Effect And Mechanism Of Iron Oxide Modified Carbon Nanotubes On Thermal Oxidative Stability Of Silicone Rubber

Silicone rubber (SR) as one of the most important synthetic rubbers is known toexhibit excellent thermal oxidative stability over conventional carbon backbonerubbers With the rapid development of science and technology, a demand for thermalresistant silicone rubber, has increased greatly. A lot of researches focus on theimprovement of thermal stability of silicone rubber. There are many methods forimproving the thermal oxidative stability of silicone rubber. Adding thermal resistantadditives into silicone rubber matrix is the most common one.In our previous research, we had found the presence of carbon nanotubes (CNTs)affected the crystalline form of attaching iron (III) oxide, which was changed from αto γ. When iron oxide modified CNTs (γ Fe2O3CNTs) were added into SR matrix,they could remarkably improve the mechanical properties of SR based composite afterthermal oxidative aging; at the same addition amount, their effect was superior toCNTs, γ Fe2O3, or a mixture of both. This phenomenon may be attributed to thesynergistic effect of γ Fe2O3and CNTs.To investigate the effects of iron oxide attached on CNTs surface on the thermaloxidative stability of silicone rubber deeply, a series of γ Fe2O3CNTs with differentsizes or loadings of γ Fe2O3were prepared. Transmission electron microscopy (TEM)and X ray diffraction (XRD) were performed to characterize the additives; bycomparing the mechanical properties of SR composites after aging, the optimalexperimental group S9was obtained, in which, all the iron oxides existing in acrystalline form of γ Fe2O3were attached on CNTs surface uniformly with a size ofabout5~10nm. The corresponding composite S9/SR had the maximum retention ratesof tensile strength and elongation at break, about91.4%and96.9%, respectively.What’s more, the action mechanism of γ Fe2O3CNTs on the thermal oxidativedegradation of SR composite was studied by measuring the average molecular weightbetween crosslinking points (Mc) of SR before and after aging, as well as by detectingthe degradation products of SR by thermogravimetric analysis/infrared spectrometry(TG IR). The results indicated that γ Fe2O3CNTs could not only increase the initialformation temperatures of degradation products, but also decrease the concentrationsof products from the oxidation and fracture of side chains of SR. All the aboveinfluences contributed to the improvement of the thermal oxidative stability of SR.