Hybrid Carbon-Reinforced PBT Nanocomposites: Toward Energy-Efficient and Conductive Polymer Systems

This study develops polybutylene terephthalate (PBT)-based nanocomposites reinforced with milled micrometer carbon fiber (MCF), chopped micrometer carbon fiber (CF), and carbon nanotube (CNT) masterbatch using a multiscale hybrid reinforcement strategy. Comprehensive characterization, including field emission scanning electron microscopy (FESEM), confirmed the morphology of the fiber matrix, and the maximum value obtained of melt flow index (MFI) was 83 g/10min. Rheological percolation occurred at 1–5 wt.% CNT, but higher CNT content impaired processability due to excessive viscosity. DSC revealed increased glass transition (Tg) and crystallization temperatures (Tc), indicating enhanced thermal stability. Mechanical tests showed improved elastic modulus (E) in (MCF: 3.92 GPa; CF: 5.37 GPa) but reduced flexural strength (σf) and strain (ɛf). Electrical percolation occurred at higher filler levels, resulting in voltage-independent resistivity. Furthermore, Joule heating tests showed significant temperature increases (10–20 wt.% CNT), while CF and MCF showed minimal thermal response. These results highlight the interplay between filler content, percolation, and multifunctional performance, offering insights into designing advanced conductive polymer composites for applications in filters, pumps, electrostatic discharge protection, fuel sensing, and energy-efficient systems.