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

• Published in: European polymer journal 2015-09, Vol.70, p.400-411
• Main Authors: Ma, Piming, Xu, Yunsheng, Shen, Tianfeng, Dong, Weifu, Chen, Mingqing, Lemstra, Piet J.
• Format: Article
• Language: English
• Subjects: Cooling; Crystallization; Crystallization kinetics; Crystals; Dissolution; Nucleation; Oxalamide compounds; Phenyls; Poly(L-lactide); Shear; Terminals
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2015.07.040

[Display omitted] •Oxalamide compounds (NAs) are tailor-made as novel effective nucleators for PLLA.•The end structure affects thermal behavior and nucleation efficiency of the NAs.•The oxalamide compounds triggered “shish-kebab” morphology of PLLA crystals.•The crystallization kinetics of PLLA was enhanced by the oxalamide compounds. 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°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. 0.75wt.%), the crystallization of PLLA occurred at 108°C with a crystallinity of 35% even upon fast cooling (20°C/min), while the half-life crystallization time (t0.5) 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.