In-Process Measurements of Flow Characteristics of Wood Plastic Composites

The flow characteristics of polypropylene filled with high percentages of wood flour (50 and 70 wt%) are investigated at a feasible processing temperature (195 A degrees C). Rotational rheometry in oscillatory mode in conjunction with the Cox-Merz rule is ineffective at this temperature due to insufficient linear viscoelastic region (LVR) size and ease of fibres degradation. An in-line rheometer, directly attached to a single screw extruder, is used to avoid these problems: this method allows measurements in real processing conditions with no LVR issues and with reduced degradation risks. The 70 wt% displays plug flow, thus it has been impossible to obtain the flow curve but only the slip velocity as a function of shear stress. The 50 wt% could be corrected for slip using the Mooney procedure. Comparing the flow curve of this material with the ones of the 30 wt% and the unfilled polypropylene matrix, a single master-curve can be obtained and modelled with a Carreau-Yasuda equation.