- Nov 10, 2018 -
What are PVC stabilizers?
1) Salt-based thermal stabilizers: Salt-based stabilizers refer to lead salts of inorganic and organic acids combined with "salt-based". These stabilizers have excellent heat resistance, weatherability and electrical insulation, low cost, poor transparency, and certain toxicity. Their dosage is generally 0.5%~5.0%.
2) Fatty acid heat stabilizers: These heat stabilizers refer to compounds composed of fatty acid radicals and metal ions, also known as metal soap heat stabilizers, whose properties are related to the types of acid radicals and metal ions, and the general dosage is 0.1%~3.0%.
3) Organotin thermal stabilizers: These thermal stabilizers can form ligands with unstable chlorine atoms in polyvinyl chloride molecule, and replace carboxylic ester groups of organotin with unstable chlorine atoms in the ligands. This kind of heat stabilizer is characterized by high stability, good transparency, excellent heat resistance, and the disadvantage is its high price.
4) Compound heat stabilizers: These heat stabilizers are liquid or solid complexes based on salts or metal soaps and organotin-based complexes, in which metal salts include calcium-magnesium-zinc, barium-calcium-zinc, barium-zinc and barium-cadmium, and commonly used organic acids such as organic fatty acids, naphthenic acid, oleic acid and benzoic acid. Salicylic acid and so on.
5) Organic compound heat stabilizers: Apart from a few main stabilizers (mainly nitrogen-containing organic compounds) which can be used alone, these heat stabilizers also include polyols and phosphite with high boiling point. Phosphite is often used with metal stabilizers to improve the weatherability, transparency and surface color of composites.
What are PVC stabilizers? The role of PVC stabilizer
The action mechanism of PVC heat stabilizer
1) neutralize HCL and inhibit its autocatalytic effect. These stabilizers include lead salts, organic acid metal soaps, organotin compounds, epoxides, phenolic salts and metal mercaptan salts. They can react with HCL to inhibit the reaction of PVC HCL removal.
2) the substitution of unstable allyl chloride atoms in PVC molecules can inhibit PVC removal. For example, organotin stabilizers coordinate with the unstable chlorine atoms of PVC molecules, and organotin replaces the unstable chlorine atoms in the ligands.
3) addition reaction with polyene structure destroys the formation of large conjugated system and reduces coloring. Salts or esters of unsaturated acids contain double bonds, which react with conjugated double bonds in PVC molecule to produce diene adducts, thus destroying the conjugated structure and inhibiting discoloration.
4) capture free radicals and prevent oxidation reactions. For example, adding phenolic heat stabilizers can block the removal of HCL, because the H atom free radicals given by phenols can couple with the degraded PVC macromolecular free radicals to form substances that can not react with O2 and have thermal stabilization effect. This heat stabilizer can have one or both functions.
The ideal heat stabilizer for PVC should be a multi-functional substance or a mixture of some materials, which can achieve the following functions: first, to replace active and unstable substituents; second, to absorb and neutralize the HCL released during the processing of PVC to eliminate the autocatalytic degradation of HCL; third, to neutralize or passivate the catalytic degradation of HCL. Metal ions and other harmful impurities; Fourth, through a variety of chemical reactions can block the continued growth of unsaturated bonds, inhibit degradation coloring; Fifth, the best protection against ultraviolet light shielding. Usually, heat stabilizers are used in combination with each other according to their special efficacy, and seldom used alone. Most of them are powdery, some are highly toxic chemicals. In order to use conveniently, prevent dust poisoning, reduce toxic substances or replace them with non-toxic substances, many kinds of composite stabilizers have been developed at home and abroad in recent years. For example, the world-famous series of German Bear composite stabilizers, the United States, Germany, Japan, the Netherlands and other countries'organic tin or composite organic tin stabilizers, all occupy considerable cities in China. The field. Therefore, it is an urgent need for the development of plastics industry to popularize and apply the new composite stabilizer with high efficiency, low cost, no dust pollution, non-toxicity or low toxicity developed in China.
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