Achieving PLA with Excellent Heat Resistance and Transparency via Synergistic Nucleation Effect Assisted by Hydrogen Bonding

Abstract

Typically, specific amide nucleating agents (NAs) that can form nanofibrous networks by self-assembly are vital to achieve poly(l-lactic acid) (PLA) with good heat resistance and transparency. However, the long time required for self-assembly during rapid cooling results in a narrow crystallization window for induced PLA, thus requiring a combination of high annealing temperature and a long annealing time. Herein, a synergistic nucleation strategy was introduced to address this challenge, i.e., adopting hexanedioic,1,6-bis (2-benzoyl hydrazide) (TMC) to induce the self-assembly of a N,N-ethylenebis(12-hydroxystearamide) (EBH) nanofibrous network at higher temperature via hydrogen bonding, then promoting the crystallization of PLA via the nucleating effect of EBH nanofibers. In this way, PLA crystals could be induced earlier during the rapid cooling process, resulting in higher crystallinity and smaller crystals. And driven by this synergistic nucleation effect of TMC and EBH, the annealing time of PLA at 85 °C was greatly shortened to 90 s. The accelerated annealing on PLA effectively increased its heat deflection temperature (HDT) to 96.6 °C, and the formation of refined crystals respectively improved its light transmission at 600 nm from 21% to 70% and impact strength from 3.2 to 7.8 kJ/m². This work would offer a universal approach for accelerating the crystallization rate of NAs for PLA and simultaneously widen the application fields of PLA products.