Causes of PVC degradation

1) Thermal oxidation decomposition;

2) Increase the cross-linking of large free radicals in the absence of oxygen;

3) The influence of stereoregularity on degradation;

4) Light degradation;

5) Oxidative removal of HCl;

6) Radiation degradation;

7) Molecular chain scission caused by critical stress introduced during processing;

8) The influence of branch points in PVC molecules on degradation, etc.

De-HCl degradation of PVC

1) There are activated groups on the PVC chain, and the degradation reaction of HCl removal usually occurs above 100°C;

2) The HCl removal process is an autocatalytic process, which will cause the chain decomposition of macromolecular chains to remove HCl;

3) When there are 6 or 7 polyene structures in a conjugated system, the PVC molecule absorbs ultraviolet light, thus showing yellow;

4) As the process of removing HCl continues, the double bond increases, and the color of PVC continues to darken, even coking, crosslinking, and finally chain scission.

Functions of PVC stabilizers

1) It can replace the active and unstable chlorine atoms in the molecule and inhibit the dehydrochlorination reaction;

2) It can absorb or neutralize the HCl released during processing and use, and terminate its autocatalysis;

3) It can carry out double bond addition reaction with polyolefin structure to eliminate or slow down the discoloration of products;

4) Capturing free radicals and adsorbing ionic impurities to improve the activation energy of PVC removal of HCl.