PVC stabilizers, especially heat stabilizers in PVC stabilizers have a wide range of uses and many types. Such as: lead salt composite stabilizer, organic tin 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
Among them, 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. Prevent auto-oxidizing PVC from being easily degraded by O2 oxidation under the action of hot oxygen and shearing force.
4. Adding the metal salt of maleic acid can inhibit or eliminate the double bond or make it shorter or less.
[Features and applications 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 of the lubricant can widen the processing temperature range of PVC resin, and the quality of processed and post-processed products is stable. The most commonly used stabilizer. Lead salt stabilizers are mainly used in hard products. Lead salt stabilizers have the characteristics of good thermal stabilizers, excellent electrical properties, and low price. However, lead salt is toxic and cannot be used in food-contact products, nor can it be made transparent, and it is easily contaminated by sulfide to generate black lead sulfide.
2. Calcium and zinc compound stabilizer
The calcium-zinc composite stabilizer can be used as a non-toxic stabilizer for food packaging, medical equipment, and pharmaceutical packaging, but its stability is relatively low. When the calcium stabilizer is used in a large amount, the transparency is poor and it is easy to bloom. Calcium-zinc stabilizers generally use polyols and antioxidants to improve their performance. In recent years, domestic environmental protection requirements have become stricter, and calcium-zinc composite stabilizers are in full swing.
3. Organotin stabilizer
The alkyl tin in organotin 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 a standard non-toxic stabilizer recognized in Europe, and methyl tin is used more in the United States.
There are three commonly used organotin stabilizers:
1. Aliphatic acid salts, mainly refer to dibutyl tin dilaurate, di-n-octyl tin dilaurate, etc.;
2. Maleates, mainly refer to dibutyl tin maleate, bis(monobutyl maleate) dibutyl tin, di-n-octyl tin maleate, etc.;
3. Mercaptides, of which bis(thiocarboxylic acid) esters are the most used.
Organotin heat stabilizers have good performance and are 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 thioglycolate) has a good stabilizing effect on PVC. Especially the liquid organotin stabilizer, compared with the solid heat stabilizer, the liquid organotin stabilizer can be better mixed with PVC resin. The organotin stabilizer (tin thioglycolate) can replace the unstable Cl atom on the polymer, so that the PVC resin has long-term stability and initial color retention. The stabilization mechanism of tin thioglycolate is proposed: 1) S atoms can replace unstable Cl atoms, thus inhibiting the formation of conjugated polyolefins. 2) As a product of thermal degradation of PVC, HCl can accelerate the formation of conjugated polyolefins. The tin thioglycolate can absorb the generated HCl.