Stress Relaxation of Wood Flour/Polypropylene Composites at Room Temperature


  • Yi Wang
  • Jinzhen Cao
  • Lizhi Zhu


Wood flour/polypropylene composite, wood flour content, coupling agent, stress relaxation


To investigate the time-dependent property of wood flour/polypropylene (PP) composites and the effect of coupling agents on it, both tensile stress relaxation and compressive stress relaxation curves were determined at various wood contents (0, 20, 30, 40, 50, 60, and 70%) without a coupling agent and were also determined at 50 and 60% wood contents with different coupling agents such as maleic anhydride grafted polypropylene (MAPP) and silane. Bending modulus of rupture (MOR) and modulus of elasticity (MOE) of wood flour/PP composites at various wood contents without coupling agents and at 60% wood content with MAPP and silane as coupling agents were also tested to compare with stress relaxation results. All measurements were performed at 26 ± 1°C. Results showed that 1) the tensile stress relaxation appeared to have similar trends with compressive stress relaxation (They both declined obviously after adding coupling agents at the same wood content.); 2) wood content had a great influence on stress relaxation behavior of wood flour/PP composites (The lowest stress relaxation rates appeared at 40% wood content for both tensile and compressive stress relaxation of wood flour/PP composites without coupling agent, suggesting the best compatibility between wood and PP is at about 40% within the experimental conditions of this study.); 3) optimal loading level of a coupling agent for stress relaxation varied with type of coupling agents and wood content (Within the experimental conditions used in this study, the optimal loading level for MAPP was 2% at both wood contents, whereas for silane, it was 1.5% at 50% wood content and 2% at 60% wood content.); and 4) lower stress relaxation rates corresponded to higher bending MOR and MOE values at 60% wood content. This suggests that long-term performance of wood flour/PP composites would be consistent with bending strength at room temperature.


Bhattacharyya D, Manikath J, Jayaraman K (2006) Stress relaxation of woodfiber-thermoplastic composites. J Appl Polym Sci 102(1):401-407.nCao J, Wang Y, Xu W, Wang L (2010) Preliminary study of viscoelastic properties of MAPP-modified wood flour/polypropylene composites. For Stud China 12(2):85-89.nCao J, Xie M, Zhao G (2006) Tensile stress relaxation of copper-ethanolamine (Cu-EA) treated wood. Wood Sci Technol 40(5):417-426.nDastoorian F, Tajvidi M, Ebrahimi G (2010) Evaluation of time dependent behavior of a wood flour/high density polyethylene composite. J Reinf Plast Comp 29: 132-143.nDwianto W, Inoue M, Norimoto M (1997) Fixation of compressive deformation of wood by heat treatment. Mokuzai Gakkaishi 43(4):303-309.nDwianto W, Morooka T, Norimoto M (1998) The compressive stress relaxation of Albizia (Paraserienthes falcata Becker) wood by heat treatment. Mokuzai Gakkaishi 44 (6):403-409.nFilex J, Gatenholm P (1991) The nature of adhesion in composites of modified cellulose fibers and polypropylene. J Appl Polym Sci 42:609-620.nFu Y, Zhao G (2008) Stress relaxation of silicon dioxide-wood composite. Journal of Beijing Forestry University 30(1):119-123.nInoue M, Minato K, Norimoto M (1994) Permanent fixation of compressive deformation of wood by crosslinking. Mokuzai Gakkaishi 40(9):931-936.nKazayawoku M, Balatinecz J, Woodhams R (1997) Diffuse reflectance fourier transform infrared spectra of wood fibers treated with maleated polypropylenes. J Appl Polym Sci 66:1163-1173.nMatuana L, Balatinecz J, Park C, Sodhi RS (1999) X-ray photoelectron spectroscopy study of silane-treated newsprint-fibers. Wood Sci Technol 33:259-270.nNakano T (1996) A theoretical description of creep behavior during water desorption. Holzforschung 50(1):49-54.nOksman K (1996) Improved interaction between wood and synthetic polymers in wood/polymer composites. Wood Sci Technol 30:197-205.nOksman K, Lindberg H (1995) Interaction between wood and synthetic polymers. Holzforschung 49(3):249-254.nRaj R, Kokta B (1991) Reinforcing high density polyethylene with cellulosic fibers. I. The effect of additives on fiber dispersion and mechanical properties. Polym Eng Sci 31(18):1358-1362.nSchneider M (1994) Wood polymer composites. Wood Fiber Sci 26(1):142-151.nState Bureau of Quality and Technical Supervision (2000) Plastics—Determination of flexural properties. In Book of standards. China State Bureau of Quality and Technical Supervision, Bejing, China.nXue Z, Zhao G (2006) Strain relaxation properties of montmorilonite (MMT)-wood composite. Journal of Beijing Forestry University 28(2):115-117.n






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