Improving thermal conductivity of polybutylene terephthalate composites with hybrid synthetic graphite and carbon fiber

Polybutylene terephthalate (PBT) is a semi-crystalline engineering thermoplastic polyester. PBT offers rapid molding cycles, high heat resistant, crystallinity, fatigue resistance, strength and rigidity, excellent electrical properties, creep resistance, reproducible mold shrinkage and chemical resistance. In this study, PBT was loaded with synthetic graphite and carbon fiber at different weight fractions (10–40 wt.%). PBT-based composites were fabricated by the melt mixing process by using a co-rotating twin screw extruder then thermal, mechanical and morphological properties of filled PBT composites was investigated. Weight fraction of carbon fiber (up to 30 wt.%) increases the tensile strength and flexural strength of PBT, but synthetic graphite loading decreases the tensile strength and flexural strength of PBT. The highest in-plane and through-plane thermal conductivity values were obtained as 9.24 for 40 wt.% synthetic graphite filled composite and 3.41 W/mK for 40 wt.% carbon fiber reinforced composite, respectively. Carbon fiber was found to be more effective in increasing the through-plane thermal conductivities than synthetic graphite.