Heat stabilizers.

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