Process-Related Mechanical Degradation of the Wood Component in High-Wood-Content Wood-Plastic Composites


  • B. Kristoffer Segerholm
  • Stefan Vellekoop
  • Magnus E. P. Wålinder


WPC, particle size, micromorphology, acetylated wood, thermally modified wood, mechanical degradation


Micromorphological studies of wood-plastic composites (WPC) are crucial for deeper understanding of their physical, mechanical, and durability properties. The objective of this study was to examine process-related mechanical degradation of the wood component in an extruded high-wood-content WPC. WPC with ≈70% wood content and three distinctly different ground wood components were manufactured by a conical extrusion technology, ie WPC were prepared with an unmodified, acetylated, or thermally modified wood component. Size and shape of wood components were determined before and after the extrusion process. Micromorphology of WPC samples was studied using a scanning electron microscope (SEM) and a surface preparation technique based on UV laser ablation. This micromachining technique was also applied to prepare thin specimens for micromechanical analysis using a tensile stage mounted in a SEM. Results show that extrusion processes cause a significant mechanical degradation of the wood component. Degradation was most pronounced for the thermally modified wood component, and interestingly, this resulted in a more homogenous WPC micromorphology compared with WPC with unmodified and acetylated wood components. WPC with thermally modified wood also exhibited the highest micromechanical strength.


Anon (2003) ThermoWood handbook. Finnish ThermoWood Association.'> (2011) Wood-plastic composites: Technologies and global markets.'> L-E, Wålinder MEP (2010) Ageing of modified wood. Part 1: Wetting properties of acetylated, furfurylated, and thermally modified wood. Holzforschung 64:295-304.nCarus M, Gahle C (2008) Injection moulding with natural fibres. Reinforced Plastics 52(4):18-22, 24-25.nCaulfield DF, Clemons C, Jacobson RE, Rowell RM (2005) Wood thermoplastic composites. Pages 365-378 in RM Rowell, ed. Handbook of wood chemistry and composites. CRC Press, New York, NY.nGacitua EW, Bahr DF, Wolcott MP (2008) Damage of the cell wall during extrusion and injection molding of wood plastic composites. Paper AP-5 in Proc 51st International Convention of Society of Wood Science and Technology, 10-12 November 2008, Concepción, Chile. Society of Wood Science and Technology, Madison, WI.nHill CAS (2006) Wood modification; Chemical, thermal and other processes. John Wiley & Sons Ltd, West Sussex, UK. 239 pp.nJacobson RE, Caulfield DF, Rowell RM, Sanadi AR (1995) Recent developments in annual growth lignocellulosics as reinforcing fillers in thermoplastics. Pages 1171-1180 in Proc 2nd Biomass Conference of the Americas: Energy, Environment, Agriculture, and Industry, 21-24 August 1995, Portland, OR. National Renewable Energy Laboratory, Golden, CO.nKlyosov AA (2007) Wood-plastic composites. John Wiley & Sons, Inc., Hoboken, NJ. 698 pp.nLarsson Brelid P, Segerholm BK, Westin M, Wålinder MEP (2006) Wood plastic composites from modified wood: Part 1—Conceptual idea, mechanical and physical properties. International Research Group on Wood Preservation, Document No. IRG/WP 06-40338, Stockholm, Sweden.nRowell RM (2006) Acetylation of wood: A journey from analytical technique to commercial reality. Forest Prod J 56(9):4-12.nRowell RM (2007) Challenges in biomass—Thermoplastic composites. Journal of Polymer and the Environment 15(4):229-235.nRowell RM, Ibach RE, McSweeny J, Nilsson T (2009) Understanding decay resistance, dimensional stability and strength changes in heat-treated and acetylated wood. Journal of Wood Material Science and Engineering 4(1-2): 14-22.nRowell RM, Sanadi AR, Caulfield DF, Jacobson RE (1997) Utilization of natural particles in plastic composites: Problems and opportunities. Pages 23-52 in AL Leao, FX Carvalho, and E Frollini, eds. Lignocellulosic-plastics composites. Universidade de Sao Paulo Press, Sao Paulo, Brazil.nRowell RM, Tillman A-M, Simonson R (1986) A simplified procedure for the acetylation of hardwood and softwood flakes for flakeboard production. J Wood Chem Technol 6(3):427-448.nSegerholm BK (2006) Unpublished data. SP, Technical Research Institute of Sweden, Stockholm, Sweden.nSegerholm BK, Omidvar A, Wålinder MEP (2009) Acetylation to minimize water uptake and deformation of high wood content WPC. Pages 239-242 in F Englund, CAS Hill, H Militz, and BK Segerholm, eds. Proc Fourth European Conference on Wood Modification, 27-29 April 2009, Stockholm, Sweden. SP Technical Research Institute of Sweden, EcoBuild, Stockholm, Sweden.nSegerholm BK, Wålinder MEP, Larsson Brelid P, Walkenström P, Westin M (2005) Wood plastic composites made from acetylated wood—Effects on water vapour sorption behaviour and durability. Pages 233-242 in Proc 9th European Panel Products Symposium EPPS, 5-7 October 2005, Llandudno, Wales. The Biocomposite Centre, University of Wales, Bangor, Wales, UK.nSegerholm BK, Walkenström P, Nyström B, Wålinder MEP, Larsson Brelid P (2007) Micromorphology, moisture sorption and mechanical properties of a biocomposite based on acetylated wood and cellulose ester. Journal of Wood Material Science and Engineering 2(3-4):106-117.nSeltman J (1995) Opening the wood structure by UV-irradiation. Holz Roh Werkst 53:225-228.nStamm AJ (1964) Wood and cellulose science. The Ronald Press Company, New York, NY.nStamm AJ, Tarkow H (1947) Dimensional stabilization of wood. J Phys Colloid Chem 51:493-505.nTarkow H, Stamm AJ, Erickson ECO (1946) Acetylated wood. Report No. 1593. USDA For Serv Forest Prod Lab, Madison, WI.nWålinder MEP, Omidvar A, Seltman J, Segerholm BK (2009) Micromorphological studies of modified wood using a surface preparation technique based on ultraviolet laser ablation. Journal of Wood Material Science and Engineering 4(1):46-51.nWestin M, Larsson Brelid P, Edlund M-L, Alfredsen G (2006) Wood plastic composites from modified wood: Part 2—Durability in laboratory decay tests. International Research Group on Wood Protection, Document No. IRG/WP 06-40353, Stockholm, Sweden.n






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