Poly(lactic acid) Toughening through Chain End Engineering

The intrinsic brittleness of poly(lactic acid) (PLA) has hindered its widespread use in many structural applications. Various strategies have been developed to toughen PLA; however, most of the methods lead to a trade-off in strength or modulus. In this study, a chain end engineering strategy was developed to toughen PLA via an industry-friendly melt processing method. Green acids with multifunctional groups, such as 1,2,3,4-butanetetracarboxylic acid (BTCA), were used to modify PLA chain ends/tails via a melt reaction. A remarkable improvement in toughness (16×) was achieved by the addition of a minimal amount of BTCA (0.5%). At the same time, the toughened PLA samples maintained the tensile strength and Young's modulus of neat PLA, suggesting a unique toughening mechanism that is different from the plasticizing effect. Other acid-based modifiers with different numbers of functional groups were also studied in this work. To understand the toughening, we propose a chain end engineering picture that can improve the toughness via a reduction in the number density of chain ends or defects of entanglement and the formation of long-branch topological structures. This study demonstrates a unique and cost-effective strategy for toughening PLA via scalable melt reaction without sacrificing other mechanical properties of PLA, potentially broadening the applications.