When a peroxide-saturated rubber such as PE is used, the reaction mechanism is mainly to take hydrogen to form a radical, and the radical coupling to form a crosslink. When the peroxide is sulfided with PP, EPM or EPDM, there is a possibility of β-cleavage in the EPM due to the presence of a pendant methyl group in the propylene structural unit.
Therefore, a vulcanizing agent is often added to the formulation, which can shorten the vulcanization time and improve the tensile strength of the compound. Commonly used vulcanizing agents are sulfur TAIC and the like.
Peroxide-vulcanized hetero-chain rubbers such as methyl silicone rubber are similar to vulcanized polyethylene.
In addition to vulcanizing rubber, peroxide can also crosslink plastics, polyurethanes, and the like.
Peroxide vulcanization coordination points
The amount of peroxide varies with the gum grade. For the cross-linking efficiency of rubber SBR (2.5). BR (10. 5), the amount of DCP is 1.5-2.0 parts; for NR (1.0), the amount of DCP is 2-3 parts.
Acidic substances such as stearic acid and acidic fillers (such as silica, hard clay, and channel black) and substances that easily generate hydrogen ions can cause ion decomposition of peroxides and affect cross-linking, so it should be used less. Or not. Adding a small amount of alkaline substances such as triethanolamine can adjust the acidity and alkalinity and improve the crosslinking efficiency.
When peroxide is vulcanized, the role of ZnO is to improve the heat resistance of the rubber compound, rather than the activator. The role of stearic acid is to increase the solubility and dispersibility of ZnO in rubber.
The most commonly used vulcanizing agent is sulfur, about 0-3 parts, as well as TAIC, TAC, HVA-2 and the like. The amount of HVA-2 is generally from 0.5 to 0 parts.
Determination of vulcanization conditions
The peroxide vulcanization temperature of the rubber should be determined by reference to the peroxide decomposition temperature of 1 min. During the vulcanization process, the rate of decomposition of the peroxide depends on the vulcanization temperature. Generally, 6-10 times of the half-life time is passed, and the peroxide is basically consumed. Therefore, the vulcanization time is selected to set the peroxide half-life time of 6-10 times at the vulcanization temperature.