The effect of alkali pretreatment on mechanical and morphological properties of tropical wood polymer composites

In this study, mechanical and morphological properties of wood polymer composites (WPCs) from five kinds of selected tropical light hardwoods namely Jelutong (Dyera costulata), Terbulan (Endospermum diadenum), Batai (Paraserianthes moluccana), Rubberwood (Hevea brasiliensis), and Pulai (Alstonia pneumatophora) were investigated. Methyl methacrylate (MMA) and styrene (ST) vinyl monomer mixture (50:50; volume:volume) was used in preparation of WPCs. Before being impregnated with an MMA/ST monomer mixture, wood species were chemically pretreated with 5% sodium hydroxide (NaOH) solution for the reduction of hydrophilic hydroxyl groups and impurities from the cellulose fibre in wood and to increased adhesion and compatibility of wood fibre to polymer matrix. Monomer mixture (MMA/ST) was impregnated into raw wood and NaOH pretreated wood specimens to manufacture wood polymer composite (WPC) and pretreated wood polymer composite (PWPC). Mechanical tests and microstructural analysis were conducted. Comparison has been made among the properties of raw wood, WPC and PWPC. The result reveals that PWPC yielded better mechanical and morphological properties compared to WPC and raw wood.

► We manufactured WPC and PWPC from several kinds of selected tropical light hardwoods.
► NaOH reacts with hydroxyl groups of wood and increased the adhesion and compatibility of wood to polymer.
► Significant improvement of modulus of elasticity and compression strength of PWPC materials.
► Enhanced degree of crystallinity of wood composite was ascribed to the alkali pretreatment.
► PWPC yielded better mechanical and morphological properties compared to WPC and raw wood.