A novel aryl hydrazide nucleator to effectively promote stereocomplex crystallization in high-molecular-weight poly(L-lactide)/poly(D-lactide) blends

Abstract

Enhancing the interchain CH3⋯OC interactions between poly (l-lactide) (PLLA) and poly (d-lactide) (PDLA) proves effective in promoting stereocomplex (SC) crystallization of high-molecular-weight (HMW) PLLA/PDLA blends and thus endowing SC-type polylactide (PLA) with super physicochemical properties. In this work, a novel aryl hydrazide-type nucleator N,N,N,N′-salicylic tetra(1,2,4,5-benzenetetracarboxylic acid) hydrazide (BAS) with plentiful hydrazide and hydroxyl groups was designed and applied into HMW PLLA/PDLA blends, aiming to enhance the interchain interactions by forming numerous hydrogen bonds with PLA chains. The results indicate that BAS can simultaneously improve the crystallization rate and SC crystallizaion ability of racemic blend. No matter in nonisothermal or isothermal crystallization, the fraction of SC crystallites all exhibits a substantial enhancement as the BAS content increases. More importantly, exclusive SC crystallization with a quite high crystallinity (Xc,SC= 53.0%) is achieved for the ternary blends isothermally crystallized at 160 °C, which is simultaneously accompanied by a extremely fast crystallization rate and high nucleation density. Based on FTIR analysis, the mechanism of BAS facilitated SC crystallization is interpreted to be the largely enhanced enantiomeric interchain attractions derived from the abundant hydrogen bonds between BAS and PLA. We believe this work could provide significant guidance to develop novel efficient SC-type nucleators and fabricate high-performance SC-type PLA materials.