The Critical Role of Diisocyanate Structure in Toughening PLA via Dynamic Vulcanization of Hydrogenated Dimer Acid

Previous works have demonstrated that diisocyanate-induced dynamic vulcanization of difunctional fatty acid is an effective and promising strategy to highly toughen PLA. However, the effect of diisocyanate structure on the toughening of PLA remains unclear. For this sake, three diisocyanates with different molecular structures, that is, hexamethylene diisocyanate (HDI), 4,4-diphenylmethane diisocyanate (MDI), and dicyclohexylmethane 4,4′-diisocyanate (HMDI), were chosen to induce dynamic vulcanization of hydrogenated dimer acid (HDA) in the presence of PLA. The reaction rates of the diisocyanates with HDA were found to follow the following order: HDI > MDI > HMDI. The higher reactivity of diisocyanates resulted in better interfacial compatibility between the in situ formed polyamide elastomer and PLA components. PLA blends utilizing MDI or HMDI with cyclic structural units have superior tensile strength (TS) and tensile modulus (TM) but minimal improvement in tensile ductility. Among the three PLA blends, the PLA/(HDA + HDI) blend exhibited a bi-continuous morphology and the highest toughness, with an elongation at break of 283.4% and a notched impact strength of 80.1 kJ/m 2 . This work would offer guidance for the development of high-performance PLA blends prepared by dynamic vulcanization of reactive monomers.