Optimizing the injection molding process for thermally and electrically conductive, carbon fiber and carbon nanotube-reinforced poly(lactic acid) hybrid composites with enhanced mechanical properties

We produced poly(lactic acid) (PLA) matrix carbon fiber and carbon nanotube-reinforced hybrid composites with enhanced thermal conductivity (0.48-0.59 W/mK) and electrical conductivity (0.35-0.97 S/cm). The conductive fillers greatly decreased the toughness, which was compensated with oligomeric lactic acid (OLA). Since fillers and plasticizers greatly alter the flow and thermal properties of the material as well, it was necessary to optimize several parameters of the injection molding process that were predetermined based on theoretical considerations. Based on oscillatory shear rheometry, we explored the rheological behavior of the materials in a wide temperature and shear rate range for the optimum injection molding temperatures, injection volume rates. We showed that by adding 15 wt% OLA as a plasticizer to the composites, the optimal processing temperature decreased by 45-135 degrees C. This remarkable change illustrates the need for rheological studies of PLA compounds. The injection molded hybrid composites containing 5% oligomeric lactic had a tensile strength, modulus of elasticity, and work of fracture higher by 41%, 10%, and 150%, respectively, compared to samples without OLA. Optimizing the composition and the parameters of conductive hybrid composites, and the electrically conductive paths formed in them. image