Tailoring the crystallization behavior of poly(L-lactide) with self-assembly-type oxalamide compounds as nucleators: 1. Effect of terminal configuration of the nucleators

The bio-based and biocompostable semi-crystalline poly(L-lactide), PLLA, suffers from slow crystallization rate. Oxalamide compounds are tailor-made as novel self-assembly-type nucleators in this work, which altered significantly the crystallization kinetics of the PLLA. The terminal structures (cyclohexyl, benzyl and phenyl) show strong influence on their self-organization and nucleation efficiency. Their self-organizing temperature sequence (measured via rheology) in the PLLA melt is cyclohexyl > benzyl > phenyl 190 degrees C, while the nucleation activity follows a reverse order. Consequently, the compounds capped with phenyl group exhibit the highest nucleation efficiency. The oxalamide compounds in the PLLA melt showed varied depression in crystallization and dissolution temperatures, demonstrating a designable miscibility. Interestingly, the dissolved oxalamide compounds could organize into shish-like superstructures that subsequently triggered shish-kebab morphology of PLLA crystals free of any flow or shear. With the aid of phenyl-capped oxalamide compound (e.g. 0.75 wt.%), the crystallization of PLLA occurred at 108 degrees C with a crystallinity of 35% even upon fast cooling (20 degrees C/min), while the half-life crystallization time (t(0.5)) was dramatically reduced by 95% in a wide temperate range. In addition, the oxalamide compounds could significantly reduce the PLLA crystal size without modification on crystal form. (C) 2015 Elsevier Ltd. All rights reserved.