| Brief introduction of stability mechanism of compound stabilizer |
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| The thermal decomposition of PVC releases HCL from the heat-sensitive part and forms double bonds in the PVC structure. Because of the high activity of propylene chloride, the reaction can proceed continuously and form conjugated double bonds, which become polyolefin structure and cause coloring of the products. When calcium zinc stabilizer is combined, first of all, zinc soap is substituted by allyl chloride, accompanied by double bond transfer. The polyene structure is destroyed and the color change is inhibited. However, zinc chloride precipitates in PVC and catalyzes HCL removal, making PVC unstable and even blackening causing bridging. Calcium soap reacts with stable chlorine atoms in PVC to regenerate zinc chloride into zinc soap by double decomposition reaction, thus activating zinc soap on the one hand, activating zinc soap on the other hand, and inhibiting the destruction of zinc chloride on the other. A large number of organic compounds can greatly improve the initial coloring of products, so they are often used in stabilizers to make up for the lack of calcium and zinc stabilizers in the early coloring. Polyols are also used in PVC calcium zinc stabilizers. Polyols inhibit degradation by chelating metal chlorides. In addition, polyols can displace propylene under the catalysis of metal salts. They also have a good effect on improving the initial coloring phase of calcium and zinc stabilizers. However, the application of polyols is seriously affected by the barotropic property, and polyols are also found in PVC products with high insulation requirements. The application of alcohol is limited. Acid absorbent can be used as an auxiliary stabilizer for PVC. It is speculated that they can degrade the reaction sites to form complexes and reduce the activity of the reaction sites, while capturing the catalytic activity of HCL can prevent the deHCL reaction from proceeding. The epoxide industry often has synergistic effects with calcium and zinc stabilizers. In short, the composite heat stabilizer is beneficial to large-scale production, and provides a new direction for the development of lead salt heat stabilizer. The content of lead is an important index of compound lead salt stabilizer. At present, the content of lead in compound lead salt stabilizer is generally 20% - 60%; the amount of lead used in PVC plastic door and window profiles is 3.5 - 6 phr. Key words: stabilizer, methyl tin stabilizer, internal and external sliding agent PVC |
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