# Alien Wood Species as a Resource for Wood-Plastic Composites
## 3 Results and Discussion  
Most of particles (65-70%) used in experiment was size class 1.5 and lower, as classified by screening (particles that fell through sieve with opening 2.0 mm), while minority of particles (30-35%) was size class 2 mm and higher (Table 3). Although particles were prepared under same conditions, there are differences between them related to the particle size class (share of residue on the sieve). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Size Class**} & **A** & **B** & **C** & \multirow{2}{*}{**D**} & **E** \\  & **Boxelder** & **Horse** & **Tree of** & & **Black Locus** & **Honey** \\  & **Maple** & **Chestnut** & **Heaven** & & **Locust** \\ \hline Dust & 9\% & 6\% & 6\% & 7\% & 7\% \\
0.237 & 11\% & 10\% & 13\% & 12\% & 14\% \\
0.6 & 12\% & 12\% & 13\% & 13\% & 14\% \\
1.0 & 9\% & 9\% & 9\% & 10\% & 9\% \\
1.27 & 9\% & 9\% & 9\% & 8\% & 8\% \\
1.5 & 18\% & 19\% & 17\% & 17\% & 16\% \\
2.0 & 27\% & 30\% & 26\% & 27\% & 27\% \\
4.0 & 5\% & 5\% & 6\%  
The PE matrix (or the matrix of WPC in general) is responsible for the load transfer between constituents and moisture resistance, while wood is responsible for density, strength and stiffness. The result (properties of WPC) should be the combination of the best properties of the components. The impact of the wood species can already be seen in the WPC density (Table 4 and Figure 5), where the densities of WPC boards made of higher density wood species differ from those of lower density and mixture. With regard to the density of the wood species, we can divide the material into two different categories, namely wood species below 0.6 g\(\cdot\)cm\({}^{-3}\), and those with higher density. From this perspective, we can observe an interesting relationship between the density of the wood itself and the density of the WPC (Figure 5). The highest increase in density was at use of the horse chestnut (compaction ratio (Ratio between WPC density and density of wood species) 1.88), while the lowest was in black locust (compaction ratio 1.23), which was also expected. Wood species with low density are indeed more compressible at the same condition as those with higher density. Furthermore, we can observe from Figure 5 that an increase in density results in a decrease in WPC. Again, we can notice two different set namely behaviour of wood species with a density below and those above 0.6 g\(\cdot\)cm\({}^{-3}\). The decrease in density is more pronounced for boards made from wood species with low density, while differences are smaller for boards made from wood species with density above 0.7 g\(\cdot\)cm\({}^{-3}\). Such behaviour could be related to compressibility of wood or to penetration of polymer matrix into cell lumens. Tangential diameter of vessel lumina are: 50-100 \(\upmu\)m in _Acer negundo_, \(\leq\)50-100 \(\upmu\)m in _Aesculus hippocampusatum_, \(\geq\)200 \(\upmu\)m in _Ailanthus altissima_, 100-\(\geq\)200 \(\upmu\)m in _Robinia pseudoacacia_ (with common tyloses) and 100-\(\geq\)200 \(\upmu\)m in _Gleditsia triacanthos_[32]. The polymer compound penetrated easily into larger lumens at more dense wood species, while at wood species with lower density the compression of cell wall occurred prior to mobilization of polymeric compound into cell lumens. For low density wood species, the increase in density is due to the compression of the cell walls, while for high density wood species the penetration of PE in lumens lead to a higher density (although the compression ratio is lower). The differences between alien wood species are less obvious in terms of flexural (Figure 6; \(p\) value 0.40) and tensile strength (Figure 7; \(p\) value 0.06), while the differences in modulus of elasticity (Figure 8; \(p\) value 0.00), sorption properties (Figures 9 and 10; \(p\) value 0.01 respectively 0.00) and dimensional stability (Table 4) are more significant (at \(\upalpha\) = 0.05).