Carbonaceous filler and fiber hybridization for enhanced mechanical, thermal, and electrical properties of polymer composites: a review

Abstract
This review critically examines the impact of carbonaceous nanofillers and fiber hybridization on the mechanical, thermal, and electrical characteristics of polymer composites. Advanced nanofillers such as graphene, carbon nanotubes, and carbon black are assessed for their potential to improve strength, conductivity, and thermal stability. Micro and macro-scale fibers (including carbon, glass, Kevlar, and natural fibers) are examined in hybrid configurations with thermoplastic and thermoset polymer matrices. Literature published between 2000 and 2025 was identified through a structured literature search of Scopus, Web of Science, and Google Scholar and synthesized to elucidate comparative performance trends. The review highlights dispersion strategies, interfacial engineering, and surface modification techniques that influence filler-matrix and fiber-matrix interactions, particularly emphasizing synergistic reinforcement mechanisms such as multi-scale interactions via crack-bridging by fibers and crack-deflection by nanofillers, along with the essential function of the interphase region in effective load transfer. Comparative analyses across reported studies demonstrate substantial improvements in tensile strength, flexural modulus, and thermal and electrical conductivity, often exceeding predictions based on the rule of mixtures. However, challenges remain in controlling nanofiller dispersion, maintaining strong interfacial compatibility, achieving effective hybridization, balancing multifunctional properties without performance trade-offs, ensuring scalable processing, and improving recyclability. The review integrates mechanistic insights and design methods to enlighten the development of high-performance, multifunctional polymer composites for aerospace, automotive, electronics, and construction applications.