The effects of wood flour content and coupling agent on the dynamic mechanical and relaxation properties of wood-plastic composites

This research studied the influence of formulations of wood-plastic composites on dynamic mechanical properties—storage modulus (E′), loss modulus (E′′) and mechanical loss factor (tan δ)—according to dynamic mechanical analysis spectra. The specimens were made with wood flour, high-density polyethylene (HDPE) and maleic anhydride polypropylene as a coupling agent. Generally, the presence of fillers and a coupling agent in polymer affect the relaxation processes and produce a more complex morphology, thereby influencing the mechanical and viscoelastic properties of the composites. In this work, the addition of a higher content of wood flour resulted in higher values of E′, indicating a better stiffness, but tan δ decreased. The bonding agent significantly improved E′, which can be attributed to an enhanced interface between the wood and the HDPE. Coupled products had better E′ retention at elevated temperatures than uncoupled samples. The addition of wood flour and a coupling agent increased the value of E′, but did not significantly change the range of relaxation transition.