Stepwise behavior of surface properties caused by phase inversion in a polymer blend filled with dispersed iron

Abstract

The surface properties, mechanical characteristics, and morphology of the PP/CPA-Fe composite based on a polymer blend of polypropylene (PP) and copolyamide (CPA) filled with dispersed iron (Fe) were studied. The effect of stepwise behavior of the surface energy and its dispersive and polar components was previously unknown and discovered for the first time when the composition of the polymer blend was varied in the entire composition range. The surface parameters were found by measuring the contact angle of the testing liquids (water and diiodomethane) and using Owens and Wendt’s approach. Stepwise behavior of the surface energy was caused by the morphology of the composite. The largest change in the surface parameters occurs in the phase inversion region, where the phases of PP and CPA-Fe are co-continuous. Below (for the structure of PP matrix with the inclusions of CPA-Fe) and above (for the structure of CPA-Fe matrix with the inclusions of PP) this interval, changes in the surface energy are minor. In the phase inversion region, the relative contributions of the polar and dispersive parts to the total surface energy were changed from 1 to 14% and from 99 to 86%, respectively that was caused by the interface interaction of the components of the blend. On the contrary, the values of elastic modulus (E) remain constant in the phase inversion region, while the largest changes occur below and above this region.