Crystallization of poly(lactic acid) nucleated with the sorbitol TBPMN
F.F.G. Sebek, Olivier Nguon, A. Bartos, M. ten Brinke, Martin van Drongelen, Hubert Gojżewski, John A. Lefas, G. Julius Vancsó
Abstract
We report on the crystallization of polylactic acid (PLA) films in the presence of a sorbitol-based nucleating agent; 1,2,3-tridesoxy-4,6:5,7-bis-O-[(4-propylphenyl) methylene]-nonitol (TBPMN). Dispersion of the nucleating agent was performed by solution-mixing and melt-blending. Crystallization behavior was studied by differential scanning calorimetry (DSC). The structure and morphology were characterized by wide-angle X-ray scattering (WAXS), optical imaging, and atomic force microscopy (AFM). A significant impact of the nucleating agent was observed at or above a threshold concentration of 2 wt.%, which was assigned to the solubility limit of TBPMN. The degree of crystallinity reached up to 39.6 % with 2 wt.% TBPMN. An influence of the dispersion method was observed on the peak temperature of crystallization (Tcp). While Tcp decreased slightly for solution-mixed films, a sigmoidal trend was noted for melt-blended samples. Under isothermal conditions at 100 °C, the crystallization half-time was lowered from 6.5 min to 1.0 min. Avrami analysis pointed to the formation of 2-dimensional or 3-dimensional crystalline domains; WAXS data revealed α- and δ-crystals, depending on the dispersing method. AFM imaging showed a nanosized fibrillar network of the nucleator within the PLA matrix, demonstrating that TBPMN acted as a soluble self-assembly nucleator.