Surface Nucleation of Dispersed Droplets in Double Semicrystalline Immiscible Blends with Different Matrices

Abstract

When a minor semicrystalline phase is dispersed in an immiscible blend with another polymer in the form of isolated droplets, its crystallization behavior is dominated by nucleation. In particular, nucleation can occur in the bulk volume of the phase (homogeneous nucleation), at the surface of possible nucleating foreign impurities, or at the interface with the matrix polymer. Dispersed poly(butene-1) (PB) and polycaprolactone (PCL) droplet phases are employed in various matrices (isotactic polypropylene (iPP), high density polyethylene (HDPE), poly(vinylidene fluoride) (PVDF) and poly(butylene succinate) (PBS)). The effect of matrix self-nucleation on the crystallization of the dispersed droplet phase is then probed. It is shown for all the investigated polymer blends that increasing the matrix crystallization temperature (T-c) via self-nucleation favors droplet nucleation at the interface, leading to a corresponding increase in the droplets'; T-c. Interestingly, distinct nucleation effects are observed when different polymer matrices are compared. The highest nucleating efficiency is displayed by the polymer pairs, which are known to exhibit epitaxial crystallization from previous literature, namely PB/iPP and PCL/HDPE. The order of nucleation efficiency of the other matrices is thought to be linked with the extent of crystallographic matching between the substrate and nucleating crystals.