Meaning
Secondary antioxidants protect polymers from thermal-oxidative degradation by decomposing hydroperoxides into non-radical species during melt processing. Using organophosphites in resin formulations ensures that the polymer chains do not undergo scission or crosslinking when exposed to high heat and shear. These additives are consumed during processing to protect the virgin polymer.
They are essential for maintaining the melt flow index of the resin.
Melt Stabilization
During melt processing, high temperatures and shear forces trigger polymer oxidation. When organophosphites are present, they react with hydroperoxides to form stable phosphates.
Colour Prevention
Oxidation reactions can produce chromophores that cause the polymer to turn yellow or brown during processing. The addition of organophosphites helps prevent this discoloration by interrupting the chemical pathways that lead to these color-generating compounds. This protection is necessary for maintaining the high aesthetic standards of clear packaging and consumer electronics housings.
It allows moulders to use higher levels of regrind without sacrificing the optical clarity of the finished parts.
Hydrolytic Stability
The chemistry of secondary antioxidants makes them sensitive to moisture during storage and handling. Many organophosphites can undergo hydrolysis when exposed to humid conditions, which reduces their effectiveness and produces acidic byproducts. Compounders must select phosphites with high hydrolytic resistance to prevent this degradation.
Protecting the additive from moisture before compounding ensures that it can perform its role during melt processing. This selection is crucial for resins that are stored for long periods in humid environments.
