Study of the properties of foamed wood flour filled polypropylene and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) using direct extrusion

In this study the effect of foaming using polymeric microspheres on the properties of wood flour filled polypropylene and a biodegradable polymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is presented. Wood flour loadings up to 40% and blowing agent amounts of 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, water absorption and image analysis of the cross-section. On addition of increased amounts of blowing agent, the density reduction in unfilled polymer were found to be higher than with wood flour filled polymer compounds. The tensile modulus, flexural modulus and strength increased up to 30% wood flour loading. Water absorption increased with increased wood flour loading. Addition of increased amounts of blowing agent resulted in reduced mechanical properties and increased water absorption. Image analysis of the cross-sectional area of the extruded strips showed the presence of cells of non-uniform size at 40% wood flour loading and 3% blowing agent level due to the rupture of some polymeric microspheres in the high viscosity medium of the polymer and wood flour.