As one of the auxiliary additives used in PCV, heat stabilizer plays an indelible role in the modification of PVC products. The thermal stabilizer USES few fractions and has great effect, which can guarantee that PVC will not be decomposed during processing. The following are five kinds of thermal stabilizers, from classification to action mechanism, to show you a comprehensive understanding of thermal stabilizers.

Why use heat stabilizer?

          PVC during 100 ~ 150 ℃, ultraviolet light, mechanical force, oxygen, ozone, hydrogen chloride and some active metal salt and metal oxide will on the basis of its own decomposition to accelerate the decomposition speed.

            In the process of PVC processing, thermal decomposition has little change in its properties, mainly affecting the color of the finished product, and the addition of heat stabilizer can inhibit the initial coloring of the product. In addition, if there is oxygen in the thermal decomposition of PVC, there will be colloidal carbon, peroxide, carbonyl and ester base compounds.

So, in order to solve this phenomenon.

            Will need to add heat stabilizer in PVC processing process, so that it can be to a certain extent by unstable chlorine atoms to replace PVC, absorption hydrogen chloride, addition reaction with unsaturated parts such as way to suppress the degradation of PVC molecules.

The dithermal stabilizer was classified as 1 lead salt

Lead salt is the most commonly used thermal stabilizer for PVC, and its dosage can account for more than half of PVC thermal stabilizer.

Advantages: good thermal stability, long-term thermal stability, excellent electrical insulation, good weather resistance.

             Disadvantages: poor dispersion, large toxicity, initial coloration, difficult to obtain transparent products, and difficult to obtain bright colors of products, lack of lubricity, to produce sulfur, separation pollution.

Type of lead salt stabilizer:

         Tribasic lead sulfate, molecular formula: 3PbO·PbSO4·H2O, code TLS, white powder, density 6.4g/cm cubed. It is commonly used with dibasic lead phosphates, and is lubricated with no lubrication. Mainly used in PVC hard opaque products, the dosage is generally 2~7.

        Lead 2-base phosphoric acid, molecular formula: 2PbO·PbHPO3· 1/2h2o, codendum DL, white powder, density 6.1g/cm cubed. Its thermal stability is slightly less than tribasic lead sulfate, but the weatherability is good. It is often used with tribasic lead sulfate, and the dosage is usually about half of the tribasic lead sulfate.

         Dibasic stearate lead, codendum DLS, is not as common as tribasic lead sulfate and dibasic lead phosphite, which is lubricious. It is often used with tribasic lead sulfate and dibasic phosphoric acid, and the dosage is 0.5~1.5.

          In order to prevent the toxic powdery lead salt stabilizer dispersing, seriously pollute the production environment and improve the dispersing effect of stabilizer, the dust - free composite lead salt thermal stabilizer has been developed. Its manufacturing process is:

          Various lead salt stabilizers, auxiliary heat stabilizers and internal and external lubricants with synergistic effect will be prepared in the heating and mixing conditions to make granular or flake lead salt composite stabilizers. By adding it to PVC resin (no other stabilizer and lubricant), it can achieve the technical requirements of thermal stability and internal and external lubrication.

            It is introduced that the lead salt stabilizer is made of lead-free lead salt stabilizer, and the surface area of the reaction with hydrogen chloride is increased. And because of the combination with internal and external lubricants, the dispersibility is good, the thermal stability efficiency is obviously increased, and the dosage can be reduced.

2 metal soap

             Dosage of the categories of the main second only to their lead salt stabilizer, its thermal stability is not lead salts, but also lubrication, in addition to the Cd and Pb are non-toxic, except Pb and Ca are transparent, no sulfide pollution, which is widely used in soft PVC, such as non-toxic, transparent, etc. Metal soap can be a fatty acids (lauric acid, stearic acid, naphthenic acid, etc.) of the metal (lead, barium, cadmium, zinc, calcium, etc.) of salt, among them the most commonly used with stearic acid salt, the thermal stability of size order for: > > > cadmium zinc salt salt of lead salt/barium salt, calcium salt. Metal soap is generally not used alone, often between metal soap classes, or with lead salt and organic tin.

Type of metal soap stabilizer:

Zinc stearate (ZnSt), non - toxic and transparent, can easily cause "zinc burn", often with Ba, Ca soap.

