Meaning
A secondary antioxidant reacts with unstable oxygen compounds to prevent the chain scission of polymer molecules. The hydroperoxide decomposer converts these reactive species into stable, non-radical alcohols before they can split and trigger further degradation. Most phosphites and thioesters function in this role, providing a necessary layer of protection during the melt stage.
Melt Protection
Processing at high temperatures generates hydroperoxides that are extremely sensitive to further heat. A hydroperoxide decomposer acts quickly during extrusion to neutralize these chemicals, which prevents the polymer from thinning or crosslinking. This protection is what allows resins to be reprocessed as regrind without a total loss of mechanical properties.
Additive Interaction
Performance of the primary antioxidant is preserved when the secondary stabilizer is present. Without a hydroperoxide decomposer, the primary antioxidant would be consumed much faster as it tries to handle the flood of radicals. Using both types of chemicals together ensures that the polymer is protected both during the manufacturing process and throughout its outdoor life.
Chemical Selection
Different molecules are chosen based on the temperature of the melt and the final application of the part. Some hydroperoxide decomposers are better suited for long term underground use, while others are optimized for the extreme heat of a thin wall injection moulding machine. Selecting the right chemical ensures that the resin remains stable under the specific stresses it will face.
The ability of the additive to remain active at high temperatures determines the maximum number of heat cycles the polymer can endure before its molecular weight drops below a usable level.
