Action mechanism and application of different PVC stabilizers

PVC stabilizers, especially heat stabilizers in PVC stabilizers, have a wide range of uses and many types. Such as lead salt composite stabilizer, organotin stabilizer, calcium zinc composite stabilizer, liquid composite stabilizer, barium zinc composite stabilizer, potassium zinc composite stabilizer, etc.
[Thermal stability mechanism of PVC stabilizer] 1. Absorb hydrogen chloride Me (OOCR) 2+2HCl==MeCl2+2HOOCR where Me is Pb, Ba, Cd, Ca, Zn, Sn, Sb, Mg, Sr, etc. 2. Eliminate unstable chlorine atoms to replace or eliminate unstable chlorine atoms. 3. It can prevent the auto-oxidized PVC from being easily degraded by O2 oxidation under the action of thermal oxygen and shear force. 4. Adding metal salts of maleic acid can inhibit or eliminate double bonds or make them shorter or less.
[Characteristics and application of several PVC stabilizers]
1、 Lead salt composite stabilizer The lead salt composite stabilizer has strong thermal stability, good dielectric properties, and low price. The reasonable ratio with lubricant can make the processing temperature range of PVC resin wider, and the quality of processed and post-processed products is stable. It is the most commonly used stabilizer at present. Lead salt stabilizer is mainly used in hard products. Lead salt stabilizer has the characteristics of good heat stabilizer, excellent electrical performance and low price. However, lead salt is toxic and can not be used in products that contact with food, nor can it make transparent products, and it is easy to be contaminated by sulfide to generate black lead sulfide.
2、 Calcium and zinc composite stabilizers Calcium and zinc composite stabilizers can be used as non-toxic stabilizers in food packaging, medical devices and drug packaging, but their stability is relatively low. When calcium stabilizers are used in large amounts, their transparency is poor and they are easy to spray frost. Calcium and zinc stabilizers generally use polyols and antioxidants to improve their performance. In recent years, domestic environmental protection requirements are becoming more and more stringent, and calcium and zinc composite stabilizers are widely emerging in full swing.
3、 The alkyl tin in organotin stabilizer is usually methyl, n-butyl and n-octyl. Most of the products produced in Japan are butyl tin, and octyl tin is more common in Europe. This is the standard non-toxic stabilizer approved in Europe, while methyl tin is used more in the United States. There are three main types of organotin stabilizers commonly used: 1. Aliphatic acid salts, mainly dibutyltin dilaurate, di-n-octyltin dilaurate, etc; 2. Maleate salts mainly refer to dibutyltin maleate, bis (monobutyl maleate) dibutyltin maleate, di-n-octyltin maleate, etc; 3. Mercaptans, of which bis (thiocarboxylic acid) ester is the most used. Organotin heat stabilizer has good performance and is a good variety for PVC hard products and transparent products. In particular, octyltin has almost become an indispensable stabilizer for non-toxic packaging products, but its price is relatively expensive. Organic tin heat stabilizer (tin mercaptoacetate) has a good stabilizing effect on PVC. Especially the liquid organotin stabilizer can be better mixed with PVC resin than the solid heat stabilizer. The organotin stabilizer (tin mercaptoacetate) can replace the unstable Cl atoms on the polymer, making the PVC resin have long-term stability and initial color retention. The stabilization mechanism of tin mercaptoacetate is proposed as follows: 1) S atom can replace unstable Cl atom, thus inhibiting the formation of conjugated polyolefins. 2) As a product of PVC thermal degradation, HCl can also accelerate the formation of conjugated polyolefins. Tin mercaptoacetate can absorb the HCl produced.

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