The article reads the type, problem and requirement of foaming agent

Blowing agent type

According to different gas generation methods, foaming agents can be divided into physical foaming agents and chemical foaming agents.

Foam plastic

Physical blowing agent

The physical foaming agent mainly forms the cells in the plastic through the change of the physical state of the foaming agent.

The ideal physical foaming agent should have the following conditions:

1 inert, non-toxic;

2 and resin compatible;

3 The diffusion rate in the resin matrix is ​​small;

4 When the resin reacts to give off heat, or when it is heated externally, it should be easy to volatilize.

In general, physical foaming agents fall into three categories: 1 Compressed gas; 2 Soluble solids; 3 Volatile liquids with boiling points below 0°C.

During processing, when the pressure is relieved, the compressed gas expands, or the liquid evaporates and expands by heat, or the dissolved soluble solid material sublimates to generate gas.

The commonly used volatile blowing agents are: aliphatic hydrocarbons containing 5 to 7 carbons; halogenated hydrocarbons; low-boiling alcohols, ethers, ketones, and aromatic hydrocarbons. The engineering plastics that usually use physical foaming agents include ABS and phenolic resins.

(1) Carbon dioxide blowing agent

One is the reaction of isocyanate with water to produce carbon dioxide (water foaming) as a blowing agent and the other is liquid carbon dioxide.

At present, it is mainly used in heat pipe insulation, packaging foam plastics and agricultural foam plastics, etc., which are not required for heat insulation. The advantages and disadvantages of liquid carbon dioxide foaming are the same as those of water foaming. Currently, they are mainly used for polyurethane foams.

(2) Hydrogen chlorofluorocarbon (HCFC) foaming agent

Hydrogen is contained in the molecule and its chemical properties are unstable. It is relatively easy to decompose.

The most mature product currently commercially available to replace CFC-11 is HCFC-14LB, which has good compatibility with polyols and isocyanates. It can be directly replaced with HCFC-14LB instead of CFC-11 under the condition that no equipment is added, and the same density can be achieved. The physical properties of the foam are similar to those of CFC-11. The disadvantage of HCFC-141B is its high raw material price, its solubility in some ABS and high impact polystyrene, and its higher thermal conductivity than CFC-11. Therefore, it is necessary to obtain a higher density foam to achieve Thermal insulation effect.

(3) Hydrocarbon blowing agent

The hydrocarbon compound used for the polyurethane foaming agent is mainly cyclopentane, and particularly a rigid foam system of cyclopentane has the advantages of low thermal conductivity, aging resistance, zero ODP value, etc., and is often used in refrigerators, cold storages, and refrigerators. The thermal insulation and other fields of construction have become the first choice for China's hard foam CFC-11 substitutes.

(4)Hydrofluoroalkane (HFC) blowing agent

HFCs have a zero ODP value and are ideal substitutes for CFC-11 in the production of soft PU foams. Early HFC-based foaming agents were mainly HFC-134A and HFC-152A. These two blowing agents have low molecular weight. With the low boiling point, when the foams with the same density and similar physical properties are used, the dosage is less than that of CFC-11, and the performance is relatively stable, but their defects are that the thermal conductivity is relatively high, and the solubility in common polyols is low. It is relatively difficult to process composite polyethers containing HFC-134A and HFC-152A. In addition, foaming equipment is required to meet the processing requirements.

Chemical foaming agent

Chemical foaming agent is also called decomposing foaming agent. They can be uniformly dispersed in the resin and decomposed by heat to produce at least one gas. Can be divided into inorganic foaming agents and organic foaming agents. Organic foaming agents are the main blowing agents used in plastics, mainly azo, nitroso and sulphonyl hydrazones. There are also some blowing agent compositions whose blowing gas is released through an endothermic reaction between the two components.

1 Azo

Orange crystalline powder, relative molecular mass 116.1, relative density 1.65, fineness (200 mesh pass) ≥ 99.5%, moisture ≤ 0.1%, ash ≤ 0.1%. Soluble in alkali, insoluble in alcohol, gasoline, benzene, pyridine and other general organic solvents, insoluble in water. Decomposition temperature is 190～205°C, non-flammable. The gas output is 200～300ml/g, mainly nitrogen, carbon monoxide and a small amount

carbon dioxide. It is stable at room temperature and self-extinguishing, but it generates a large amount of gas due to decomposition when it is above 120°C, and it is prone to explosion in a closed container.

