Recycling of wood plastic composites prepared from poly (vinyl chloride) and wood flour

Abstract

The present study emphasized on closed-loop recycling of wood plastic composite (WPC) prepared from poly (vinyl chloride) and wood flour. The research consisted of two parts. The first part concentrated on re-processing industrial scrap of WPC profiles and its mixture with freshfeed (FF) consisting of PVC filled with wood flour. Different weight ratio of the WPC scrap and its freshfeed pellets was dry blended and re- extruded as recycled-WPC profiles at 0:100, 20:80, 30:70, 40:60, 60:40, 80:20 and 100:0 by using an industrial scale twin screw extruder. It was found that the scrap could be mixed up to 30 wt% without losing in the flexural, tensile, compressive properties, suggesting that the 30:70 was the most appropriate mix ratio. The second part focused on the influences of the number of recycling passes for up to 7 passes. A drop in the mechanical properties was notable at the second pass, and it remained relatively unchanged until the fifth pass. Flexural properties were reduced on the seventh pass of recycling. Estimation of the average molecular weights and the molecular weight distribution of the PVC matrix in the recycled WPC revealed that they remained relatively constant until the fifth pass of recycling, the and the were reduced by 14% and 11% respectively at the fifth pass. Significant decrement of both the and the by 35% and 30% was evident on the seventh pass of recycling. Upon re-processing, molecular chain scission was believed to have occurred as a consequence of the shear stress introduced repeatedly on the PVC melt during each re-processing pass. The impact property was found to remain relatively unchanged. Thermal properties such as glass transition temperature (Tg) and degradation temperature (Td) as well as water absorption behavior were not affected by the recycling process. Rheological results in terms of the fusion torque of the recycled WPC were in agreement with the changes in the molecular weight as aforementioned, the fusion torque was notably lowered at the seventh pass of recycling. The present research revealed that the WPC could be recycled repeatedly up to five passes without critically affecting the mechanical, thermal and physical properties of the recycled WPC.