Analysis of Free Volume Content in Ultra-high Molecular Weight Polyethylene and Polypropylene Blends

The Positron annihilation technique has been applied to study the blends of ultra-high molecular weight polyethylene and polypropylene. A positive deviation of free volume content in the blends has been found compared to the linear addition relationship. The phenomenon means a low density in the interface domain, which leads to the excess of free volume. A free-volume distribution model for incompatible blends was built and the concept of interface free volume was proposed to explain the positive deviation of free volume. The relationship between interface free volume and interface density and scattering phase average size was obtained. The model agrees with the experimental results quite well.