Development of wood plastic composite with reduced water absorption

In this work, wood-plastic composites were developed using plastic lumber (recycled high-density polyethylene, or rHDPE) and wood residues (sawdust). First, raw materials were characterized by infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Second, the formulations of rHDPE/sawdust (100/0, 80/20, 60/40, 50/50, 40/60, weight percentage) were mixed manually and processed by extrusion in a twin-screw extruder (TeckTril, DCT model) equipped with ten temperatures zones. The pelletized samples obtained by extrusion were pressed to obtain the films. The WPC films were characterized by density (ASTM D792-13), melt flow index (MFI- ASTM D1238-13), hardness (ASTM D2240–10), SEM, FTIR and water contact angle measurements. The density results were 0.81, 0.87, 0.66, 1.01 and 0.98 g.cm-3 using 0, 20, 40, 50 and 60% sawdust, indicating good fiber-matrix adhesion, confirmed by SEM images. The FTIR spectra showed peaks of rHDPE and sawdust. No chemical interaction occurred between the components after extrusion. The MFI for WPC decreased in relation to the matrix (100/0), but no significant change was observed regardless of the fiber content used. The wettability of the composites’ surface, evaluated by water contact angle measurements, revealed angles close to 90o, which can be considered an positive result, since no coupling agent was used. The absorption water value for composites was less than 3%, a reference value for absorbing MDF panels.