# Alien Wood Species as a Resource for Wood-Plastic Composites
## 1 Introduction  
The properties of wood-based composites are determined by the components used for their production. This is also demonstrated in the case of wood plastic composites (WPC), where wood can act as a reinforcement or as a filler and in some cases both. Wood and the derived components are an important factor influencing the properties of wood-based panels [1; 2; 3; 4; 5]. WPC is basically composed of two main components, namely plastic or polymer and wood, resulting in a material which combines the best properties of both components. Although the wood constituents in WPC are small (usually size class between 0.1 mm and 1.0 mm), and (according to [6; 7]) the wood species related differences should be smaller, several authors [8; 9; 10; 11; 12; 13] have shown that the wood constituents (in terms of species and size of constituents) influence the properties of WPC. The influence of the wood species used for WPC depends on the size of constituent obtained during breakdown process (particularly in terms of slenderness ratio), its affinity towards polymeric compound and strength of bond between wooden constituent and polymeric matrices. [PERSON] et al. [14] determined that chemical composition of wood also influences the properties of WPC; namely, they proved that a higher cellulose and lignin content results in better mechanicalproperties but also in lower moisture resistance when the cellulose content is high. One of the disadvantages of using wood in WPC is the reaction of the wood to UV radiation. The effect of UV radiation (e.g., sunlight) on the wood surface leads to photochemical degradation of wood and thus of WPC. Colour changes (darkening) also occur during the production of WPC. Exposure to elevated temperatures during the pressing process leads to the evaporation of extractives, which darken the wood surface and thus also WPC [10; 15]. Based on data from the existing Flora of Slovenia (CCFF) Database, the species _Robinia pseudoacacia_ (black locust) is the invasive alien plant species with the potentially most negative impact on biodiversity. Tree of heaven (_Ailanthus altissima_) and boxelder maple (_Acer negundo_ L.) can also be classified as invasive alien plants with a high negative impact on biodiversity. It is, therefore, undoubtedly useful to raise awareness of the impact of invasive alien plant species on our environment and to look for the most versatile applications, including their use as WPC components. Our main objective is to test the suitability of the most widespread invasive alien hardwood species present in Slovenia for the production of WPC and to encourage their removal from native natural ecosystems by transforming them into a source of raw materials that could be processed into useful products. The mechanical properties of these wood species are not well known, and further information about them may encourage the use of these woods in the most appropriate way in new products. Wood anatomical analyses and machining tests have already been carried out on the same wood species, which overall showed good degree of machinability [16; 17]. In light of the results obtained so far, we believe that the selected wood species may be suitable for the production of WPC due to its anatomical structure and mechanical properties. To verify their suitability for this application, we carried out classical mechanical tests, such as flexural and tensile strength tests. In addition, we performed microstructural analyses of the surface and internal structure of WPC boards using scanning electron microscopy (SEM). SEM is a powerful tool for examining the surface and structure of wood. The application of SEM in wood science is well described in the literature [18; 19; 20; 21; 22]. Recently SEM has been successfully used to study the morphology and surface evaluation of WPC [13; 23]. SEM has been used to evaluate the adhesion between wood and polymer matrix and detect the occurrence of fibre pull outs and voids within the composite [24; 25].