The role of stearic acid and zinc oxide in rubber formulations

To a certain extent, zinc stearate can partially replace stearic acid and zinc oxide, but stearic acid and zinc oxide in rubber cannot completely react and have their own effects.

Zinc oxide and stearic acid form an activation system in the sulfur vulcanization system, and its main functions are as follows:

1. Activation vulcanization system:

ZnO reacts with SA to generate zinc soap, which improves the solubility of ZnO in rubber, and interacts with accelerators to form a complex with good solubility in rubber, activates accelerators and sulfur, and improves vulcanization efficiency.

2. Increase the cross-linking density of vulcanizates:

ZnO and SA form a soluble zinc salt. The zinc salt is chelated with the cross-linked bond, which protects the weak bond, causes the vulcanization to form a short cross-linked bond, adds new cross-linked bonds, and increases the cross-linking density.

3. Improve the aging resistance of vulcanized rubber:

During the use of vulcanized rubber, the polysulfide bond breaks and the generated hydrogen sulfide will accelerate the aging of the rubber, but ZnO reacts with hydrogen sulfide to generate zinc sulfide, which consumes hydrogen sulfide and reduces the catalytic decomposition of hydrogen sulfide on the cross-linked network; in addition, ZnO can sew broken sulfur bonds and stabilize cross-linked bonds.

4. Different reflection mechanisms:

In different vulcanization coordination systems, the mechanism of action of different vulcanization accelerators is very different. The effect of ZnO and SA reaction to form a zinc stearate intermediate is also different from that of using zinc stearate alone.