Antioxidants

tech.topic

Equistar Technical Tip

Additives: Antioxidants

Equistar Technical Tip

Additives: Antioxidants (Continued)

Thioesters perform a role similar to that of secondary A/Os in that they decompose the hydroperoxides [ROOH] into alcohols and other non-reactive species. But they also have a synergistic effect with primary A/Os, especially with the high molecular weight, hindered phenol type of primary A/O. The particular method by which the thioesters

decompose hydroperoxide radicals is not well known but is theorized to be similar to that of the secondary A/Os.Thioesters are usually used in end products with requirements that include long-term exposure to high temperatures, such as under-the-hood automotive

applications and home appliances. Thioesters have been shown to be quite effective at temperatures greater than 122°F (50°C). Even at these high temperatures, these A/Os can deactivate up to 55 molecules of hydroperoxide for every molecule of thioester.

A certain minimum amount of antioxidant is necessary to stabilize and protect polyoleins from autoxidative degradation. Primary antioxidants and thioesters are added to the polymer to provide end use product stability while secondary antioxidants are added to provide color and processing stability during pelletization and

extrusion/molding. As the temperatures of the finished part must withstand rise, so must the level of antioxidants in the polymers to prevent long-term degradation.