| En
You are here: Media Center > Blog > PVC Foam Board

Complete list of foaming agents

Views:4 Publish Time: 2022-01-13 : Louis Lu

Complete list of foaming agents

1 Physical foaming agent


There are many kinds of physical foaming agents, such as aliphatic hydrocarbons, chlorinated hydrocarbons, hydrochlorofluorocarbons and carbon dioxide gases.  Since the 1950s, monochloromethane (CFC-11) has been widely used as the preferred foaming agent for polyurethane.  Due to its destructive effect on the atmospheric ozone layer, CFCs compounds must be prohibited in order to protect the global ecological environment. For many years, ideal alternative products have been sought and developed at home and abroad.  In addition to considering the properties of the foaming agent itself, the alternative foaming agent generally needs to properly adjust and improve the raw materials such as polyether polyol, defoamer and catalyst to optimize the formulation system.  Therefore, the key of physical foaming agent lies in the development and Application Research of alternative products. So far, there are mainly four alternatives to foaming agent CFC-11.


(1) Carbon dioxide foaming agent


There are two kinds of carbon dioxide foaming agents.  One is that isocyanate reacts with water to produce carbon dioxide (water foaming) as foaming agent, and the other is liquid carbon dioxide. Compared with CFC-11, the advantages of water foaming are that the ODP (ozone loss value) of carbon dioxide is zero, non-toxic, safe, there is no recycling problem, and there is no need to invest in the transformation of foaming equipment; The disadvantage is that the viscosity of polyol components is higher during foaming process, foaming pressure and foam temperature are higher, and the adhesion between foamed plastics and substrate is worse, especially the thermal conductivity of hard foam products is high. Because the diffusion rate of carbon dioxide from the bubble hole is faster, and the air enters the cavity slowly, thus affecting the dimensional stability of the foamed plastics, although it can be improved through modification, it is still not as good as CFC-11 foam material.


At present, it is mainly used in the fields of heat insulation, packing foam plastics and agricultural foam plastics, which are not very high insulation requirements. The advantages and disadvantages of liquid carbon dioxide foaming are the same as those of water foaming.  They are mainly used in flexible polyurethane foam, which can overcome the disadvantages of water foaming, increasing the consumption of isocyanates, the crispness of foam plastics and poor adhesion to substrates. However, the liquid foaming machine needs to be improved, and the storage and transportation cost of liquid carbon dioxide increases.  At present, the liquid carbon dioxide foaming technology is still under continuous research and development.


(2) Hydrochlorofluorocarbon foaming agent


Hydrochlorofluorocarbon (HCFC) foaming agent contains hydrogen in its molecule, which has unstable chemical properties and is easy to decompose.  Therefore, its ODP is far less than CFC-11.  Therefore, HCFC is regarded as the first generation alternative product of CFC foaming agent.  It should be used temporarily in the transition period and should be replaced by chlorine free compounds in a short time as possible.


At present, the European Union, the United States and Japan prohibit the use of HCFC foaming agents at the end of 2004, and the service life in China is 2030. At present, commercial CFC-11 can replace the most mature product of HCFC-14LB.  It has good compatibility with polyols and isocyanates.  Instead of adding equipment, HCFC-14LB can be directly replaced by CFC-11.  When the same density and similar physical properties of foam are achieved, the dosage should be less than CFC-11. The defect of HCFC-141B is that the raw material price is high, and it has solubility for some ABS and high impact polystyrene, and its thermal conductivity is higher than CFC-11.  Therefore, the foam density needed to be high is high enough to achieve the heat insulation effect.


Another kind of hydrochlorofluorocarbon product instead of CFC-11 is HCFC-22 / hcfc-14lb mixture of 60:40.  This kind of mixture is the most commonly used solvent in industrial production.  The production technology is mature and the price is moderate.  The disadvantage is that the solubility of HCFC-22 / HCFC-141b system in general polyols is relatively low, and it is relatively difficult to process polyols containing HCFC-22. In addition, the ODP value of HCFC-124 is only HCFC-141B 1/5, allowing longer service life.  Some foreign enterprises plan to use it in building and fridge foam, and compete with higher cost hydrofurane (HFC).


(3) Hydrocarbon foaming agent


The hydrocarbon compounds used in polyurethane foaming agents are mainly cyclopentane, especially the rigid foam system with cyclopentane, which has the advantages of low thermal conductivity and anti-aging properties.  The ODP value is zero.  It is often used in the fields of fridge, cold storage and building insulation, etc. , and has become the first choice of hard foam CFC-11 substitute in China.


