Stabilization mechanism of PVC calcium-zinc stabilizers

Various causes of PVC degradation
1) Thermo-oxidative decomposition
2) Cross-linking of large radicals in the absence of oxygen; and
3) The effect of stereoconformity on degradation; and
4) Photodegradation
5)oxidative dehydrogenation of HCl; and
6)radiation degradation; and
7)molecular chain breakage due to critical stresses introduced by processing; and
8) the effect of branching point on degradation in PVC molecule, etc.
Dehydrogenation of PVC
1)The presence of activated groups on the PVC chain, usually above 100 ℃ will easily occur in the degradation reaction of de-HCl; 2)The process of de-HCl degradation of PVC is very easy.
2)De-HCl process is an autocatalytic process, which will trigger the chain decomposition of macromolecular chain to de-HCl.
3) When there are 6 or 7 polyene structures in a conjugated system, the PVC molecule absorbs ultraviolet light, thus showing a yellow color.
4) As the de-HCl process continues, the double bond increases, PVC color continues to darken and even coking, cross-linking, Z after the chain break.
PVC stabilizer should have the function
1)It can replace the active and unstable chlorine atoms in the molecule and inhibit the dehydrogen chloride reaction.
2) It can absorb or neutralize the HCl removed during processing and use, and terminate its autocatalytic effect.
3)It can carry out double bond addition reaction with polyene structure to eliminate or slow down the discoloration of products; and
4)Capture free radicals and adsorb ionic impurities to improve the activation energy of PVC to remove HCl.