Companies including Conenor Ltd, KS Laatuenergia Ltd and Tiihonen Ismo and VTT Technical Research Centre of Finland Ltd have joined forces in the European H2020 project “HISER” to produce high-quality wood-plastic composites (WPC) from construction and demolition (C&D) wood waste.
The C&D wood waste (Figure 1) is sorted into four different categories according to origin and purity: clean wood fraction, painted wood fraction, plywood fraction and particle/fibre board fraction. The C&D wood fractions are first broken down to components with pre-crushers and cleaned with magnetic and air separators. Still down-sizing the particle size, the wood components are pre-refined by disc refiner. The final refining of wood components is done by hammer mill and the particle size is homogenized by various size screens (Figure 2).
The C&D wood waste downsized into fibres contains 15-20% of moisture which needs to be removed. Drying of the fibres is done simultaneously while preparing the agglomerated extrusion formulations in a high intensity mixer. Other materials used in the formulation, in addition to the dry C&D wood waste (63%) and polypropylene plastic (PP 25%), compose of mineral filler (talc 5%), coupling agent (MAH 2%) and processing aid (wax 5%). The formulations are extruded into 1m long hollow test bars in size 60×40 mm with 8 mm wall thickness using a conical rotary Conex-extruder CWE 380-1.
Examples of measured flexural strengths and elastic moduli of extruded WPCs containing virgin PP are shown in Figures 4 and 5. The best flexural strength is achieved with plywood fraction and the highest elastic modulus is achieved with painted wood fraction. It seems that the particle/fibre board fraction gives the lowest mechanical values in both cases. Generally speaking, the flexural strength of the produced WPCs is at good level and the elastic modulus is at excellent level compared to commonly used WPCs in decking applications in the European markets .
For a complete evaluation, also other important properties of the WPCs like water absorption, dimensional stability and creep will be evaluated from the produced WPCs. All results are benchmarked against the values of commercial WPCs. WPCs based on plastics like polyethylene (PE) and recycled PP and PE from consumer waste (bottles) will be also produced and tested for comparison. Following the material evaluation, the project will focus on new WPC-product development utilizing C&D wood waste and the new WPC products will be validated in the field demonstrations.
 Irmgard Bergmann, Benchmarking performance of European WPC decking, Wood-Plastic Composites 2008, 14-16 October 2008, Vienna.