EFFICIENCY OF REINFORCING MATERIALS IN FILLED POLYMER COMPOSITES

The rule of mixtures was used as the basis for the development of a si mple mathematical model that allows comparison of the efficiency of st iffness reinforcement by fillers in a filled plastic composite. Based on an estimate for the stiffness of the wood fiber, a reinforcement ef ficiency factor is deduced from experimental data on filled polymer co mposites through the use of a curve-fitting algorithm. Polyethylene, p olypropylene, polystyrene, and styrene-maleic anhydride copolymer syst ems were used as the matrix phases. Fillers studied were glass fiber, straw flour, thermomechanical pulp, and wood flour. Theory suggests th at an improvement in stiffness of a factor of approximately two to fou r may be possible, depending upon the system. The simple theory consid ered here is not helpful in comparing ultimate stress (or strength) va lues among different filled polymer systems. Wood-reinforced styrene-m aleic anhydride copolymers were stronger than wood-filled polystyrene systems.