Effect of chemical modification of wood flour on long-term water absorption and thickness swelling and morphological study of wood plastic composite

Abstract
Background and objectives: Wood plastic composite that briefly (WPC) are called are a new class of composite materials that in recent years have been the attention of many researchers and a major part of the industry. Given that a major part of the combination of these composites to wood flour constitute, can understand that this composites such as wood are moisture absorbent, so, this research with aim of evaluation the effect of chemical modification of wood flour on long-term water absorption and thickness swelling, humidity coefficient diffusion, thickness swelling rate and morphological study of wood plastic composite was done.
Materials and methods: For this purpose first, wood flour with acetic acid, benzyl chloride and sodium hydroxide was modified separately. For ensure the chemical modification, Fourier transform infrared (FTIR) spectroscopy tests was done. Wood flour to weight ratio of 60% with polypropylene Along with 4 per hundred compound (phc) Maleic anhydride modified polypropylene maple in extruding machine were mixed and test specimens were fabricated by using the injection molding machine. Then long-term water absorption and thickness swelling for 1512 hours according to the ASTM D 7031-04 standard were measured. For morphological study of wood plastic composite from scanning electron microscopy was used. For measurement the reaction of wood flour with chemical materials, weight percentage gain (WPG) were measured on the treated wood flour.
Results: The result showed that long-term water absorption and thickness swelling, humidity coefficient diffusion and thickness swelling rate decreased by chemical modification of wood flour. Result of infrared spectroscopy showed that by chemical modification the peak of the hydroxyl groups decreased and scanning electron microscopy images showed an improving the interface between wood and plastic by chemical modification of wood flour. Also the highest weight percentage gain of wood flour related to benzoylation.
Conclusion: As a principle it can be said that nowadays, chemical modification of wood flour for improvement of interface between two phases wood and plastic an admirable idea seems. Using chemical modification of wood flour can be from one side reduced the radius of irregularly capillary tubes available in wood plastic composite and on the other hand from amount of available hydroxyl groups for creating hydrogen bonds with water molecules decreased. These factors improved physical properties of wood plastic composite, so that water absorption and thickness swelling and so speed of water absorption and thickness swelling in wood plastic composite decreased.
Keywords: Humidity coefficient diffusion, Thickness swelling rate, Infrared spectroscopy, Chemical modification.