Flat-pressed wood plastic composites from community forest wood bark and recycled polypropylene: the effect of pressing temperature on the physical, mechanical, and morphological properties

The article describes a new idea related to the use of wood bark powder as a filler material in the production of wood plastic composites using flat-pressed method, based on its thermal stability and abundant availability, enabling replacing wood powder, which has been widely used. This research aims to study the effect of temperature on the physical, mechanical, and morphological properties of flat-pressed wood plastic composites made from Gmelina arborea bark and recycled polypropylene. A 40:60 mesh (5% moisture content) of G. arborea bark powder was mixed with recycled polypropylene (RPP) pellets with a weight ratio of 40:60 and a maleic anhydride (MAH) modifier as much as 5% of the weight of the RPP was added. Mixing the ingredients is done in a rotating blender for 15 minutes at a speed of 80 rpm until homogeneous. The mixture was heated at 175oC until the RPP pellets were completely melted and then cooled at room temperature. After that, the material mixture was made into powder and filtered, and then moulded in a steel plate mould at temperatures of 160, 165, and 170oC under a pressure of 30 kg/cm2 for 4 minutes with a target density of 1 g/cm3. Physical properties including density, moisture content, water absorption, thickness swelling, and volume shrinkage according to ASTM D570 standard were determined. Mechanical properties, such as modulus of elasticity (MOE) and modulus of rapture (MOR), referring to ASTM D7031 standard, and tensile strength parallel to panel length, referring to ASTM D638 standard, were also evaluated. In addition, composite morphology was also studied using scanning electron microscopy (SEM). The results showed that the increasing of pressing temperature had a significant effect on the improvement of moisture content, water absorption, thickness swelling, volume shrinkage, and MOR. MOR value increased by 34.12% when the pressing temperature increased form 160oC up to 170oC. Our method allows improving the physical and mechanical properties of wood bark plastic composites based on a pressing temperature of 170oC.