Effects of antioxidant functionalized silica on reinforcement and anti-aging for solution-polymerized styrene butadiene rubber

Rubber materials and products are widely used in various industrial products owing to their excellent physical and chemical properties . This has attracted significant attention of many researchers who are interested in improving the functionality and service life of such products. Unfortunately, rubber materials are susceptible to aging when exposed to factors like oxygen, light, ozone among others. This is attributed to the instability of the isolated carbon double bonds and hydrogen in the molecular chains.

Among the common aging types, thermo-oxidative aging results in the premature failure of rubber products through the deterioration of their physical and chemical properties. This has further led to a waste of rubber resources which is a growing global concern. To this note, researchers have identified a reduction of the thermo-oxidative aging process as a promising solution to increase the lifespan of rubber materials.

Presently, several techniques are used to prevent this aging process. However, the addition of chemical antioxidants into the rubber matrix is preferably used. Even though the antioxidants are useful in improving the rubber thermo-oxidative stability, their migration in the matrix induced by external factors (like low pressure, high temperature) leads to a decrease in the protective effect. Therefore, chemical antioxidants developed today should take into consideration increasing the relative molecular weight, grafting on the filler surface and making the sustainable release of the antioxidants like the hollow materials.

Recent reports has shown that some antioxidant functionalized silica fillers can be used as anti-migration of antioxidant. The silica fillers can disperse homogeneously in the polymer matrix as well as improve the polymer thermo-oxidative stability. However, up to date, the effects of the reinforcement and anti-aging of the antioxidant functionalized silica for polymer have not been fully explored. Owing to the rapid development of molecular simulation technology, it has become more convenient to investigate the relationship of the properties and structures for antioxidant functionalized silica system.

Researchers at Beijing University of Chemical Technology Kaiqiang Luo, Dr. Wei Zheng, Dr. Xiuying Zhao and led by Professor Sizhu Wu in collaboration with Dr. Xiujuan Wang at Qingdao University of Science and Technology developed a new type of antioxidant functionalized silica. The antioxidant was prepared by a coupling reaction between the antioxidant coupling agent and silica. Furthermore, the effects of SiO₂-g-MC on the reinforcement and antioxidant were investigated through molecular simulation techniques as well as experimental methods. Their work is published in the research journal, Materials and Design

The authors observed that the reinforcement of SiO₂-g-MC was more effective as compared to the neat silica in SSBR matrix due to the better dispersion and the stronger interaction. In addition, SiO₂-g-MC filler could not only exhibited well vulcanization behavior, but also restrain the migration of the free MC. Consequently, SiO₂-g-MC could reduce the unnecessary negative influence of MC (or neat silica) on the cross-linking density of the composite and enhance the thermo-oxidation resistance of SSBR composite, thereby showing excellent mechanical properties in SiO₂-g-MC/SSBR composite during the thermo-oxidative aging process.

The study by Professor Sizhu Wu and her colleagues successfully developed SiO₂-g-MC that has a great potential for use as functional filler for fabrication of high-performance rubber composites. In addition, it provides an in-depth understanding of relationship between the structures and properties of the SSBR composites. Therefore, the study will advance the design of efficient antioxidants for preventing thermo-oxidative aging in rubber products thus also increasing their lifespan.