Extrusion-based wood fibre-PP composites: Wood powder and pelletized wood fibres - a comparative study

The low-density state of wood fibres represents a feeding challenge when introduced as reinforcements in wood fibre-polymer composites manufactured by extruder-based processing. This challenge has prevented commercial use of wood fibres as reinforcements in various composite applications. In the present work, pelletizing of fluffy wallboard fibres and CTMP fibres into pellets was applied to realize a controlled feeding with loss-in-weight gravimetric equipment. The resulting reinforced composite materials were compared to composites filled with wood powders. The effect of two different coupling agents was furthermore examined, having a span in molecular weight and amount of grafted maleic anhydride. A significant improvement in tensile strength, elongation at break and impact strength was observed for the wood fibre reinforced composites compared to the wood powder-filled composites. These property improvements justifies the efforts of developing new feeding strategies that allow for non-destructive handling and feeding of wood fibres as reinforcements in wood fibre-polymer composites, developed by continuous extruder-based processing.