Introduction of the Action Principle of PVC HEAT STABILIZER
The thermal degradation process of PVC is very complex, and several chemical reaction processes can be carried out at the same time: Molecular chain decomposition removing HCL, oxidative chain breaking and cross-linking, reaction of a small amount of aromatization and generation of hydrocarbon by macromolecular chain breaking The aging or carbonization of PVC caused by dehydrochlorination is the main performance of thermal degradation.
Based on the current research results, the mechanism of heat stabilizers can be classified into the following categories:
Replacing unstable allyl chloride atom or tertiary carbon chloride atom in PVC molecule to remove initiation site. For example, cadmium and zinc soaps, organotin, thiols, and antimony compounds can be easily substituted by the unstable chlorine atoms in PVC molecules.
The addition reaction with polyene structure can prevent the formation of macroconjugation and reduce coloring. If the salt or Ester of unsaturated acid contains double bond, it reacts with the conjugated double bond of PVC to destroy the conjugate structure and inhibit discoloration.
Trap free radicals and prevent oxidation and chain reaction. Such as adding human phenolic compounds, the hydrogen radical given by phenol can couple with the degraded PVC macromolecule free radical to form free radical substances which can not react with oxygen or be inert. At the same time, it can inhibit the removal of HCL and play the role of heat stabilization.
Therefore, a PVC heat stabilizer can have one or more of the above-mentioned thermal stabilization functions. The main principle is through the degradation, replacement of unstable atoms or prevent reaction to break the instability of PVC structure, so that PVC in the production process more stable.