Rheology for Modeling of Extrusion of Wood Plastic Composites

Extensive rheological studies on the wood plastic composites (WPC) of various wood flour content based on the polypropylene (PP) matrix are presented. Viscous flow properties as well as the slip and yield stress phenomena are discussed. Rheological models of Klein and Ostwald de Waele are used for flow modeling, Navier model is applied for slip description and Bingham model is used for yield stress. Process simulations are performed, using recently developed the global computer model of WPC extrusion, to predict the process parameters (flow rate, pressure, and temperature development, melting rate, etc.), and to study the influence of the WPC material characteristics on the process flow. Simulations are validated experimentally, and are discussed with respect to both rheological and modeling aspects. It is concluded that the location of the extrusion operating point which defines the thermo-mechanical process conditions is fundamentally dependent on the rheological material characteristics, including yield stress and wall slipping.