Polyvinyl chloride (PVC) is the most produced plastic polymer after polyethylene and polypropylene. Eugene Bowman discovered the polymer in 1872, when he observed that some of the vinyl chloride in the flask began to polymerize in a white solid under sunlight. However, only after B.F. Goodrich developed a method to plasticize rigid, brittle polymers by mixing PVC with several additives, PVC has become more widely used in commercial products.
Polyvinyl chloride is a relatively low cost polymer material with good chemical and biological properties and good processing properties. However, unmodified polymers must always be associated with additives such as heat stabilizers and UV stabilizers, flame retardants, smoke suppressants, plasticizers, processing aids, impact modifiers, thermal modifiers, pigments and The filler) is mixed and converted to a compound. The choice of additives depends on the desired function, depending on the application.
When exposed to heat (> 100o C), HCl is eliminated from the polymer backbone. This HCl triggers a further autocatalytic degradation process, causing rapid discoloration and embrittlement of the PVC. Heat stabilizers can greatly increase the heat stability by various mechanisms.In PVC formulations, phosphite antioxidants act as chelating agents, and complex metal chlorides can enhance PVC products, coloring, heat resistance and weatherability, and maintain transparency. It also works with epoxy organotin compounds and exhibits synergistic effects. It can reduce the amount of primary stabilizer, especially the amount of expensive organotin stabilizer.
Phosphite antioxidants can be used in a variety of composite stabilizers, particularly in clear PVC products, typically in amounts ranging from 10% to 30%.
Phosphite and phosphonite esters are used on a large scale for the stabilisation of polymers against degradation during processing and long-term applications. They function as antioxidants by various mechanisms depending on their structure, the nature of the substrate to be stabilised and the reaction conditions.
All phosphites and phosphonites are hydroperoxide-decomposing secondary antioxidants. Their reactivity in hydroperoxide reduction decreases with increasing electron-acceptor ability and bulk of the groups bound to phosphorus in the order phosphonites > alkyl phosphites > aryl phosphites > hindered aryl phosphites.
Five-membered cyclic phosphites are capable of decomposing hydro-peroxides catalytically due to the formation of acidic hydrogen phosphates by hydrolysis and peroxidolysis in the course of reaction. The o-hydroxyphenyl phosphates formed in this way from o-phenylene phosphites are excellent chain breaking antioxidants.
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