Crystallization behavior of poly(lactic acid) nucleated by benzoylhydrazide compounds with different methylene...

Poly(lactic acid) (PLA) is an important biobased biodegradable plastics but its inherent crystallization rate is slow. Organic self-assembly nucleating agents have shown excellent nucleating effect in enhancing PLA crystallization. However, the relationship between the chemical structures of organic nucleating agents and their nucleating ability is still not yet well elucidated. Herein, the effect of tramethylenedicarboxylic dibenzoylhydrazide (TMBH) and octamethylenedicarboxylic dibenzoylhydrazide (OMBH) ranging from 0.1 wt% to 2.0 wt% on PLA crystallization was compared. The crystallization temperature (T_p) of PLA shows a bell-shaped relationship with the concentration of TMBH and the highest T_p is reached at 0.25 wt% of TMBH; while the T_p of PLA increases with increasing OMBH concentration until 1 wt% and a slight decrease is observed at 2 wt% of OMBH. The nucleation ability is the best for TMBH at 0.25 wt% loading. The crystalline morphologies were characterized by combining optical and atomic force microscopies, and correlated with the solubility of nucleating agent in PLA. The crystallization mechanism was probed by time-resolved Fourier transform infrared spectroscopy. More importantly, PLA/TMBH blends achieve good balance between heat resistance and transparency at 0.25 wt% of TMBH. It can be concluded that TMBH is better than OMBH in promoting PLA crystallization.