Effect of hybrid nano-fillers on the mechanical, thermal and viscoelastic properties of epoxy-based polymer composites for progressive applications

Epoxy resins are widely used in aerospace, electronics and structural applications because of their excellent mechanical strength, chemical resistance and dimensional stability; however, their inherent brittleness and limited thermal resistance restrict broader multifunctional use. In this study, multifunctional epoxy nanocomposites were developed using hybrid nano-fillers consisting of silica (SiO 2 ), alumina (Al 2 O 3 ) and carbon black (CB) at a fixed total filler loading of 1 wt% with controlled hybrid ratios (1:1, 1:4 and 4:1). Surface functionalisation of the fillers using APTES, γ-methacryloxypropyltrimethoxysilane (γ-MPS) and TEPA treatments improved filler dispersion and interfacial compatibility within the epoxy matrix. Dynamic mechanical analysis revealed an increase in glass transition temperature (Tg) of up to 18 °C compared with neat epoxy, while thermogravimetric analysis showed improved thermal stability with a 22–42 °C increase in T5% degradation temperature and enhanced residual char formation. Scanning electron microscopy fracture analysis demonstrated rougher fracture morphology, reduced micro-void formation, crack-path deviation and improved filler–matrix adhesion in the hybrid systems. Fourier-transform infrared analysis further confirmed successful interfacial interactions through Si–O, carbonyl and hydroxyl-associated bonding features. Among the investigated systems, CB–Al 2 O 3 hybrids exhibited superior flexural and thermal performance, whereas CB–SiO 2 hybrids demonstrated enhanced indentation resistance and viscoelastic stability. The results indicate that surface-engineered hybrid nano-fillers provide an effective and scalable strategy for simultaneously improving the mechanical, thermal and viscoelastic behaviour of epoxy composites for lightweight structural and thermally demanding engineering applications.