Effect of surface functional modification of nano-alumina particles on thermal and mechanical properties of epoxy nanocomposites

Surface organic molecule modification of nanosized alumina particles is an effective way to improve its dispersion in polymer and to enhance the properties of polymer nanocomposites. In the present study, γ-aminopropyl triethoxysilane was used as a surface modification agent to react with the hydroxyl group on the surface of nanosized alumina. The properties of the modified alumina particles were characterized by FT-IR spectra, particle-size analyzer and transmission electron microscope (TEM). The nanocomposites of the epoxy resin filled with nano-sized alumina before and after surface modification were fabricated by physical blending. The mechanical behaviour and heat resistant properties of the composites were investigated. The results showed that the effective chemical bonds were formed between nano-alumina particles and γ-aminopropyl triethoxysilane after modification. Compared to the non-modified particles, the modified alumina nanoparticles exhibited a good dispersibility, and distributed uniformly in the epoxy matrix. The epoxy matrix filled with the modified nanoparticles showed a shorter gel time and a higher curing degree. The composites filled with modified nano-alumina revealed the optimum improvement of heat resistance. The composites with 3 wt% weight fraction modified particles had higher thermal decomposing temperature and glass transition temperature, and they were raised by 11 and 10°C relative to that of the neat resin, respectively. The modified alumina nanoparticles had better enhancement effect on epoxy matrix. The ultimate flexural strength and flexural modulus of the composites with 3 wt% modified particles increased by 55 and 77.1%, respectively; the impact strength of the composites containing 5 wt% modified particles increased by 24.7% relative to the neat resin, and the impact fracture surface presented ductile fracture features.