Effect of processing conditions on the microstructure of microcellular PP/WF composites prepared by the continuous extrusion molding technology

Abstract

The polypropylene (PP) and wood flour (WF) were mixed first and then extruded by a single-screw extruder foaming system to prepare the microcellular wood-polymer composites (WPCs) in this article. In addition to PP and WF, polyolefin elastomer (POE), talc powders and other fillers were also added to improve the cell structures of the samples. And two types of PP resins were introduced to the formulation of the composites to study the effect of the molecular chain structure on the rheological properties of the samples. Besides, the effects of processing conditions, such as die temperature and screw speed, on the properties of the samples were also investigated. The experimental results indicate that compared with PP1, the complex viscosity of PP2 decreased faster with the shear rate because of the linear molecular chain structure. Besides, the maximum impact strength of PP2/WF composites was 138.5 % higher than that of PP1/WF composites, while the tensile and flexural strength of PP2/WF composites were much lower. In addition, the best microcellular structure and the maximum impact strength were also obtained with the die temperature of 190 °C and the screw speed of 2 rpm.