The effect of clay organophilization on wood plastic composite (WPC) based on recycled high density polyethylene (HDPE) and coir fiber

Abstract

One way to optimize composite mechanical properties is through hybridization with small amounts of reinforcing fillers. Thus, this study investigates the effect of incorporation of 3 wt% of clay (BT) and organoclay (OBT) on the properties of a recycled wood plastic composite (WPC) based on HDPE and 20 wt% of coir fiber compounded with 5 wt% of maleic anhydride-grafted polypropylene (PP-g-MA), as coupling agent, and 5 wt% of Struktol TPW 113, as lubricating agent. Raw materials were characterized by X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Coir fiber was characterized by optical microscopy and TGA. Wood plastic formulations (with clay and organoclay) were prepared in an internal mixer coupled to a torque rheometer operating at 190°C, 60 rpm for 10 min. Then, the mixtures were compression molded. Formulations were characterized by SEM, TGA, DSC, tensile and water absorption tests. FTIR analysis showed the characteristic bands of organophilic clay. XRD showed an increment in the interplanar distance of the clay, after the incorporation of quaternary ammonium salt (distearyl dimethyl ammonium chloride, Praepagen® WB), confirming the organoclay formation. Organophilization decreases the clay hydrophilic character and reduces the water uptake of WPC-BT. Despite the fact that BT incorporation led to WPC nanocomposite with intercalated structure, this WPC-clay composition did not show a significant increase in tensile strength and elongation at break. The poor interfacial adhesion between the raw materials and the polymer matrix, the low aspect ratio provided by coir fibers and also, the partially intercalated structure of composites have contributed to this behavior.