The effect of recycling on the time-dependent behavior of polycarbonate reinforced with short glass fibers

Observations are reported on virgin, recycled and a mixture of virgin and recycled polycarbonates reinforced with various amounts of short glass fibers (1) in tensile tests with a constant strain rate and (2) in oscillatory torsion tests at room temperature. A constitutive model is developed for the viscoelastic and viscoplastic behavior of a polymer composite with a glassy matrix. The composite is treated as an equivalent ensemble of meso-regions linked with each other. With reference to the theory of cooperative relaxation, the viscoelastic response is attributed to rearrangement of meso-domains. The viscoplastic behavior reflects sliding of meso-regions with respect to each other. The rate of sliding is proportional to the rate of macro-deformation. Constitutive equations for isothermal three-dimensional deformation with small strains are derived by using the laws of thermodynamics. The stress–strain relations are determined by five adjustable parameters that are found by fitting the experimental data. The study concentrates on the effects of filler content and recycling of the host matrix on the mechanical properties of composites.