The effect of acrylate modification of wood flour on the structural characteristics and physical behavior of wood flour/polypropylene composite product

Wood plastic composites are produced of mixing thermoplastic polymers with organic, inorganic and natural fillers. The incompatibility of natural fillers with the non-polar polymer matrix results in weak adhesion at the interface of wood fibers with polymer and lack of stress transfer from the polymer to the wood fibers, which leads to a decrease in the mechanical and physical properties of the resulting product. Based on previous researches, in addition to using coupling agents to improve the adhesion between fibers and polymer matrix, modification of natural fillers can also improve the properties of wood-plastic composite products. In this research, the effect of chemical modification of lignocellulosic fillers with glycidyl methacrylate and methyl methacrylate on the functional properties of polypropylene wood plastic composite were investigated. Poplar wood flour was modified with glycidyl methacrylate (GMA) and combination of glycidyl methacrylate/methyl methacrylate (GMA/MMA) under argon gas and the changes in chemical structure, thermal stability and physical properties of control and modified flours were evaluated. Samples of wood plastic composites made using control flour and polypropylene in weight ratios of 80:20, 70:30 and 60:40%, without and with MAPP, and flours modified with glycidyl methacrylate and glycidyl ethacrylate/methyl methacrylate in the same weight ratio of mixing by injection molding method. Physical properties of composites according to ASTM standard D 570 and morphology using field emission scanning electron microscope images was evaluated. Based on the findings of this research, modification with acrylate compounds including: glycidyl methacrylate and methyl methacrylate, by changing the chemical structure, created a significant improvement in thermal stability and physical properties of wood flour. Based on the FTIR results, the chemical changes of wood flour by combined modification of glycidyl methacrylate/methyl methacrylate under benzoyl peroxide were more obvious than the glycidyl methacrylate due to the polymerization of methyl methacrylate. With increase of natural filler ratio, the water absorption of the product increased. The wood flour modification with glycidyl methacrylate as a bifunctional agent improved the adhesion and compatibility of methyl methacrylate polymer with the cell wall of wood flour. The reaction of the cell wall with glycidyl methacrylate reduced the moisture absorption potential of the cell wall by changing the structure of holocellulose and reducing the hydroxyl groups, and the physical properties of the resulting product were improved by increasing the compatibility of the flour with methyl methacrylate and the matrix. In comparing modification of glycidyl methacrylate with glycidyl methacrylate/methyl methacrylate, combined modification by creating a more uniform structure and better compatibility between components, created a more noticeable improvement in physical properties of composite compared to cell wall modification with glycidyl methacrylate, and this effect became more noticeable with increasing filler ratio.