Wood Flour/Polypropylene Composites: Influence of Maleated Polypropylene and Process and Composition Variables on Mechanical Properties

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Abstract
The mechanical properties of wood flour/polypropylene composites may be improved by using coupling agents to enhance the bonding between filler and matrix. We used a two-level, full-factorial experiment to examine the effectiveness of a commercially available additive, Epolene E-43, on strength (tensile, flexural, and cantilever-beam), modulus, impact energy, density, and melt viscosity of composites. The effect of Epolene E-43 was studied alone and in combination with three other variables: the weight ratio of wood flour to total polymer in the composites (45/55 or 55/45), size of wood flour particles (nominal 20 or 40 mesh), and extruder residence time (one or three extrusions). Of all the variables, Epolene E-43 had the greatest effect on strength. This effect was somewhat enhanced by using the 40-mesh wood flour and three extrusions; for this combination of variables, Epolene E-43 caused a 30 percent increase in strength. The combination of Epolene E-43 with a 55/45 wood flour/polymer ratio and 40-mesh wood flour resulted in the largest values of flexural and cantilever-beam modulus. Addition of Epolene E-43 slightly decreased notched impact energy but possibly increased unnotched impact energy. None of the variables had a significant effect on melt viscosity. Average wood flour particle size was decreased by processing, particularly in the presence of Epolene E-43. Overall, these findings indicate that Epolene E-43 exerts some degree of coupling action, which results in improvements in mechanical properties that have practical value. The higher cost of Epolene E-43 can be compensated by increasing the ratio of wood flour to polypropylene.

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