Synthesis and mechanical properties of the epoxy resin composites filled with sol−gel derived ZrO₂ nanoparticles

Highly dispersive ultrafine zirconia nanoparticles were prepared by a modified sol-gel process and used as fillers added into epoxy resins. Meanwhile, surface modification and ultrasonic mixing process was utilized to achieve homogenous dispersion of the nanoparticles in epoxy resin. The obtained zirconia nanoparticles showed a mainly tetragonal crystalline structure with an average particle size of 11 nm and a specific surface of 53.68 m² g⁻¹ as detected by XRD analysis, SEM measurements, laser diffraction particle size analyzer, and physisorption apparatus. TEM observations indicated that the nanoparticles modified by KH-550 had better dispersion in the epoxy matrix. FTIR verified that KH-550 successfully grafted onto the surface of zirconia nanoparticles. Several mechanical tests demonstrated the increased mechanical properties for the composites with lower nanoparticle content, which was ascribed to the good dispersion of zirconia nanoparticles in the epoxy resin and improved particle/matrix interface adhesion. The optimal mechanical properties were found when zirconia nanoparticle content is around 3 wt%. Moreover, the maximum tensile strength, tensile modulus, fracture toughness, critical strain energy release rate, and hardness increased by 44%, 29%, 63%, 122 and 17 % compared with the neat epoxy resin, respectively. Results of thermal analysis revealed that the char yield of the composites were significantly improved due to the incorporation of nanoparticles and additional crosslinkage between nanoparticles and matrix.