Polypropylene/metallocene ethylene-octene copolymer blends with a bimodal particle size distribution: Mechanical properties and their controlling factors

Blends of polypropylene homopolymer (PP) and metallocene produced ethylene-octene copolymer (EOR) with a bimodal particle size distribution were investigated. The aim of the work was to study the influences of EOR characteristics and its concentration on the tensile and impact properties of the blends. The matrix ligament thickness between rubber particles was measured and compared to those predicted using the theoretical models. The relationships between blend morphology and impact property were reported. It was found that the content of comonomer and molecular weight of the EOR as well as its concentration in the blends were the major factors controlling the tensile and impact properties of the blends. These factors became ineffective to impact property when the ligament thickness of the matrix was larger than the critical value (T ∼0.3-0.4 μm). To achieve blends of high impact strength, the ligament thickness between rubber particles should be smaller than the critical value, and for a certain ligament thickness, EOR with high octene content and high molecular weight was preferred.