Effect of filler properties on the modulus of oriented polypropylene filled with flake-like fillers

Flake-like fillers with various particle sizes (talc: 0.8, 3.3, 10.0, 25.5 μm; mica: 15, 32, 98, 320, 730 μm) were mixed with polypropylene (PP). The effect of flake-like filler properties such as filler aspect ratio, filler size, and filler content on the modulus of oriented PP composites was investigated. The relative modulus (Ec d /Er d, where Ec d and Er d are the modulus of oriented PP composites and the modulus of oriented PP, respectively) is shown to be determined by the following factors: (1) orientation factor of the PP matrix, (2) filler properties (filler content, aspect ratio, modulus), and (3) void properties (void volume, void length). The filler size dependence can be clearly recognized, showing an increase in Ec d /Er d as filler size decreased for PP/talc and PP/mica systems. In addition Ec d /Er d is dependent primarily on void volume, irrespective of filler size, aspect ratio, filler content, or orientation of PP matrix for PP filled with flake-like fillers.