Zinc Oxide as Rubber Vulcanizing Activator

- May 10, 2018 -

As a rubber vulcanization activator, zinc oxide has been widely used due to its full function. So far, zinc oxide is still the best activator of natural rubber sulfur sulfur. Zinc oxide, stearic acid, sulfur, and accelerators together form a vulcanization system. Zinc oxide and stearic acid form zinc stearate that accelerates sulfur vulcanization with accelerators. If sulfur is used alone, vulcanization can take a long time.

However, in the production, processing, and recycling of rubber products, the release of zinc can adversely affect the environment and human health, especially aquatic organisms. The new trend in rubber industry production is to reduce the zinc content in the products and look for possible alternatives. Instead of zinc oxide, metal oxides or metal complexes were used in the study. Zinc oxide reduction studies were carried out in compound formulations. Rheological behavior and physical properties of vulcanizates were reviewed. Magnesium oxide or magnesium stearate was used as a Activators in natural rubber formulations are feasible.

Formulations and compounds:

1, pure rubber formula

A typical formulation of sulfur vulcanizate in natural rubber contains 5 parts of zinc oxide. Five zinc oxide pure gel formulations were used as reference formulations in the study. First of all, the effectiveness of the metal oxide, magnesia, as the activator of the neat rubber formulation was examined. The zinc oxide was not added to the formula, but magnesium oxide was added, and its amount varied from 1 part to 5 parts. Magnesium stearate was tested in the same manner to determine the appropriate amount.

In order to reduce the content of zinc oxide in the formulation of natural rubber compounds, it is necessary to consider the reduction of zinc oxide in combination with the use of magnesium oxide, and use 5 parts of zinc oxide as the blank reference formulation. That is, zinc oxide is reduced to 3 parts, 2 parts and 1 part, while the amount of magnesium oxide is changed from 1 part to 5 parts.

2, carbon black filling compound

In the carbon black filled formulation, the amount of zinc oxide was reduced to 2 parts using 50 parts of N110 carbon black. Magnesium stearate and magnesium oxide vary from 1 part to 2 parts. The compound was mixed on a 12" x 6" two-roll mill and the temperature was maintained at 70C. The batch mixing time was 10 minutes.

3, test methods

The Mooney viscosity of the rubber and Mooney scorch were measured using a single-speed Mooney viscometer. The Monashon rheometer was used to determine vulcanization characteristics such as cure time (t90), scorch time (ts2), minimum torque (Ml) and maximum torque (Mh). The physical test uses a 160°C cure test piece.