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Chemical knowledge

A Brief Introduction of PVC Heat Stabilizers

2014/11/20

PVC main heat stabilizers refer to those compounds with stabilizing effect when they are used alone. While assistant stabilizers are those compounds which is invalid when use them alone, but having synergistic effect when used in combination with main stabilizers. There are synergistic effects between some main stabilizers or some main and assistant stabilizers after choosing to use.

1. Basic Lead Salt

Basic lead salt is the earliest and most widely used heat stabilizer for PVC. It shows basicity, so it can react with HCL which is produced by PVC under high temperature, thus it owns its stabilizing effect. Seen from virulence, stain resistance and product transparency, lead salt is not ideal. But with its good stabilizing effect and low cost, it is still massively used in cheap PVC extrusion and rolled products. With its good electrical property and low moisture uptake, it is widely used as PVC electrical insulation products, records and the stabilizer of foamed plastic.

1.1 Lead Sulfate Tribasic (Also known as tribasic lead sulfate)

This is white powder with the proportion of 7.10, sweet, poisonous, easy to absorb moisture, non-flammable, non-corrosive, insoluble in water but soluble in hot ammonium acetate. It will discolor and decompose after exposing to light when it is moist. The refractive index is 2.1. It is usually used as the stabilizer of electrical isolation products.

1.2 Dibasic Lead Phosphite

This is tiny needle-like acicular crystal with the proportion of 6.1, sweet, poisonous. When it is about 200℃, it turns into cinereus, and if it is about 450℃, it turns into yellow. It is insoluble in water and organic solvent but soluble in hydrochloric acid. The refractive index is 2.25. Having the effect of antioxidant, it is a good weather resisting stabilizer.

2. Metallic Soap

Metallic soap is also one kind of widely used heat stabilizer of PVC. Simple substance or mixture of barium carboxylic acid, cadmium carboxylic acid, zinc carboxylic acid, calcium carboxylic acid are used. Its stabilizing effect is due to the esterification at where PVC molecular chain begins to decompose. The strength of stabilizing effect is related to metal ratio in metallic soap, the type of carboxylic acid and exsisting phosphate ester, cyclo-oxidized oil, antioxygen and other synergist in the formula or not. Among them cadmium soaps and zinc soaps have the greatest stabilizing effects.

2.1 Lead Stearate

This is a kind of fine powder, insoluble in water, soluble in hot ethyl alcohol and diethyl ether. It become to glue after cooled when being heated in the organic solvent. It is hydroscopic and decomposes into stearic acid and corresponding lead salt when meeting strong acid. Good unctuosity and low melting point ensure its good dispersity.

2.2 Diethyl Lead Acetate

It is soluble in solvent and plasticizer. It is usually processed into 57-60% mineral oil or solution of plasticizer for sale and widely used as activator of azodicarbonamide-the foaming agent of foamed plastic.

2.3 Lead Protection Salicylate

This is a kind of white crystal powder with the proportion of 2.36, the refractive index of 1.76. It has effects of PVC heat stabilizer and light stabilizer.

2.4 Tribasic Lead Stearate

This is a kind of white powder with the proportion of 2.15. Decompose at 280-300℃ and easily cake over100℃. It is soluble in diethyl ether, poisonous, non-flammable and non-corrosive, with the refractive index of 1.60. With good unctuosity and fine light stability, it is widely used for PVC record formula.

2.5 Dibasic Lead Phthalate

This is a kind of white fine powder with the proportion of 4.5, a weak acid, insoluble in ordinary solvents. Its base is easy to be carbonated. Its refractive index is 1.99. If there are plasticizers which tend to saponify in the formula, the stabilizing effect of dibasic lead phthalate is superior to that of trisalty lead sulfate.

2.6 Tribasic Lead Maleic Acid

This is fine yellow powder, with the proportion of 6.0, the refractive index of 2.08, poisonous, non-flammable and non-corrosive. It has good color stability and wipe out unstable diene stucture.

2.7 Barium Stearate

This is white fine powder with the barium content of 19.5-20.6%, the proportion of 1.145, the melting point of 225℃ above, insoluble in water, soluble in hot ethyl alcohol. It become to glue after cooled when being heated in the organic solvent. It is hydroscopic and decomposes into stearic acid and corresponding barium salt when meeting strong acid. It is recommended heat stabilizer when sulful pollution must be avoided and lubricant adopt in high temperature processing.

2.8 Barium Cinnamate

2.9 Barium Ricinoleate

This is yellowish white powder with the melting point of 116-124℃, the stabilizer being able to make products get good transparency.