Uses: Suitable for PE, PVC, PS, PP, ABS and so on. Its decomposition products are non-toxic, odorless, and non-polluting. Pure white foams can be obtained. This product has a high decomposition temperature, resulting in uniform and dense bubbles. It is suitable for various foamed products such as closed-cell foams, normal pressure or pressurized foams, and thick or thin foams. Such as PVC and plastisol foams, polyolefins, calendered and molded foams, foamed artificial leathers, etc.

2-azobisisobutyronitrile

White crystal powder, relative density 1.1, volatile matter 1%, insoluble matter in methanol 0.1%, melting point >99°C. Soluble in methanol, ethanol, propanol, ether, petroleum ether and other organic solvents, insoluble in water. Decomposition temperature 98 ~ 110 °C, the release of nitrogen, gas output 130 ~ 155ml/g. It slowly decomposes at room temperature and deteriorates after being stored at 30°C for several months. Therefore, the product should be stored below 10°C.

Uses: Especially suitable for PVC, can also be used for epoxy resin, PS, phenolic resin and rubber. Low decomposition heat, about 125.6 ~ 167.5J/mol, so the amount of up to 40% does not cause the product to burn, can be made white products. This product has a low decomposition temperature and can be used for ordinary PVC pastes. The toxicity is great, which greatly limits its application. In recent years, its use as a foaming agent has been gradually reduced and it is mainly used as a polymerization initiator.

3 Diisopropyl azodicarboxylate

An orange oily liquid with a relative molecular mass of 202, a solidification point of 2.4°C and a boiling point of 75.5°C (33.31 Pa). When heated alone, it is stable at 240°C. The use of heat stabilizers such as lead salts, organotin compounds, cadmium soap, and zinc soaps can activate them and lower the decomposition temperature. The amount of gas generated at 100 to 200°C is 200 to 350 ml/g. Soluble in common plasticizers.

Uses: Liquid foaming agent, suitable for PE, PP, PVC and so on. Easy to disperse in plastic, cell structure is uniform and dense, decomposition products are odorless, non-toxic, colorless and non-polluting, and can produce foam with extremely light color. Adjust the formulation and processing conditions to produce closed or open-cell foams.

4 Azodicarboxylic acid

Bright yellow powder, relative molecular mass 253.37, relative density 1.67, decomposition temperature 240-250°C. The gas yield is 170 to 175 ml/g, and nitrogen, carbon monoxide, carbon dioxide, and barium carbonate are produced by decomposition. Insoluble in common solvents.

Uses: High temperature foaming agent. High decomposition temperature, good processing security. Suitable for high softening point polymers, especially PP. As a foaming agent for injection molding and extrusion molding of nylon resin, it also has a good effect. Can also be used for hard and semi-rigid PVC, ABS and so on.

5Diethyl azodicarboxylate

Red odorless oily liquid. The relative molecular mass is 174.16. Decomposition temperature 110 ~ 120 °C. Air volume 190ml/g. Soluble in plasticizers. Storage stable. No response to vulcanization accelerators. Sensitive to changes in moisture and pH. Metal salts (metals such as Cu, Fe, Co, Pb, Al, Sn) promote decomposition.

Uses: PVC and its copolymers, PE, polyester, epoxy resin, PS, rubber foaming agent. The dosage is 0.5 to 10%.

6 Azoaminobenzene

Yellow-brown crystal with special smell. The relative molecular mass is 197.24. Melting point 96 ~ 98 °C, decomposition temperature 150 °C. Air volume 113ml/g. Storage stable. It is easy to precipitate crystals from the surface of products, and it will decompose at lower temperatures in acidic media. It is a contaminating foaming agent.

Uses: It can be used as foaming agent for PVC and its copolymers, PS, PE, phenolic resin, epoxy resin, raw rubber and rubber, silicone polymer. The amount of 0.1 to 5%.

