MJ/m3) of the resulting PLA blend were 7 and 4 times higher than those of the blend with 10 wt% ESO, respectively. Compared to the 10 wt% ESO/PLA blend, the glass transition temperatures and thermal stabilities of the TA-ESO/PLA blends were slightly enhanced due to the increased crosslinking density of the TA-ESO phase; however, a slightly decreased crystallinity was observed for PLA after the addition of TA into ESO phase.