Cadmium stearate (CdSt) is an important type of transparent stabilizer, which is highly toxic, resistant to vulcanization, and often used with Ba soap.

Lead stearate (PbSt), good thermal stability, can be used as lubricant. The defect is easy to be precipitated, transparent, toxic and sulfide pollution is serious, often with Ba, Cd soap.

Calcium stearate (CaSt), good processing, no sulfide pollution, transparent, often with Zn soap.

BaSt, non - toxic, anti - sulphur pollution, transparent, often with Pb, Ca soap.

Lead stearate/CD/barium heat stabilizer.

The results showed that the thermal stability of lead stearate was good, but the amount of lead was decreased, and the transparency of PVC products was decreased.

            In addition, cadmium stearate not only has good thermal stability, but also has high transparency of PVC products. But cadmium stearate replacement PVC molecules generated after unstable chlorine atom RCOOCdCl continue to react with PVC on unstable chlorine atoms, the generated CdCl2 on PVC C - Cl health activation, to take off the HCl have a catalytic role.

Barium stearate was not only able to react with the extraneous HCl, but also regenerated cadmium stearate with CdCl2 reaction.

                 Therefore, lead stearate, septum and barium can be used to enhance the thermal stability of PVC and the transparency of PVC products. At present, the soft PVC calender is mainly used for the thermal stabilization system of lead, cadmium, barium and some epoxy compound and phosphatide.

Calcium stearate/zinc composite heat stabilizer.

          Calcium stearate, zinc non-toxic heat stabilizer, low price, suitable for food packaging PVC products. The results show that the ionization potential of zinc soap stabilizer is high, and the reaction of allyl chloride in PVC can stabilize the PVC and inhibit the initial coloring effect.

         In general, calcium stearate, zinc stearate, epoxy soybean oleate mainly composed of non-toxic compound heat stabilizer. It is worth to pay attention to that the new type of auxiliary heat stabilizer, which is used as a stabilizer of calcium and zinc, promotes the expansion of non-toxic calcium and zinc compound stabilizers. It is used in some food packaging materials such as PVC bottle and sheet.

3 organic tin

             Organic tin is the most effective and the most widely used type of thermal stabilizer. Its outstanding advantages are: high thermal stability, good transparency, and mostly non-toxic. The disadvantage is that the price is high (but the quantity is small, generally only 0.5~2 copies), and the other one is mostly non-lubricity.

Organic tin is mostly liquid and only a few are solid. Can be used alone, and often with metal soap.

Type of organic tin stabilizer:

             Sulfur organic tin is mainly composed of thiol organic tin and organic tin sulfide, such stabilizer and Pb, Cd soap and can produce sulfur pollution. The sulfur organic tin is transparent. The main varieties are:

          (1) isooctyl dithioglycid (DOTTG), with a light yellow liquid, excellent thermal stability and transparency, non-toxic, and less than 2 doses.

           (2) dimethyl dimercaptoacetate tin (DMTTG), with a pale yellow clarifying liquid, is a non-toxic, efficient and transparent stabilizer, often used in torsion and transparent film.

           (3) in addition to the above two types, there are also dibutyltin, dithioacetate-dibutyltin dibutyltin, dithioglycipionate, and dioxin.

Organic tin carboxylic acid salt, the stability of this stabilizer is less than the sulfur organic tin, but no sulfur pollution, mainly including the fatty acid tin salt and the maleate tin salt. The main varieties are:

    (1) di-n-butyltin (DBTL), light yellow liquid or semi-solid, good lubricity, good transparency, but toxic, often used with Ba and Cd soap, dosage 1~2 parts; With tin and tin of maleate and tin, the dosage is 0.3~1.

  (2) diazoic acid (DOTL), toxic and high price, good lubrication, used in hard PVC, with less than 1.5 portions.

  (3) maleic acid di-butyl tin (DBTM), white powder, toxic, non-lubricious, often used with the lauric acid tin, not with metal soap and used in transparent products.

（4）organic antimony class this is a new type of PVC heat stabilizer, it has good initial color and color retention, especially in low dosage, the thermal stability is better than that of organic tin, especially suitable for PVC formulations used in twin screw extruder.

Type of organic antimony stabilizer:

Sulphide antimony salt.

Sulfhydryl acetate sulfide antimony class.

Sulfhydryl carboxylate antimony and carboxylate antimony class.

