Meaning
A type of secondary antioxidant provides processing stability to polymers by decomposing hydroperoxides into stable alcohols. The secondary phosphite works alongside primary antioxidants to protect the resin during the high heat of extrusion and injection moulding. This additive is necessary for preventing the loss of molecular weight and the color changes that occur during manufacturing.
Hydrolytic Stability
Resistance to moisture is a major factor in the performance of these chemicals. A secondary phosphite must be able to withstand storage in humid conditions without breaking down into acidic byproducts. High quality grades are designed to be hydrolytically stable, which prevents them from causing black specks or plate-out on the mould surface.
Processing Protection
Rapid reaction with hydroperoxides prevents the initiation of the auto oxidation cycle. Because the secondary phosphite is so effective at high temperatures, it is used to protect the polymer during multiple heat cycles, such as when regrind is added back into the process. This protection ensures that the melt flow index of the material remains stable from the beginning of the run to the end.
Synergistic Effect
Pairing this additive with a hindered phenol creates a stabilization system that is more effective than each chemical acting alone. The secondary phosphite takes care of the melt processing phase, while the primary antioxidant provides long term protection during the life of the part. This dual approach is used in almost all polyolefin resins to ensure they meet the demanding requirements of modern industrial and consumer applications.
The chemical interaction between these two stabilizers allows the polymer to maintain its mechanical properties even after being subjected to the extreme shear and heat of a modern high speed production environment.
