Surface tearing and wall slip phenomena in extrusion of highly filled HDPE/wood flour composites

The extrudate surface tearing of highly filled high-density polyethylene (HDPE)/wood flour composites has been investigated in relation to the rheological properties and the wall slip phenomenon in capillary dies. Rotational and capillary rheometers were employed to measure the rheological properties. Mooney analysis was used for determination of wall slip velocity. The results showed considerable increase of storage modulus, dynamic and shear viscosity with increasing wood flour loading. It was also found that all wood filled composites did not obey the Cox-Merz rule. The wall slip velocity depends on wood filler content and shear rate. Generally, with increasing shear rate the slip velocity sharply increases leading to plug-like flow. It was observed that the surface of the extrudates becomes smoother with increase in shear rate and wood flour content.