Heat stabilizers.

Heat stabilizers are added to polymers to prevent their degradation due to heating.
These substances are added into a material to protect them when subjected to intense thermal process.
In case of chlorine containing polymers such as PVC on heating loses HCl i.e dehydrohalogenation and forms chromophoric conjugated polyenes structure as shown in figure below.

Degradation of PVC on heating.
These allylic chlorides are unstable and degradation continuous as an unzipping type of chain reaction.
This degradation is accelerated by the presence of iron salts, oxygen and hydrogen chloride.
The addition of organic phosphites such as mixed alkyl and aryl phosphites or triphenyl phosphites, form complexes and prevent the formation of insoluble chlorides.
Toxic heat stabilizers such as Lead, Cadmium and Barium salts act as HCl scavengers.

Epoxy group act as HCl scavenger.

Less toxic epoxidised, unsaturated oils such as soybean oil act as HCl scavenger.Additives

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Polymers

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