7 Nitroso compounds

The pale yellow crystalline powder is odorless and has a formaldehyde smell in the wet state. The relative molecular mass is 186.18. Relative density: 1.45. Solubility (room temperature, g/100 g solvent): methyl ethyl ketone 1.6, pyridine 1.8, ethyl acetoacetate 2.6, acetonitrile 5.6, morpholine 2.0, 1-nitropropane 1.4, dimethylformamide 14.7. Its solubility in water, ethanol, benzene, ether and acetone is about 1. Decomposition temperature is 190-205°C (in air), 130-190°C (in resin or using decomposition aid). The gas output was 260-270 ml/g. The decomposed gas is mainly nitrogen, with a small amount of carbon monoxide and carbon dioxide. This product is flammable. It will burn quickly when in contact with acid or acid mist. Therefore, it cannot be stored together with these substances and open flames should be strictly prohibited.

Uses: Used as a foaming agent for PVC. A large amount of gas, high foaming efficiency. The use of organic acids such as salicylic acid, adipic acid, or phthalic acid, or urea as the foaming aid can reduce the decomposition temperature (usually adjusted to 90-130°C). Decomposition of heat, can easily lead to thick products, "core burning", and decomposition products have foul odor. After using urea, odor can be eliminated. The amount of this product in PVC is about 7 ~ 15%.

8N,N'-dimethyl-N,N'-dinitrosoterephthalamide

The active ingredient in the commercial product is 70%. Yellow powder, relative molecular weight 250.21, relative density 1.2. The decomposition temperature in the air was 105°C, the resin was 90-105°C, the gas evolution amount was 126 ml/g, and the decomposition gas was mainly nitrogen. Pure products are explosives, sensitive to impact and friction, so the goods are filled with inert fillers to increase safety.

Uses: It can be used as PVC foaming agent, especially for PVC paste. It can produce open-cell and closed-cell foam without using foaming aid. Decomposition of heat is small, can be used for thick products, decomposition residue without pollution, but in the plastic will be blooming.

9 sulfonyl hydrazides - benzene sulfonyl hydra

Light yellow or white fine powder with a molecular weight of 172.20. The relative density of 1.43 ~ 1.48, the melting point of 99 °C. The decomposition temperature in the air is >95°C, and the decomposition temperature in plastics is 95 to 100°C. The amount of gas generated was 130 ml/g, and the decomposition gas was mainly nitrogen with a small amount of water vapor.

Uses: Can be used for PVC, phenolic resin, polyester foaming agent. Decomposition process accompanied by fever, so that the internal temperature of the product, it is best mixed with sodium bicarbonate. Sulfur compounds produced after decomposition of this product have an odor.

10 pairs of tosylhydrazones

White crystalline fine powder. Relative molecular mass 186. Relative density 1.40 to 1.42. Melting point 100 ~ 110 °C. Soluble in alkali, soluble in methanol, ethanol, methyl ethyl ketone, slightly soluble in water, aldehydes, insoluble in benzene and toluene. Decomposition temperature 100 ~ 110 °C, release nitrogen and a small amount of water, gas volume 110 ~ 125ml / g. Hydrolysis in hot water produces sulfonic acid and releases nitrogen. There is no hygroscopic deliquescence under normal temperature and the chemical properties are stable. This product is a flammable substance, but the acid does not catch fire.

Uses: This product is a low temperature foaming agent, suitable for PVC and other plastics and rubber. The gas and decomposition residues that occur are non-toxic, odorless, and non-polluting. The cell structure produced by this product is fine and uniform, the product shrinkage is small, and the tear strength is high. It is especially suitable for the manufacture of closed cell foam and sponge rubber. This product can be used to produce a white foam in PVC, but in this case the mold surface must be chrome plated. Due to the low decomposition temperature of the product, the temperature during the kneading process should be avoided (usually lower than 80 °C) to prevent premature foaming. This product can be used without foaming aids. This product can not be used in combination with the blowing agent H, because the two blowing agents react to produce a lot of heat, which can cause the product to burn inside. This product should not be combined with lead and lead, so as not to produce black lead sulfide precipitation.

