Elastic moduli and thermal conductivity of injection‐molded short‐fiber–reinforced thermoplastics

The nine independent stiffness constants of injection‐molded tensile bars of poly(phenylene sulfide) reinforced with 30 and 40% by weight of carbon or glass fibers have been measured by ultrasonic techniques. The thermal conductivities along the three principal directions of these thermoplastic composites have also been determined by the laser‐flash radiometry method. The elastic moduli (tensile and shear) and thermal conductivity increase with increasing fiber volume fraction, v_f, with the tensile modulus and thermal conductivity along the mold flow direction showing the greatest change. For a composite, containing 40 weight % of carbon fibers, the Young's modulus and thermal conductivity along this direction exceed those of the polymer matrix by a factor of 8. Using the known values of v_f and the observed aspect ratio and orientation factor of the fibers, the elastic moduli and thermal conductivity have been calculated on the basis of the laminate theory. The agreement between theoretical predictions and experimental data is better than 10% on the average.