Effects of filler treatments on the mechanical and morphological behavior of PP+wood flour and PP+sisal fiber

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Abstract
Composites were prepared from waste wood flour, sisal fiber and polypropylene (PP). The surface of the filler was modified to enhance the chemical affinity between hydrophilic cellulosic and hydrophobic polymer. The treatments studied were: a) The addition of a coupling agent; b) chemical treatment with NaOH; and c) the addition of functionalized polypropylene (Polybond 3150 and 3200). After treatment, mixtures of PP with 40% and 20% of the filler, wood flour and sisal fiber respectively, were extruded and injection molded. In the case of wood flour, a mixture of two particle sizes (mesh 20 and 40, 50% each) was used, and in the case of sisal, 10 mm long fibers were selected. Results showed that, regardless of the treatment to which the filler was previously submitted, Young’s modulus was always higher for mixtures prepared with wood flour, with values varying between 2839 and 3150 MPa. Whereas for mixtures with sisal fiber, the modulus’ values varied between 1704 and 2220 MPa. Values of breaking strength, elongation at break and impact strength for PP mixtures with treated sisal fiber were always higher than those for mixtures of PP with wood flour. Based on these results, we can conclude that sisal fiber is an organic filler which, due to its mechanical and morphological characteristics, has a reinforcing effect higher than that of wood flour.