those who can improve the thermal stability of the polymer additives are known as heat stabilizers

Broadly speaking , those who can improve the thermal stability of the polymer additives are known as heat stabilizers. Because of the poor thermal stability of PVC , so most of the world are used for PVC stabilizer PVC . Therefore , the commonly used stabilizers for PVC means polyvinyl chloride and copolymers of heat stabilizers.
Generally in accordance  low molecular polyethylene with the chemical composition of a heat stabilizer to the classification can be as basic lead salt , a metal soap, organic tin , epoxy compounds, phosphorous esters, polyhydric alcohol. In terms of the role of size can be divided into the main stabilizers for PVC stabilizers and auxiliary stabilizers. Auxiliary stabilizing agent itself or only a small stabilizing effect without thermal stability , but it and the primary stabilizing agent and having a synergistic effect ; primary stabilizer is generally a metal-containing heat stabilizer. And epoxy compounds, phosphites , polyols and other pure compounds are generally used as an auxiliary stabilizer .
As to achieve good stability of PVC often need to use a variety of pvc heat stabilizer , so that some products is a combination of stabilizers for PVC component complex , a composite stabilizer , such as barium cadmium stabilizer, barium zinc stabilizer etc. , these composite stabilizer usually has joined the PVC processing lubricants and other additives needed to facilitate the users. Many varieties of composite stabilizer organic pigments  with powder, paste , liquid, three forms [ 1 ]
( 1 ) absorption of hydrogen chloride
Me (OOCR) 2 + 2HCl === MeCl2 + 2HOOCR
Wherein Me is : Pb, Ba, Cd, Ca, Zn, Sn, Sb, Mg, Sr , etc.
( 2 ) eliminate the instability of the chlorine atoms substituted or eliminate unstable chlorine atom.
( 3 ) to prevent the auto-oxidation of PVC in the  magnesium hydroxide flame retardant hot oxygen and shear stress , easily oxidized by O2 degradation .
( 4 ) metal salts of maleic acid, or to inhibit or eliminate the double bond becomes shorter and less .