Studies on the Thermal and Mechanical Properties of Foamed Wood-Polymer Composites

Wood flour-polypropylene foamed composites, in ratios of 10:90, 20:80, 30:70, and 40:60 (wt./wt.), were prepared with and without maleic anhydride treatment of wood flour and maleic anhydride-grafted PP (MAgPP). The effects of the amount of wood flour and its treatment on the morphology, the mechanical properties, and the thermal properties of the composites were investigated. Vicat softening temperatures (VST) were recorded as 112.9°C, 103.2°C, and 96.2°C for MAgPP wood flour (MPP), maleic anhydride-treated wood flour (MWF), and untreated wood flour (UWF) (40:60 wt./wt.) foamed composites, respectively. The heat distortion temperatures (HDT) were measured to be 80°C, 76°C, and 58°C for the respective composites. DSC thermograms showed an increase in the crystallinity of MPP and MWF composites with an increase in the ratio of wood flour in the composite, whereas the opposite trend was observed in untreated wood flour. Except for impact strength and flexural strength, Young's modulus, flexural modulus, and hardness all increased with an increase in wood flour content. The micrographs confirmed the foaming. The improvement in the properties of the composites is due to the increment in interfacial bonding between polymer and wood flour, which is caused by the compatibilizers.