Ten-year field study of wood plastic composites in Santiago, Chile: Biological, mechanical and physical property performance

  • Douglas J. Gardner
  • Alejandro Bozo
Keywords: decay, flexural properties, polypropylene, termites, swelling


Outdoor durability of wood plastic composites is a major focus of research and development efforts toward development of more robust building materials. Exterior exposure of wood plastic composites  can result in weathering, moisture absorption, fungal and termite attack to various levels of severity depending on the composite formulation. Long-term (> 6 years) field exposure studies of wood plastic composites  are lacking in the scientific literature.  It is the overall goal of this paper to report on a ten-year field study of wood plastic composites  performed in Santiago, Chile. The wood plastic composite  formulations were comprised of polypropylene, wood flour, and various additives. Qualitative measurements were made on the stakes each year including the determination of decay and termite ratings on a scale of 1 to 10 as specified in American Wood Preservers’ Association  Standards. Surface weathering or discoloration, surface fungi colonization, presence of mold, and/or lichen was noted. The amount of dimensional change (swelling) of the samples in ground contact was determined. Determination of flexural properties of the control and 10-year exposed wood plastic composite  stakes were conducted. All the wood plastic composite  stake formulations maintained excellent performance ratings after the 10-year field exposure with ratings of 10 for decay and 10 for termites.The wood plastic composites stakes experienced swelling in contact with the soil with the majority of swelling occurring during the first year of exposure. Although the wood plastic composite  stakes did well regarding decay and termite performance, the portion of the stakes exposed above ground exhibited various amounts of weathering, surface fungal colonization, and mold and mildew depending on the formulation. Flexural properties of the wood plastic composite  stakes decreased or were maintained for the 10-year exposure depending on the composite formulation.


ASTM D 6109. D6109-05. Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastic Lumber and Related Products.

AWPA. 1991. E7-90 Standard method of testing wood preservatives by field tests with stakes. AWPA, Woodstock, Md.

BUTYLINA, S.; HYVARINEN, M; KARKI, T. 2012. A study of surface changes of wood-polypropylene composites as the result of exterior weathering. Polymer Degradation and Stability 97(3):337-345.

FABIYI, J.S.; McDONALD, A.G. 2010. Effect of wood species on property and weathering performance of wood plastic composites. Composites Part A: Applied Science and Manufacturing, 41(10):1434-1440.

FABIYI, J.S.; McDONALD, A.G.; WOLCOTT, M. P.; GRIFFITHS, P. R. 2008. Wood plastic composites weathering: Visual appearance and chemical changes. Polymer Degradation and Stability 93(8):1405-1414.

FABIYI, J.S.; McDONALD, A.G. 2014. Degradation of polypropylene in naturally and artificially weathered plastic matrix composites. Maderas. Ciencia y Tecnología 16(3):275-290.

GARDNER, D.J.; HAN, Y; WANG, L. 2015. Curr. Forestry Report: 139. doi:10.1007/s40725-015-0016-6.

GNATOWSKI, M. 2005. Water absorption by wood plastic composites in exterior exposure.In Proceedings of the 8th International Conference on Woodfiber-Plastic Composites (and other natural fibers) (pp. 23-25).

IBACH, R.; SUN, G.; GNATOWSKI, M.; GLAESER, J.; LEUNG, M.; HAIGTH, J. 2016. Exterior Decay of Wood–Plastic Composite Boards: Characterization and Magnetic Resonance Imaging. Forest Products Journal 66(1):4-17.

IBACH, R.E.; GNATOWSKI, M.; SUN, G. 2013. Field and laboratory decay evaluations of wood–plastic composites. Forest Products Journal 63(3):76-87.

IBACH, R.E.; CLEMONS, C.M.; SCHUMANN, R.L. 2007. Wood-plastic composites with reduced moisture: Effects of chemical modification on durability in the laboratory and field. In Proceedings of the 9th International Conference on Wood & BioFiber Plastic Composites, Forest Products Society pp. 259-266.

JMP. 2008.Statistical Discovery Software, Version 8. SAS Institute, Inc., Cary, NC.

KLYOSOV, A.A. 2007. Wood-plastic composites. John Wiley & Sons.

MORRELL, J.J.; STARK, N.M.; PENDLETON, D.E; McDONALD, A.G. 2006. Durability of wood-plastic composites. Wood Design Focus 16(3):7-10.

ROSS, R.J. 2010. Wood handbook : wood as an engineering material. USDA Forest Service, Forest Products Laboratory, General Technical Report FPL- GTR-190, 509 p.

SCHAUWECKER, C.; MORRELL, J. J. ; McDONALD, A. G. ;FABIYI, J. S. 2006. Degradation of a wood-plastic composite exposed under tropical conditions. Forest Products Journal 56(11/12):123-129.

SMITH, T. 2005. Article on the potential for recycling float rope used by lobstermen. Mainebiz 3219. 24 pp. http://digitalcommons.portlandlibrary.com/news_mainebiz/3219/

STARK, N. 2001. Influence of moisture absorption on mechanical properties of wood flour-polypropylene composites. Journal of Thermoplastic Composite Materials, 14(5):421-432.

STARK, N.M.; GARDNER, D.J. 2008. Outdoor durability of wood-polymer composites (pp. 142-165). Woodhead Publishing, Philadelphia.

TASCIOGLU, C.; YOSHIMURA, T; TSUNODA, K. 2013. Biological performance of wood–plastic composites containing zinc borate: Laboratory and 3-year field test results. Composites Part B: Engineering 51:185-190.

XU, K.; FENG, J.; ZHONG, T.; ZHENG, Z.; CHEN, T. 2015. Effects of volatile chemical components of wood species on mould growth susceptibility and termite attack resistance of wood plastic composites. International Biodeterioration & Biodegradation 100:106-115.