Rheological behavior and mechanical properties of sawdust/polyethylene composites

We have characterized the melt rheological behavior and the solid tensile properties of sawdust/polyethylene composites prepared in an internal mixer. Various concentrations (from 0 to 60 wt %) and three particle sizes have been tested, in presence of a coupling agent (maleic anhydride grafted polyethylene). In the molten state, for each particle size, a mastercurve of the complex viscosity as function of frequency can be plotted, using a shift factor depending on weight fraction. We show that the shift factors can be described by a Krieger-Dougherty law, leading to a "universal" viscosity law of the Carreau-Yasuda type. In the solid state, the presence of sawdust increases Young modulus in uniaxial elongation, mainly for small size particles, but reduces dramatically deformation at break and tensile strength.