Coextruded Polyethylene and Wood-Flour Composite: Effect of Shell Thickness, Wood Loading, and Core Quality

Coextruded recycled polyethylene and wood-flour composites with core–shell structure were manufactured using a pilot-scale coextrusion line. The influence of wood loadings and thickness of the shell layer and core quality on mechanical and water absorption properties of the composites were investigated. Core–shell structured profile can significantly improve flexural and impact strengths of composites especially when a relatively weak core was used. However, the coextruded profile with unreinforced shell may have a reduced modulus when a strong core was used. The shell layer also protected coextruded composites from long-term moisture uptaking, leading to improved dimensional stability compared with the corresponding un-coextruded controls. When the shell thickness was fixed, less wood loading in the shell layer did not cause obvious flexural modulus and dimension change but improved impact strength and water resistance of the coextruded composites. When wood loading in the shell layer was fixed, increased shell thickness improved impact strength but affected modulus negatively. Thickened shell layer helped reduce water uptaking but did not change dimensional stability of coextruded composites remarkably. Overall enhancement of composite strength was more pronounced for the weaker core system. Thus, the coextrusion technology can be used to achieve acceptable composite properties even with a relatively weak core system—offering an approach to use recycled, low quality plastic-fiber blends in the core layer. VC 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: