The effects of wood species, particle size of wood flours and coupling treatment on the mechanical properties of wood plastic composites(WPC) are investigated in this study. Chemical components of wood flour from 3 different wood species were analyzed by the chemical analysis. Wood flours of 40-60 mesh and 80-100 mesh were manufactured from Larix(Larix kaempferi ), Quercus(Quercus accutisima) , and Maackia(Maackia amuresis) . The wood flours were reinforced into polypropylene(PP) by melt compounding and injection molding, then tensile, flexural, and impact strength properties were analyzed. The order of alpha-cellulose content in wood is Quercus(43.6%), Maackia(41.3%) and Larix(36.2%). The order of lignin content in wood is Larix(31.6%), Maackia(24.7%), and Quercus accutisima(24.4%). The content of extractives in wood is in the order of Larix(8.5%), Maackia(4.4%), and Quercus accutisima(3.9%). As the content of alpha-cellulose increases and the lignin and extractives decreases, tensile and flexural strengths of the WPC increase. At the same loading level of wood flours, the smaller particle size(80-100 mesh) of wood flours showed highly improved tensile and flexural strengths, compared to the larger one(40-60 mesh). The impact strength of the WPC was not significantly affected by the wood species, but the wood flours of larger particle size showed better impact strengths.
The addition of maleated polypropylene(MAPP) provided the highly improved tensile, flexural and impact strengths. Morphological analysis shows improved interfacial bonding with MAPP treatment for the composites.
As a result of the water absorption of WPC's follows, after 500, 1000, 1500, 2000, 2500 and 3000 hr water immersion, Quercus and Maackia showed significantly lower water absorption properties compared to Larix. As wood flour loading increases from 10 to 50 wt%, most wood species showed increased water absorption after a given immersion period. Particle size of wood flour proved to have very significant effects on water absorption of the composites. The effect of MAPP was positive in terms of lowering water absorption of the composites. As the treatment level of MAPP increases, the water absorption of the composites decreases. The lowest water absorption was obtained at the lower wood flour loading(Maackia), smaller particle size and by the addition of MAPP. Thickness swelling of the composites shows close dependency on water absorption.