EXTRUSION OF HEAVILY FILLED POLYMERS FOR PRODUCTION OF PLASTIC LUMBER
John Vlachopoulos, David Strutt
McMaster University
CANADA

Keywords: extrusion, fillers, profiles

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HDPE,PVC and other thermoplastics heavily filled with cellulosic fibers (usually up to 60%), are extruded for the production of profiles commonly referred to as plastic lumber or plastic wood.Several patented processes have been developed during the last ten years or so.Frequently, the polymers are obtained from recycling.The patents do not address several important questions relating to rheology and certain defects that usually accompany such extrusions. The present work involves a rheological investigation of the phenomenon of surface tearing that appears like an exaggerated sharkskin in the extrusion of profiles as well some computer simulations.Viscosity,dynamic moduli and extrudate swell have been measured for different filler concentrations.Computer simulations and comparisons with experiments have been carried out. The results offer new insights into the process of plastic lumber extrusion for output enhancement and product property impovement.It appears that either die lubrication or die land cooling is necessary to avoid surface tearing. Some profile designs are more prone to surface defects.Some of the claims of the patent literature are reexamined in the light of the present findings.