# Alien Wood Species as a Resource for Wood-Plastic Composites
## 2 Materials and Methods  
### WPC Boards Preparation  
We prepared WPC boards using some of the most widespread invasive alien hardwood species present in Slovenia, namely: boxelder maple (_Acer negundo_), horse chestnut (_Aesculus hippcastanum_), tree of heaven (_Ailanthus altissima_), black locust (_Robinia pseudoacacia_) and honey locust (_Gleditsia triacanthos_). The boards were produced using wood of the aforementioned species and polyethylene (PE) powder Dowlex(tm) 2631.10 UE obtained from local company ROTO-Pavlinjek d.o.o. (MURSKA SOBOTA, Slovenia). The physical properties of the powder used are shown in Table 1.  
Maleic anhydride grafted polyethylene (MAPE) was used as a coupling agent (donated by Graft Polymere d.o.o., Ljubljana, Slovenia). MAPE was added to increase the affinity and adhesion between wooden constituents and polymeric matrices. MAPE acts as so-called coupling agent or compatibilizing agent. The polyethylene content was 46.5% and MAPE 3.5%, while 50% of the total mass consisted of wood particles obtained from 5 alien wood species with different densities [17]:  
* black locust (_Robinia pseudoacacia_): density 0.778 g\(\cdot\)cm\({}^{-3}\)
* boxelder maple (_Acer negundo_): density 0.560 g\(\cdot\)cm\({}^{-3}\)
* honey locust (_Gleditsi triacantthos_): density 0.705 g\(\cdot\)cm\({}^{-3}\)
* horse chestnut (_Aesculus hippoastanum_): density 0.495 g\(\cdot\)cm\({}^{-3}\)
* tree of heaven (_Ailanthus altissim_): density 0.555 g\(\cdot\)cm\({}^{-3}\)  
The 50% wood content was selected based on a report by [PERSON] et al., 2012 [27], which showed that the mechanical properties of WPC increased by up to 50%, while a higher share led to a decrease in mechanical properties. A two-step decomposition process was used to break down wood into particles (Figure 1). The breakdown of solid wood into chips was carried out in a Prodeco M-0 chipper, which has an output screen with openings of 25 mm in diameter. The ring chipper used for production of particles was a Condux CSK 350/N1 ring chipper (the gap between the blade and beating bar was 1.25 mm). After chipping particles were analysed by sieving, whereby 100 g of particles were placed on the top sieve. After 10 min of sieving, the residues on each sieve were weighted. The particles used for the experiment are shown in Figure 2.  
As the moisture content of the particles was higher than required for WPC production, the particles were dried at 80 \({}^{\circ}\)C for 24 h to achieve a moisture content below 4% (the actual moisture content for board production was between 0.9% and 2.3%). After drying, the par \begin{table}
\begin{tabular}{c c} \hline \hline
**Physical Property** & **Value** \\ \hline Density & 0.935 g\(\cdot\)cm\({}^{-3}\) \\ Melt index, 190 \({}^{\circ}\)C/2.16 kg & 7 g/10 min \\ Melting point & 124 \({}^{\circ}\)C \\ Vicat softening point A120 & 115 \({}^{\circ}\)C \\ Deflection temperature under load HDT B & 52 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical properties of polyethylene powder DowlexTM 2631.10 UE (values were determined by the supplier). Figure 1: Wood break down process. ticles were mixed by hand with PE powder and MAPE. The mass ratio was 50:46.5:3.5 (wood:PE:MAPE). The prepared mixture was hand formed into a frame measuring 300 \(\times\) 300 mm\({}^{2}\), which was placed on a steel plate. The target thickness was 4 mm, the target density 0.9 g\(\cdot\)cm\({}^{-3}\). Wood-PE mat was flat pressed at 180 \({}^{\circ}\)C for 10 min at a specific pressure of 3 MPa. After 10 min the boards were transferred to the cold press. The specific pressure during cold pressing was the same as during hot pressing (3 MPa), while the pressing temperature was set at 25 \({}^{\circ}\)C (equal to room temperature). The cooling process also hardened the PE. The process for preparing the WPC is shown in Figure 3.  
Six sets of WPC boards were prepared from different wood species as shown in Table 2:  
Figure 3: Schematic layout of wood plastic composites (WPC) preparation.