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Different wood species can be expected to affect the properties of wood—polymer composites (WPCs) differently, as they have different chemical compositions. The chemical composition (cellulose, lignin, hot water, and ethanol/ cyclohexane extractive contents) of acacia, eucalyptus, pine, and oak and the morphological properties such as wood fiber length distribution were determined in order to investigate this effect. Composites of linear low-density polyethylene and 10 wt% of each of the wood species were prepared, using polyvinyl alcohol-co-ethylene as a compatibilizer. Significant differences were found between the wood species in terms of both chemical composition and wood fiber length distribution. These affected the properties of the WPCs in different ways. Use of acacia resulted in a WPC with superior mechanical properties and thermal stability compared with the other species, due to its higher cellulose and lignin contents and a favorable wood fiber length distribution; however, acacia composites also showed a higher water absorption rate due to the higher cellulose content. We also found that WPCs containing wood species with a high lignin and extractive content, such as acacia and oak, had a higher resistance to UV degradation.

Hot water extractives, solvent extractives and both hot water and solvent extractives were eliminated from different wood species via Soxhlet extraction. Different wood-linear low density polyethylene (LLDPE) composites were prepared using 10% wood and 7% poly(ethylene-co-vinyl alcohol) as a compatibilizer. A comparison of the mechanical properties, water absorption behaviour and resistance to UV radiation between composites filled with unextracted wood and composites filled with the same species but without the above extractives were carried out. The results illustrated that there are several distinct benefits and drawbacks when using wood without extractives as a filler. Unextracted wood produced composites with better mechanical properties and resistance to UV radiation, while extracted wood led to composites with lower water absorption rates. Using wood without both hot water and solvent extractives as a filler caused the largest reduction in mechanical properties, UV resistance and water absorption rate, compared to composites made with wood where only one extractive component was removed.

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