Effect of Nano Cerium Oxide on Heat Resistance of Silicone Rubber

As an effective heat-resistant silicone rubber additive, nanometer cerium oxide plays an important role in silicone rubber products. The main chain of the silicone rubber molecule is alternately composed of silicon atoms and oxygen atoms. The bond energy of the silicon-oxygen bond is 370kJ·mol - 1, which is much larger than the carbon-carbon bond energy of general rubber of 240kJ·mol - 1. Therefore, its thermal Good stability. With the development of high and new technologies, people have put forward higher requirements for the heat resistance of silicone rubber. Adding cerium oxide with particles as small as a certain level as a heat-resistant additive to silicone rubber can prevent oxidative cross-linking of silicone rubber side chains and improve the thermal oxidation stability of the side groups.

It can be seen from the table that after hot air aging at 250 ℃ and 3 parts, the heat resistance of MVQ vulcanized rubber is significantly improved, the Shore A hardness increases by 8 degrees, and the tensile elongation decreases by 51%; as the amount of nano-cerium oxide further increases, the heat resistance of MVQ vulcanized rubber increases. The improvement levels off. Under normal circumstances, the appropriate amount is selected in the test to have the best heat resistance and the least impact on the overall performance of the vulcanized rubber. Therefore, the dosage of nano-cerium oxide is selected to be 2 parts.

Silicone rubber mainly undergoes thermal rearrangement and degradation of the main chain in a high-temperature, airtight, oxygen-free state, that is, a depolymerization reaction occurs, making the product soft (or softened), resulting in the loss of mechanical strength and use value. Under high-temperature aerobic environmental conditions, oxidation of polymer side groups mainly occurs, forming alkyl radicals. The coupling reaction of free radicals leads to an increase in the cross-link density of the seal, causing the product to gradually harden and even crack (called hardening). Adding cerium oxide to silicone rubber can prevent oxidative cross-linking of polysiloxane side chains and cyclization degradation of the main chain. It can prevent the free radical reaction caused by oxidation in silicone rubber within a certain temperature range, and can be regenerated under the action of O2 in the air; by absorbing certain trace amounts of acid or alkaline substances in silicone rubber that can catalyze the degradation reaction, thereby thermally stabilizing silicone rubber. At the same time, the special electronic structure of cerium oxide (the f electron layer is not filled) makes it easy to form complexes. The formed complexes inhibit the swelling of the rubber in the solvent by preventing the chain segment movement of the rubber molecules, thereby improving the rubber's strength. Oil resistance.