                     Domestic antimony stabilizer is mainly in three thioglycolic acid diisooctyl antimony (ST) and ST as the main component of composite stabilizer STH - Ⅰ and STH - Ⅱ two primarily. It is a transparent liquid, which can be used as a heat stabilizer for transparent films, films and transparent granules. STH - Ⅰ tin can replace Beijing C - 102, inhibits the early stages of the PVC color, good thermal stability, product transparent, bright color. STH - Ⅱ non-toxic, mainly used for PVC pipe and other products.

5 rare earth stabilizer

                     The stabilizer is a unique stabilizer developed by China and is a new type of thermal stabilizer. The rare earth elements include 15 lanthanide elements from 57 to 71 and 17 elements like yttrium and thorium.

Type of rare earth stabilizer:

Rare earth oxides and hydroxides.

Rare earth organic weak acid salts (such as stearic acid rare earth, fatty acid rare earth, salicylic acid rare earth, citric acid rare earth, tartaric acid rare earth and malate rare earth etc.)

Among them, rare earth hydroxide has the best thermal stability, and rare earth organic acid is better than rare earth.

             The thermal stability of rare earth stabilizer is comparable to that of jingsi-8831, which is better than lead salt and metal soap, which is three times as much as lead salt and four times as much as Ba/Zn compound stabilizer. It is non-toxic, transparent and cheap. It can be widely used to replace the organic tin stabilizer. The rare earth stabilizer is not lubricated and should be added with lubricant. The amount of rare earth stabilizer is about 3.

               SR series of rare earth composite thermal stabilizers (including external lubricants, auxiliary thermal stabilizers, etc.) are classified into two categories: A and B, which are suitable for hard PVC pipes and profiles. The reference formula is as follows:

Name of raw material

Formula addition

PVC

100

CPE

2 ~ 4

ACR

0.5 ~ 2

Other modifier

2 ~ 4

CaCO3

8

Rare earth compound stabilizer (sr-g) (A and B)

8 ~ 12

Mixing order: PVC+CPE+A package stabilizer, ACR+B package stabilizer.

Rare earth stabilizer commonly used part number:

brand

application

REC - 259 - a, 259 b

Hard PVC upper pipe

REC - 258.

Injection molding hard PVC pipe fittings.

REC - 408 - a, 408 b

Soft PVC rolled film.

REC - 851 - b

Food grade hard PVC transparent rolling sheet.

REC - 859.

PVC mineral water bottle

Liquid complex thermal stabilizer.

The liquid composite heat stabilizer consists of organic metal soap, phosphatide, hindered phenol antioxidant and solvent. 

Organic metal soap is the main component of liquid compound stabilizer.

Composition of liquid composite thermal stabilizer:

Metal soap has cadmium/barium/zinc, barium/zinc, calcium/zinc, etc.

Organic acids have acid, oleic acid, naphthenic acid, synthetic fatty acid, benzoic acid, salicylic acid and so on.

The mixed phosphite is triphenyl phosphite, diisooctyl phosphite, bisphenol A diphosphatate (pl-40) and oligomer (pl-440).

Commonly used antioxidants are bisphenol A or hindered phenol antioxidant.

The solvent is plasticizer, advanced alcohol, advanced alkanes and so on.

                The main products are liquid barium/cadmium/zinc, barium/cadmium, calcium/zinc, barium/zinc and other compound stabilizers, respectively used in soft PVC calendering film, hard PVC transparent sheet, PVC transparent bottle, etc.

Pure organic heat stabilizer.

           Non-metallic organic heat stabilizer, amino crotonic acid ester, such as beta 2 - phenyl indole, 3 phenyl urea, etc., was used as the main non-toxic stabilizers, but its high temperature resistance, long-term heat resistance, light fastness is poorer, is now rarely used.

In recent years, according to the requirements of environmental friendly and non-toxic and harmless, the research on pure organic heat stabilizer without metal has achieved good results.

          For example, Ciba precision company developed an organic heterocyclic thermal stabilizer with amine pyrimidine dione ring as the core, which is used for extrusion of hard PVC tube. The thermal stability of lead salt stabilizer can be achieved. For example, the pure organic heat stabilizer developed by Morton company with active organic sulphide can replace the cadmium system and Ba/Zn, Ca/Zn thermal stability system in the processing of soft PVC products.