Studies On Silica Surface Modification And Its Influence On Structure And Properties Of Silicone Rubber

Since the advent of silicone rubber, people gradually found many unique natures that other rubber do not have, for example, high and low temperature properties, weather resistance, ozone resistance, physiological inertness, electrical insulation, etc. Thus, silicon rubber was used more and more widely in defense science and technology, health care, electronics and electrical, automotive and household goods. Silicone rubber gradually transform from special rubber to excessively large synthetic rubber. However, the low mechanical properties is the biggest obstacle to its extensive applications. In the field of silicon rubber’s reinforcement, silica is the most widely used filler, but the modification research in China is still far behind the United States, Japan and other developed countries.By this study, we discuss the modifier types, dosage, modify methods, and Sec vulcanized’s influence to the silicone rubber’s performance, and select process parameters that are more optimized to obtain silicone rubber with better mechanical properties and transparency. Study of surface modification of SiO2with Si69showed that hydrolysis time have a great impact on the degree of hydrolysis. Due to ilanol self-polymerization, with hydrolysis time increases, the degree of hydrolysis first increase then decrease. The catalytic rate is higher when using AcOH as catalyst than that of HCl. While the grafting rate is higher when we use HCl. Summarizing the data of the research, Si69is not suitable.In the second part we discussed the modification of SiO2with KH570and experimented using two methods. The results showed that compared with raw silica, the sol-gel modified silica gets better dispersion, smaller aggregates size, but lower specific surface area. The compound viscosity and mechanical properties of vulcanized rubber with sol-gel modified silica is not as good as those using mechanical blending method. But both two method cannot get good mechanical properties, indicating wet-silca in not suitable in silicone rubber reinforcement.Comparing four methods commonly used in silica modification, we found that using sol-gel method to modify fumed silica is better than mechanical blending method, dry-process and wet-process. Further experiment showed that when using Hexamethyl Disilazane (HMDS) as coupling agent for fumed silica A200, the optimum dose is6%by mass of the silica. When comparing hydrophobicity using different modification methods, we use the same amount of HMDS. The result shows that the sol-gel method modified product is not as hydrophobic as using dry method, indicating that hydrophobicity is not a determinant factor for silicon robber reinforcement. The amphiphilic architecture of HMDS allowes it to be well dispersed in silicone rubber, thus leads to better reinforcement.We also found that the amount of water used to hydrolyze HMDS greatly affects the modification of silica. With the water amount increase, the density of silica increase substantially. The dusting behavior of silica is significantly reduced, mixing process gets a lot easier, the viscosity of the compound increase at first and then decrease. With6%HMDS in mass, when the amount of water is80%in mass of HMDS, the tensile strength of the rubber filled with40phr modified silica can reach10.5MPa, while the elongation at break is456%. By increasing the filler amount to50phr, no higher mechanical properties shows. After second curing, the composite mechanical properties and transparency both declined.