Competing crystallization of α- and β-phase induced by β-nucleating agents in microdroplets of isotactic polypropylene

The nucleation efficiency of substrates towards a specific polymer is usually based on empirical methods, which depend on the employed experimental conditions. A more quantitative method to study the efficiency of nucleating agents promoting polypropylene beta-phase is reported here. When a polymer is dispersed into sufficiently small droplets, the overall crystallization kinetics is controlled by nucleation, as growth can be orders of magnitude faster than nucleation. Confinement of polypropylene containing the nucleating agent particles into micro-domains (i.e., droplets) within a polystyrene matrix allows the isolation of the nucleation process and the determination of the surface free energy difference, Delta sigma. This parameter describes the intrinsic nucleation efficiency of a particular nucleating agent. Isothermal crystallization measurements were performed for dispersed polypropylene droplets containing three nucleating agents which catalyze the formation of both alpha- and beta-phase (N,N '-dicyclohexylterephthalamide, quinacridone quinone, and tris-2,3-dimethyl-hexylamide of trimesic acid), and the data were analyzed via a first-order kinetics model. According to the calculated Delta sigma values, the nucleating efficiency scale is DCHT > TATA > QQ for alpha-phase, while DCHT > QQ for beta-phase, in spite of the higher total amount of beta-crystals generated by QQ particles.

Automated summary

A more quantitative method to study the efficiency of nucleating agents promoting polypropylene beta-phase is reported in this study. The findings show that the nucleating efficiency scale for alpha-phase is DCHT > TATA > QQ, while for beta-phase it is DCHT > QQ.