Wood plastic composite(WPC) materials have surfaced as a suitable replacement for treated lumber in residential applications. A need also exists to utilize wood-plastic composites (WPCs) for industrial structural applications such as bridge decking. In this study, twenty-two maple and pine polypropylene (PP) formulations were evaluated to establish a structural material with superior mechanical and physical properties compared to current composite formulations. The materials tested were composed of various quantities of wood flour, PP, talc, coupling agent, and a lubricant. Flexural strength, shear strength, water absorption, thickness swell, and extrusion characteristics were determined for each formulation. Modulus of rupture ranged from 3200 psi to 8800 psi, shear strength varied between 1400 psi to 3400 psi, and modulus of elasticity ranged from 507,000 psi to 870,000 psi. Results indicate that the relative effects of material composition on mechanical and physical properties are similar for both pine and maple wood flour. A comparison between wood flour species indicates that pine exhibits superior water absorption behavior and extrusion quality, but maple demonstrates higher mechanical properties. Overall, a pine formulation with moderate quantities of each material component was selected as the optimum formulation, based on the measured physical and mechanical properties.
Wood-plastic composites (WPCs), defined as a thermoplastics reinforced with wood or other natural fibers, are principally produced from commodity thermoplastics such as polyethylene (PE), polyvinyl chloride (PVC), or polypropylene (PP). Current use of WPC materials includes automotive trim, window frames, roof shingles, and residential decking. Compared to timber, WPCs exhibit greater durability, require less maintenance, absorb less moisture, and provide superior fungal resistances. In addition, the wood filler improves thermal stability in contrast to other polymer composites .
WPC materials for marine application
Industrial structural applications of WPC materials have been limited, but a PVC wood-plastic composite for mulation was successful utilized for a marine structure that required significant structural performance. Benefits exist for using an environmentally-benign material for marine applications, principally in reducing the permitting time and costs currently imposed on treated timber. The bridge industry also recognizes preservative treatment as the greatest hindrance for utilization of timber for bridge construction , reinforcing the motivation for developing structural WPCs. To reach this goal, these materials must resist a variety of structural loads while also maintaining resistance to moisture exposure and fungal decay.
Gaining acceptance for the use of WPCs within the structural design community requires a significant quantity of testing, analysis, and demonstrated use. Mechanical testing of WPCs developed for commercial use has been performed on other polymer types, including PE and PVC (Adcock et al., 2001; Haiar, 2000). The work presented here builds on this previous research with the specific objective of establishing a PPbased WPC formulation that exhibits adequate extrusion characteristics, material properties, and water absorption. Such formulations would improve utilization of this emerging material class for structural applications.