Hybrid composites of wood flour/kenaf fiber and polypropylene were prepared at a fixed fiber to plastic ratio of 40 : 60 and variable ratios of the two reinforcements namely 40 : 0, 30 : 10, 20 : 20, 10 : 30, and 0 : 40 by weight. Polypropylene was used as the polymer matrix, and 40-80 mesh kenaf fiber and 60-100 mesh wood flour were used as the fiber and the particulate reinforcement, respectively. Maleic anhydride and dicumyl peroxide were also used as the coupling agent and initiator, respectively. Mixing process was carried out in an internal mixer at 1808C at 60 rpm. ASTM D 638 Type I tensile specimens of the composites were produced by injection molding. Static tensile tests were performed to study the mechanical behavior of the hybrid composites. The hybrid effect on the elastic modulus of the composites was also investigated using the rule of hybrid mixtures and Halpin-Tsai equations. The relationship between experimental and predicted values was evaluated and accuracy estimation of the models was performed. The results indicated that while nonhybrid composites of kenaf fiber and wood flour exhibited the highest and lowest modulus values respectively, the moduli of hybrid composites were closely related to the fiber to particle ratio of the reinforcements. Rule of hybrid mixtures equation was able to predict the elastic modulus of the composites better than Halpin-Tsai equation.

In this research wood-plastic composite (WPC) panels were produced from high density polyethylene, MDF, and particle-board waste at 60, 70, and 80 wt% fiber loadings using the dry blend/hot press method. Physical and mechanical properties of the panels were studied and compared with conventional MDF and particle-board panels. The results indicated that the studied properties of the composites were strongly affected by the kind and proportion of the wood fiber and polymer. Maximum values of the flexural modulus of the WPC panels were reached at 70% fiber content. The flexural strength and impact strength of the WPC panels declined when fiber content increased from 60 to 80%. The flexural modulus of the WPC panels was lower than that of the virgin MDF panels but the flexural modulus of the composites with 70% fibers was close to that of particle-board panels. Flexural strength of MDF panels was noticeably higher than those of wood-plastic composites whereas the flexural modulus of particle-board panels was comparable to that of the wood-plastic composites at 80% fiber content. Furthermore, water uptake of wood-plastic samples increased with the increase in fiber content; however, it was relatively low compared with virgin MDF and particle-board panels.