2.10 Cadmium Stearate

This is white fine powder wit cadmium content of 16.5-17.5%, insoluble in water, soluble in hot ethyl alcohol. It become to glue after cooled when being heated in the organic solvent. It is hydroscopic and decomposes into stearic acid and corresponding cadmium salt when meeting strong acid. It is PVC heat and light stabilizer required to have good transparency.

2.11 Cadmium Ricinoleate

This is a kind of white powder with the melting point of 96-104℃, having effects of heat and light stabilizer.

2.12 Calcium Stearate

This is white fine powder, insoluble in water, soluble in hot ethyl alcohol and diethyl ether. It is hydroscopic and decomposes into stearic acid and corresponding calcium salt when meeting strong acid. Acting as non-poisonous PVC stabilizer and lubricant, it is usually used cooperatively with zinc soaps, magnesium soaps or epoxy assistant stabilizer.

2.13 Calcium Ricinoleate

This is white powder with the melting point of 74-82℃, non-poisonous PVC stabilizer.

2.14 Zinc Stearate

This is white fine powder, insoluble in water, soluble in hot ethyl alcohol, turpentine, benzene and other organic solvents. It become to glue after cooled when being heated in the organic solvent. It is hydroscopic and decomposes into stearic acid and corresponding zinc salt when meeting strong acid. It is non-poisonous PVC stabilizer and lubricant.

2.15 Magnesium Stearate

This is white powder with the proportion of 1.07, 85℃ melting point of sterling products, 108-115℃ melting point of industrial products. It is slightly soluble in water, soluble in hot ethyl alcohol. It decomposes into stearic acid and corresponding magnesium salt when meeting strong acid. Being one kind of non-poisonous PVC stabilizer and lubricant, it is also the lubricant of phenolic aldehyde and urea resin.

3. Compound Stabilizer

3.1 Cadmium Barium Liquid and Zinc Cadmium Barium Liquid Compound Stabilizer

This kind of compound stabilizers is used in processing soft PVC products. The basic components include:

(1) Barium salt-it can be barium alkylphenol, diethyl barium caproate, barium laurate, benzoic acid and replace barium benzoate, and barium neodecanoate and so on. Barium salt accounts for 6-7% of the compounds and the ratio of barium salt and cadmium salt is 2: 1.32 (counted by metal, weight percentage, the same below).

(2) Cadmium salt-it can be diethyl cadmium caproate, cadmium laurate, cadmium oleate, phenyl acid and replace cadmium benzoate, cadmium naphthenate, cadmium neodecanoate and so on. Cadmium salt accounts for 3-4% of the compounds.

(3) Zinc salt- it can be diethyl zinc caproate, zinc laurate, zinc naphthenate, zinc neodecanoate, benzoic acid and replace zinc benzoate and so on. Zinc salt accounts for 0.5-1% of the compounds.

(4) Phosphate ester-it can be triphenyl phosphate, DPOP, decyl diphenyl phosphate, Phenol, 4-nonyl-, phosphite (3:1) and so on. Phosphate ester accounts for 15-20% (weight) of the compounds, acting as chelating agent.

(5) Others-includes little 2,6-ditertbutylpcresol, BPA, nonylphenol and other Phenolic antioxygens and ultraviolet light absorber, liquid paraffin, white oil, diesel, spindle oil and other mineral oil acting as solvents. Besides, a small amount of higher alcohol and other defoaming agents must be added in.

Zinc cadmium barium liquid compound stabilizers with different constitutes have different properties. But they are usually pale yellow to yellow clear liquids with the proportion of 0.95-1.02 at room temperature. Their viscosity is less than 100cp and their freezing point is about －15℃. Liquid cadmium barium is similar to liquid zinc cadmium barium, both of which have good light and heat stability, little initial coloration, favourable transparency and color stability. Compared with solid soaps, they have stronger stabilization. So their dosage can be reduced, usually 2-3phr and dust poisoning never happened. They are also completely soluble in ordinary plasticizers with good dispersity and fewer precipitation tendencies. Among them the initial coloration of liquid zinc cadmium barium is less than that of liquid cadmium barium.

3.2 Zinc Barium Liquid Compound

It is usually pale yellow to yellowish-brown oily liquid with the proportion of 1.0-1.1 at room temperature, good heat resistance, sulfide pollution resistance. Used with epoxy plasticizer can improve stabilizing effects. Besides, it has an activating effect on foaming agent.

