Properties of Transfer-Molded Wood-Fiber/Polystyrene Composites

Bei-Hong Liang, Laurence Mott, Stephen M. Shaler, Gerard T. Caneba


Transfer-molded composites combining polystyrene, wood particles, and three bi-functional coupling agents were prepared and evaluated for physical and mechanical properties. Pure 685D polystyrene (PS) (75-100% by weight) was combined with 100-mesh (0.15-mm sieve opening) particles prepared from thermomechanically pulped quaking aspen (Populus tremuloides) (0-25% by weight). Three coupling agents, polystyrene/poly(methacrylic) (both low and high molecular weight) and polystyrene/poly(vinyl acetate) developed at Michigan Technological University, were added in an effort to promote compatibility between the hygroscopic wood fiber and the non-polar hydrophobic polystyrene. Mechanical tensile testing was used to assess the respective composite's tensile elastic modulus and tensile strength. A polystyrene/poly(methacrylic) acid (PS-PMAA) coupling agent was found to be the most effective with regard to enhanced tensile elastic modulus at higher fiber-loading levels (enhancement levels of 11.3-23.8% over pure PS). A fiber/PS composite using low molecular weight PMAA (PS-PMAAL) as a coupling agent demonstrated the best tensile strength retention characteristics at higher fiber-loading levels. Initial results show high variability in material properties over the range of fiber-loading levels, and between coupling agent type. It is clear, however, that certain coupling agents do have a positive effect on composite properties.


Composite;coupling agent;mechanical properties;polystyrene;tensile strength;transfer molding;wood fiber

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