Thermo-mechanical performance of multi-walled carbon nanotube-modified epoxy in filament-wound CFRP tubes under elevated temperature

This study examines the thermomechanical performance of filament-wound carbon fiber-reinforced polymer (CFRP) tubes fabricated with multi-walled carbon nanotube (MWCNT)-modified epoxy matrices at concentrations of 0, 0.25, 0.5, 0.75, and 1.0 wt%. Hoop tensile testing was conducted in accordance with ASTM D2290 at temperatures from ambient (22.5 °C) to 200 °C, complemented by differential scanning calorimetry (DSC) and multi-scale fractographic analysis. At room temperature, MWCNT addition progressively enhanced hoop strength to a peak of 343.08 ± 54.98 MPa at 0.75 wt% — a 37.5% improvement over the unmodified (MWCNT-free) CFRP tube — before declining at 1.0 wt% due to nanotube agglomeration. DSC revealed a corresponding thermal peak elevation to 170.75 °C at the same loading, while the glass transition temperature remained near 60 °C across all formulations, confirming that MWCNTs modify interphase relaxation behaviour without restructuring the bulk crosslink network. Two-way ANOVA identified test temperature as the dominant factor governing all mechanical responses, with the temperature–MWCNT interaction significant for both strength and modulus, demonstrating concentration-dependent reinforcement efficiency. SEM fractography established three temperature-dependent damage regimes: cohesive matrix fracture with active MWCNT toughening (ambient–50 °C), mixed-mode interfacial debonding (100–150 °C), and adhesive fiber–matrix separation (200 °C). These results identify 0.5–0.75 wt% as the optimal MWCNT modification window for filament-wound CFRP tubes in elevated-temperature service.