Heat stabilizer action:
(1) Eliminate the initiator of PVC pyrolysis, such as allyl chloride and unsaturated bond in PVC;
(2) Eliminate all the catalytic substances for thermal degradation, such as hydrogen chloride liberated from PVC.
Therefore, the heat stabilizer selected and used should have the following functions:
① It can replace the active atoms (e.g., allyl chlorine atoms) in the chain to form a more stable chemical bond to reduce the possibility of deHCl;
② It can absorb HCl quickly and inhibit its autocatalysis;
③ can be added with the double bond in PVC to form saturated polymer chain;
④ It can inhibit the oxidation and cross-linking of polyene structure;
⑤ affinity for PVC, and is non-toxic or low toxic;
⑥ Not with PVC additives, such as plasticizer, filler and so on.
The current use of heat stabilizer can not fully meet the above requirements, so in the process of use must be combined to make the stability requirements of the selection of different properties of heat stabilizer. Sometimes it must be used in conjunction with antioxidants, light stabilizers and other additives to reduce the possibility of oxidative aging.