3.3 Zinc-calcium Liquid Compound

The major ingredients of non-poisonous zinc calcium liquid stabilizer are calcium stearate, calcium ricinoleate, zinc srearate, zinc ricinoleate, epoxidized soybean oil, ultraviolet light absorber and so on. Zinc calcium liquid stabilizer generally uses fatty acid calcium and zinc salt which are comparatively soluble in organic solvents and have less carbon numbers. Because of their different constitutes, they have different properties. They are usually pale yellow to yellow clear oily liquids with the proportion of 1.0-1.05 at room temperature. As non-poisonous PVC stabilizer, they can also be used as food packaging film, vessel and the stabilizer of foamed synthetic leather.

4. Organic Tin Stabilizer

Organic tin stabilizer is the ramification of various organotin-carboxylate and stannum mercaptide. Its main products are DBT and dioctyltin organic compounds among which dioctyltin organic compounds are used as non-poisonous stabilizers by more counties. Organotin is mainly used to stabilize rigid PVC products, especially those with the requirements of good transparency and heat stabilization. Of course, it can also stabilize soft products, but it is generally not used because of its higher price.

This is a kind of faint yellow clear liquids, poisonous and soluble in all industrial plasticizers and solvents. It is the oldest species in organotin with good unctuosity, transparency, weather fastness, sulphur pollution resistance while bad heat resistance. It is used as the main stabilizer of soft transparency products and the lubricant of rigid transparency products.

4.2 Dibutyltin Maleate

This is a kind of white armorphous powder. Its melting point and volatility change with the degree of polymerization during 100-140℃. It is poisonous with tearing property, mainly used in rigid transparency products required to have high softening point and impact strength. It is used with dibutyltin dilaurate with the dosage of 0.5-2phr for lack of lubrication.

4.3 Di-n-butyltin (Monobutyl maleate)

This is faint yellow transparency liquid, non-poisonous (less than 3phr is allowed). This product has good weather fastness, transparency, heat stability, preventing colorability and the sulphur pollution never happened. It is usually used for transparency rigid PVC products with the dosage of 2.0-4.0 phr.

4.4 Di-n-octyltin (Iso-octyl mercaptoacetate)

This is faint yellow liquid, unsoluble in water, soluble in ester, ether, alcohol, aliphatic hydrocarbon, arene and main types of plasticizer. It is the main species of stannum mercaptide and one of the most commonly used non-poisonous stabilizer of organotin. It is used for rigid transparency PVC (2-3phr) and soft transparency PVC (1phr). While there are some defects: bad weather fastness, frowziness, sulphur pollution, lack of lubrication. Besides, it has certain plasticization thanks to the ester group.

4.5 Dioctyldilauryltin

This is a kind of yellow liquid with the proportion of 1.01-1.02 at 25℃, the refractive index of 1.46-1.47. Its viscosity is less than 60cp at 30℃. It is non-poisonous with good lubricity and mainly used for food packaging material of rigid transparency PVC with less than 1.5phr dosage.

4.6 Di-n-octyltin Moleate

This is a kind of white powder with the melting point of 87-105℃, insoluble in water, soluble in benzene, alcohol and acetone, excellent long-term heat resistance. It is non-poisonous and mainly used as the assistant stabilizer of stannum mercaptide with the dosage of 0.3-0.5phr.

5. Assistant Heat Stabilizer

5.1 Epoxy Compound

Epoxidized soybean oil, epoxidized linseed oil, epoxidized tall oil, epoxidized butyl stearate, 2-ethylhexyl epoxystearate and other epoxy compounds are commonly used as the assistant heat stabilizers of PVC. Used cooperatively with main stabilizers above, they can create significant synergistic effect. With advantages of light stability and no poison, they apply to soft products, especially those soft PVC products exposed to sunlight, while they are usually not used for rigid PVC products.

5.2 Phosphite Ester

DPDP and PDDP are also assistant heat stabilizers of PVC. Especially used in baric/cadmiferous/calciferous/zinciferous stabilizer system, they can improve product transparency. Because of their hydrolytic property, they cannot be used as assistant stabilizer for those PVC products which must contact with water.

5.3 Other Organic Compounds

Used with main heat stabilizers, diphenylsulfourea, 2-Phenylindole, β-ethylenedicarboxylic acid and ester, trimethylolpropane , sulfo-lauric anhydride, other polyhydric alcohols with high boiling points, such as pentaerythritol, sorbitol, mannitol and so on, can also develop synergism.