Current situation and development analysis of the

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The main function of heat stabilizer is to prevent or inhibit the thermal decomposition of PVC resin in the processing process and prolong the service life of products. At present, the commonly used PVC heat stabilizers can be divided into four categories according to their chemical composition: lead salts, metal soaps, organic tin and composite stabilizers

(1) lead salt lead salt stabilizer is mainly used to combine HCl released during PVC degradation to produce stable lead chloride, which is suitable for manufacturing opaque products. Lead salt stabilizer is widely used because of its high thermal stability, good electrical insulation, low water absorption and low price. The main varieties of lead salt heat stabilizers are "three salts" and "two salts". "Three salts" have high thermal stability efficiency, good electrical insulation and high coverage; The disadvantage is that it has no lubricity and poor dispersion, so lubricant should be added in the formula. "Two salt" has outstanding weather resistance, strong oxidation resistance and UV shielding ability, and is an essential stabilizer in outdoor PVC products; The disadvantage is that the heat resistance is not as good as "three salts". When the temperature exceeds 200 ℃, several ways to avoid mice are introduced to users below "two salts": "it is easy to decompose, so it is not suitable for occasions with high processing temperature

(2) metal soaps metal soaps can not only react with HCI, but also replace the unstable chlorine atoms on the PVC molecular chain. They are a kind of heat stabilizer with lubricating effect. Metal soaps have sufficient heat resistance, most of them are non-toxic or low toxic, only a few will be affected by sulfides, and most of them can be used for translucent products. The main metal soap heat stabilizers include lead stearate, barium stearate, cadmium stearate, etc. lead stearate has good thermal stability, good lubricity and good light resistance, but it is easy to be polluted by sulfide, and should not be used in transparent products, and the dosage should not be too much, generally about 1 part

(3) organotin organotin heat stabilizer has good stability. It can be used alone or in combination with other soaps. Its transparency is good, and extremely low precipitation will not cause scaling. Therefore, organotin stabilizer is one of the main stabilizers of PVC. Organotin stabilizers have excellent light and heat stability, resistance to initial coloring, high transparency and non-toxic or low toxicity. They are ideal heat stabilizers for PVC food, drug packaging, blow molding bottles and drinking water pipes widely used in the construction of steel deep processing bases in the world. However, the price of organotin heat stabilizers is on the high side, and some products have unpleasant smell, which limits their application to a certain extent

(4) composite stabilizers currently used are mainly made of barium, cadmium, calcium, zinc and other metal soaps and salts, together with phosphite. Barium has good thermal stability. When it is used to stabilize PVC, zinc soap is first replaced with allyl chloride and consumed. The generated zinc chloride transfers chlorine to barium soap and receives carboxylic acid to generate zinc soap. The composite stabilizer can give profile products good aging resistance and thermal stability, without sulfide pollution, and is suitable for the selection of outdoor building materials. However, due to its toxicity, the amount of cadmium salt has been reduced, and even banned in some countries

in a word, according to the current situation, experts have done a lot of research work on the stabilizer of PVC. The most mature are the lead salt system stabilizer and the expensive organotin stabilizer that have been used at home and abroad. However, the toxicity of lead salt, the one-way transmission characteristics of worm gear reducer 3 and the expensive and peculiar smell of organotin are the fatal defects of these stabilizers. Therefore, experts have been constantly discussing and studying for many years, hoping to find a non-toxic and affordable high-efficiency stabilizer

in recent years, experts have found that light rare earth organic compounds have a series of special chemical and physical properties and can combine with a variety of organic coordination molecules. The rare earth stabilizer for PVC processing (REC) obtained by complexing light rare earth cations with one or several anion groups whose anion separation temperature cannot be higher than 150 degrees or adding synergistic substances to it has excellent thermal stability for PVC

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