A study of the properties of foamed wood flour filled polypropylene and extrudate surface tearing using direct extrusion

In this study the effect of foaming using polymeric microspheres on the properties of wood flour filled polypropylene is presented. Wood flour loadings up to 40% and blowing agent amounts of 0.5%, 1%, 2% and 3% were evaluated. Direct extrusion of strips using a co-rotating fully-intermeshing twin screw extruder was done and the resultant strips were tested for density, mechanical properties, image and surface analysis of the extrudate. On addition of wood fibers to the unfilled plastics the density, tensile modulus, flexural modulus and impact resistance increased. The addition of foaming agent decreased the mechanical properties with decrease in density and an increase in impact resistance. The image analysis showed the irregularity in the cell morphology due to open and ruptured cells. When 5% loading of thermoplastic silicone elastomer was used as lubricant for 40% wood filled PP, the extrudate surface tearing was reduced or completely eliminated for both foamed and unfoamed WPC.