Diisocyanate-Induced Dynamic Vulcanization of Difunctional Fatty Acids toward Mechanically Robust PLA Blends with Enhanced Luminescence Emission

The toughening of poly(lactic acid) (PLA) often involves the use of nonbiodegradable or petrochemical elastomers owing to the lack of effective renewable alternatives and facile routes to tailor desirable morphologies. In this work, we developed a facile and universal dynamic vulcanization strategy of dual monomers to fabricate mechanically robust PLA blends. By increasing NCO/COOH equivalent ratios between l-lysine diisocyanate (LDI) and hydrogenated dimer acid (HDA) (i.e., n(NCO,LDI)/n(COOH,HDA)) above 1.0:1, the phase structure of the resulting PLA blends transformed from the common sea-island morphology to partially or fully co-continuous ones. The extraordinary impact toughness (the maximum impact strength up to 109.8 kJ m(-2)) in combination with the balanced strength and stiffness was attributed to a continuous biopolyamide elastomer (HDAPA) with the simultaneous improvement in both the cross-linking level and interfacial compatibilization. Atomic force microscopy (AFM)-based nanomechanical mapping results suggested that the cross-linking of HDAPA domains gradually prevailed from the boundaries into the whole domains with the elevated n(NCO,LDI)/n(COOH,HDA) ratios. The mechanisms regarding multiple reactions and co-continuity development at an ultralow concentration of the minor HDAPA phase were elucidated. Intriguingly, the enhanced clustering-triggered emission was observed for the PLA/HDAPA blends with a fully co-continuous structure.

Automated summary

In this study, a facile and universal dynamic vulcanization strategy was developed to fabricate mechanically robust PLA blends. By adjusting the ratio of two monomers, the phase structure of PLA blends can be transformed and achieve extraordinary impact toughness.