Cryogenic-treated surface-modified hybrid nanofillers for enhanced mechanical performance and thermal stability of epoxy nanocomposites

Conventional single nanofillers enhance the properties of epoxy composites. However, improving mechanical strength, thermal stability, and interfacial performance. It remains challenging because each reinforcement provides only limited toughening mechanisms. In this study, a hybrid reinforcement strategy combining graphene oxide (GO), aluminum oxide (Al₂O₃), and ceramic particles (CP) was used as a filler through cryogenic pretreatment to composite fabrication. Instead of cryogenic treatment of the cured composite. The fillers were cooled to −196 °C at a controlled rate of 3 °C min⁻¹ , maintained for 30 min, and subsequently warmed to room temperature before incorporation into the epoxy matrix. A compression moulding machine was used to fabricate the eight composite plates, including neat epoxy, single-filler, and hybrid-filler systems. The structural evolution, chemical interactions, thermal stability, and mechanical performance were investigated using a field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), indentation testing, and flexural testing. XRD confirmed the existence of graphitic and ceramic phases. The balanced GO–CP hybrid exhibited an enlarged interlayer spacing of 5.52 Å, indicating improved filler dispersion after cryogenic pretreatment. FTIR revealed enhanced hydrogen-bonding interactions and filler–matrix compatibility without altering the cured epoxy network. TGA showed an improvement in thermal stability, with delayed degradation and the highest residual char yield observed. The indentation hardness increased from 22.8 ± 0.7 HV for neat epoxy to 44.5 ± 1.2 HV, with an improvement. Whereas the flexural strength increased from 86.8 ± 2.3 MPa to 156.8 ± 3.6 MPa, by a 69.5% increase in flexural modulus. FESEM observations further confirmesd that the hybrid reinforcement improved homogeneous filler dispersion, crack deflection, crack bridging, and particle pinning in the matrix. The results demonstrate that cryogenic pretreatment combined with balanced hybridization of graphene oxide and ceramic particles provides a simple and effective approach. It enhanced the structural integrity, thermal resistance, and mechanical performance of epoxy composites.