What types of PVC heat stabilizers are there?

Lead salt stabilizer

Lead salt stabilizers can be divided into three categories: (1) simple lead salt stabilizers, mostly salt-based salts containing PbO; (2) heat stabilizers with lubricating effects, mainly neutral and base groups of fatty acids Salts; (3) complex lead salt stabilizers, and solid and liquid composite stabilizers containing a synergistic mixture of lead salts and other stabilizers and components.

The lead salt stabilizer has strong thermal stability, good dielectric properties, and low price. The reasonable ratio of lubricant to PVC can widen the processing temperature range of PVC resin, and the quality of processed and post-processed products is stable. A commonly used stabilizer. Lead salt stabilizers are mainly used in hard products. Lead salt stabilizers have the characteristics of good heat stabilizer, excellent electrical properties and low cost. However, lead salts are toxic, cannot be used for products that come into contact with food, nor can they be made transparent, and are easily contaminated with sulfides to form black lead sulfide.

Metal soap stabilizer

Stearic acid soap heat stabilizers are generally prepared by saponification of alkaline earth metals (calcium, cadmium, zinc, antimony, etc.) with stearic acid, lauric acid, and the like. There are many types of products, each with its own characteristics. Generally, lubricious stearic acid is superior to lauric acid, and PVC compatible lauric acid is superior to stearic acid.

Because metal soap can absorb HCl, some varieties can also replace the Cl atom of the active site with the fatty acid root by the catalytic action of its metal ions, so it can exert different degrees of thermal stabilization on PVC. Very little in the PVC industry is a single metal soap compound, but usually a composite of several metal soaps. Commonly used are calcium zinc soap stabilizers. According to the Frye-horst mechanism, the stabilization mechanism of the calcium/zinc composite stabilizer can be considered as follows: first, the zinc soap reacts with the allyl chloride on the PVC chain, and then the calcium soap and the zinc soap react with the chlorine chloride to form an unstable metal chloride. At this time, the auxiliary stabilizer as an intermediate medium transfers the chlorine atoms to the calcium soap to regenerate the zinc soap, delaying the formation of zinc chloride having a function of promoting dehydrochlorination.

Calcium-zinc stabilizers can be used as non-toxic stabilizers in food packaging, medical devices, and pharmaceutical packaging, but their stability is relatively low. When the amount of calcium stabilizers is large, the transparency is poor and easy to spray. Calcium-zinc stabilizers generally use polyols and antioxidants to improve their performance. There are already transparent calcium-zinc composite stabilizers for hard pipes in China.

Organotin stabilizer

The alkyl tin in organotin is usually methyl, n-butyl or n-octyl. There are three main types of commonly used organotin stabilizers: (1) aliphatic acid salts, mainly refers to dibutyltin dilaurate, di-n-octyltin dilaurate, etc.; (2) maleate salts, mainly horses Dibutyltin acid, bis(monobutyl maleate) dibutyltin, di-n-octyl maleate, etc.; (3) thiolates, of which bis(thiocarboxylic acid) ester is the most used. Organotin-based heat stabilizers have good performance and are good varieties for PVC hard products and transparent products. Especially, octyl tin is an indispensable stabilizer for non-toxic packaging products, but its price is relatively expensive.

The organotin heat stabilizer (tinyl thioacetate) has a good stabilizing effect on PVC. Especially liquid organotin stabilizers, liquid organotin stabilizers can be better mixed with PVC resins than solid heat stabilizers. The organotin stabilizer (tinyl thioacetate) can replace the unstable Cl atoms on the polymer, giving the PVC resin long-term stability and initial color retention.

Rare earth stabilizer

Rare earth heat stabilizers mainly include organic weak acid salts and inorganic salts of light rare earth lanthanum, cerium and lanthanum. The types of organic weak acid salts are rare earth stearate, rare earth fatty acid, rare earth salicylic acid, rare earth citrate, rare earth lauric acid, rare earth octoate and the like.

The preliminary study on the mechanism of action of rare earth stabilizers is as follows: (1) The special electronic structure of rare earth lanthanides (8 electrons in the outermost layer, 8 electronic structures in the outer layer, and many empty orbits) Very small, under the action of external thermal oxygen or under the action of polar groups, the outer or secondary outer electrons are excited, can coordinate with the unstable Cl on the PVC chain, and can be decomposed with hydrogen chloride in PVC processing. The formation of a coordination complex, while having a strong attraction between the rare earth element and the chlorine element, can play a role in controlling the free chlorine element, thereby preventing or delaying the automatic oxidation chain reaction of hydrogen chloride and functioning as a heat stabilizer. (2) Rare earth multi-functional stabilizer can physically adsorb the oxygen in PVC processing and the ionic impurities contained in PVC itself, and enter the lattice hole of rare earth multifunctional stabilizer, avoiding their C-Cl bond to the mother. Shock vibration. Therefore, through the action of the rare earth multifunctional stabilizer, the activation energy of the PVC dehydrogenation can be improved, thereby delaying the thermal degradation of the PVC plastic. (3) A suitable anionic group in the rare earth compound can function to replace the allyl chloride atom on the PVC macromolecule, thereby eliminating the degradation weakness and achieving the purpose of stabilization. There are many domestic researches on rare earth stabilizers.

In general, the stability effect of rare earth heat stabilizers is better than that of metal soap stabilizers. It has good long-term heat stability and has a wide synergy effect with other kinds of stabilizers. It has good tolerance and is not affected. Sulfur pollution, stable storage, non-toxic and environmentally friendly advantages. In addition, the rare earth element has a unique coupling effect with CaCO3, and at the same time promotes the plasticizing effect of PVC, thereby increasing the amount of CaCO3, reducing the use of processing aid ACR, and effectively reducing the cost. The stabilizing effect of rare earth on polyvinyl chloride is characterized by its unique synergistic effect. The proper combination of rare earth with certain metals, ligands and co-stabilizers can greatly improve the stability.

Other stabilizers

Epoxy

Epoxy compounds such as epoxy soybean oil, epoxy linseed oil, epoxy tall oil, butyl stearyl stearate, and octyl ester are commonly used secondary heat stabilizers for polyvinyl chloride, and they are combined with the above stabilizers. It has high synergistic effect, light stability and non-toxicity. It is suitable for soft, especially soft FVC products exposed to sunlight. It is usually not used in hard PVC products, and its disadvantage is easy to seep out. .

Polyhydroxyl

Polyhydroxyl compounds such as pentaerythritol and xylitol have a certain thermal stability effect on PVC, and are commonly used as a secondary heat stabilizer for PVC.

other

Phosphite, β-diketone, dihydropyrimidine, etc. can be used as an auxiliary heat stabilizer for PVC to absorb the generated HCl and delay the discoloration of PVC.

At present, PVC heat stabilizers are developing towards non-toxic, low-toxic, compound and high-efficiency. Although China has made good progress in this respect in recent years, there is still a big gap compared with developed countries.