114,4'-Oxide Benzene Sulfonyluene

White or light yellow crystalline powder. The relative molecular mass is 358.39. Relative density 1.52. The decomposition temperature was 140-160°C, nitrogen and water vapor were emitted, and the gas generation amount was about 120 ml/g. Soluble in cyclohexanone, ethylene glycol, ethyl ether, slightly soluble in ethanol and warm water, insoluble in benzene and gasoline.

Uses: This product is an extremely versatile foaming agent, known as a universal foaming agent. Can be used for PVC, PE, PP, ABS resin, etc., can also be used as a blend of plastic and rubber and a variety of synthetic rubber foaming agent. Although its structure contains ether bonds, it is very stable. The decomposition temperature in the resin is 120 to 140°C. The use of sodium bicarbonate can activate it, reducing the decomposition temperature. The cell structure is fine and uniform, and the decomposition gas and residue are non-toxic, odorless, and do not pollute the product. Applicable to the manufacture of PE foam wire and cable insulation materials, microporous PVC paste foam and other foam plastics. This product is highly safe for processing, and it has no premature foaming within 100°C. However, this product releases water when it is decomposed and foamed, so it is not suitable for water-repellent applications.

123,3'-disulfonyldiphenyl sulfone

Off-white powder. The relative molecular mass is 406.45. Relative density 1.60. The decomposition temperature in air is 148C, and the decomposition temperature in vinyl plastic is 135 to 145C. Hair volume 110ml/g. Non-toxic.

Uses: This product is mainly used as a soft PVC foaming agent, also can be used for rigid PVC and PE. The gas generated by the decomposition during foaming has no offensive odor and is non-toxic, but the residue is contaminated and can make the product colored.

13-1,3-diphenylsulfonyl hydrazide

Commodity in the form of a mixture of 50% of this product and 50% of chlorinated paraffin. It is a paste containing fine white particles with a relative molecular mass of 266.29 and a relative density of 1.5. The decomposition temperature in air is about 150°C, the decomposition temperature in plastics is 115 to 130°C, and the gas evolution volume is 300 ml/g.

Uses: This product can be used as a blowing agent for rubber and plastics, mainly used for rubber. The processing safety is high and the risk of premature foaming is small. Alkaline substances can lower their decomposition temperature. The gas produced by the decomposition is mainly nitrogen.

14 p-toluenesulfonamide semicarbamide

White fine powder. The relative molecular mass is 229.25. Soluble in dimethyl sulfoxide, dimethylformamide, dimethylacetamide, concentrated ammonium hydroxide and alkali water, insoluble in acetic acid, acetone, carbon tetrachloride, ethylene glycol, isopropyl alcohol, petroleum ether, Toluene and water. The decomposition temperature in air is 230°C, and the decomposition temperature in plastics is 213 to 225°C. The gases released are mainly nitrogen and carbon dioxide (about 2:1). The decomposed solid residue is mainly para-xylene disulfide and ammonium p-toluenesulfonate, the former being soluble in benzene and the latter soluble in water. This product has a good storage stability at room temperature, but should be close to the steam pipe, fire and direct sunlight.

Uses: This product is a high temperature nitrogen blowing agent, especially suitable for high temperature processing of plastics, such as ABS resin, nylon, rigid PVC, HDPE, PP, PC and so on. The processing safety is good and there is no danger of premature foaming. This product can also be used for natural rubber and synthetic rubber foam.

154,4'-Oxobis(phenylsulfonamide semicarbazide)

This product is a high-temperature foaming agent with a decomposition temperature of 210-220°C and a gas generation volume of approximately 145ml/g. The gases released are mainly nitrogen and carbon dioxide.

Uses: Suitable for rigid PVC, HDPE, high softening point PP, PC, ABS resin and other high processing temperature plastics.

16 trimethyltriazine

White or off-white powder. The relative molecular mass is 171.61. Decomposition temperature 235 ~ 275 °C. The amount of gas is about 247ml/g. The gases released are mainly nitrogen and carbon dioxide.

Uses: This product is a high temperature foaming agent, suitable for hard and semi-rigid PVC, PP, PC, ABS resin, polyamide and other processing temperature of plastic. Processing safety is good.

175-phenyltetrazole

Liquids. Relative density 1.105 (50°C).

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