In addition, using n-butane and isobutane as auxiliary foaming agents to prepare cyclopentane polyurethane rigid foam, the following two problems must be solved, and explosion-proof equipment shall be selected to solve the problems of flammability and explosion of cyclopentane; Certain measures, such as the use of pentane and isopentane with cyclopentane, can improve the fluidity of foam and solve the problem of poor solubility of cyclopentane in polyether polyols.


In recent years, great progress has been made in the production and development of cyclopentane in China.  High purity cyclopentane can be obtained by depolymerization and hydrogenation with C5 as raw material. The "cyclopentane product development" project undertaken by Beijing Research Institute of chemical industry has passed the appraisal.  At present, China's Jilin Longshan Chemical Plant, Beijing Dongfang Chemical Plant and Nanjing hongbaoli Co. , Ltd.  have successfully built cyclopentane production units, and cooperated with many famous refrigerator manufacturers in China to provide cyclopentane combined polyether for foaming materials.


(4) Hydrofluorocarbon (HFC) foaming agent


The HFC compound ODP is zero.  It is an ideal substitute for CFC-11 in the production of soft PU foam.  The early HFC foaming agents are mainly HFC-134A and HFC-152A.  These two foaming agents have low molecular weight and low boiling point.  When the foam with the same density and similar physical properties is used, the dosage is less than that of CFC-11, and the performance is relatively stable. However, their defects are high thermal conductivity and low solubility in general polyols.  It is relatively difficult to process the combined polyether containing HFC-134a and HFC-152a.  In addition, foaming equipment is required to meet the processing requirements.


Due to the shortcomings of these two products, people have accelerated the research and development of new HFC foaming agents. At present, research and development shows that HFC-245fa and fc-365mfc have great potential. These two products have similar characteristics to CFC-11.  The thermal conductivity is in the same range as HCFC-141b.  Their ODP value is zero, toxicity is very low, size stability is good, HFC-245fa has excellent electrical insulation performance, and the disadvantage is low boiling point; Hfc-365mfc has high boiling point, but it is flammable.


At present, the industry at home and abroad agree that the above two products are the most ideal substitutes for CFC-11, which have received special attention.  The pace of research and production is rapid, and foreign countries have entered the stage of industrial production.  For example, in October 2003, the Chemical subsidiary of Japan Central Glass Company built a HFC-245fa unit with an annual output of 5000t,At the end of 2002, Solvay company built a hfc-365mfc unit with an annual output of 15000 tons in France. It indicates that the high-performance foaming agent with high insulation performance and no damage to the ozone layer will be popularized and used all over the world.


(5) Other


In recent years, many foreign scientific research institutions have accelerated the research work on alternatives to CFCs foaming agent.  For example, Japan' s earth environment industry technology research institute has launched a specific new alternative compound hydrogenated polyether (HFE) and developed seven series of HFE products.  This product does not destroy the ozone layer and reacts with alcohols and fluorinated olefins with water as solvent.  The effect is very good.


In addition, with the development of CFCS alternative technology, the structure of surfactant products of polyurethane foam has changed greatly. During the foaming process of soft polyurethane, liquid carbon dioxide will be transformed into gas almost instantaneously, so surfactants are required to have strong nucleation ability, otherwise it is difficult to obtain the nucleation ability with excellent cell structure.  For example, the surfactant products of German Goldschmidt company and American Witco company are suitable for foaming soft polyurethane products with liquid carbon dioxide.


The research on CFCs substitution in China has made rapid progress.  At present, HCFC-141b and HCFC-22 are produced in large quantities.  Hydrofluorocarbon foaming agents HFC-134a and HFC-152a are developed based on foreign development experience.  High performance hf-245fa and hfc-365mfc are also studied and developed; The annual production capacity of cyclopentane has reached 10000 tons, and the production technology is at the international advanced level.


2 Chemical foaming agent


There are many kinds of substances used as chemical foaming agents.  According to the chemical structure, there are mainly n-nitrous compounds, such as N, n-dinitro pentamethyltetramine (DPT), N, N-dimethyl-N, n-bis-p-phenylenedicarbonamide (NTA), etc; Azo compounds, such as Azodicarbonamide (ADC), azodiisobutyronitrile, isopropyl azodicarboxylate, diethyl azodicarboxylate, diazo aminobenzene, barium azodicarboxylate, etc; Hydrazide compounds, such as 4,4-disulfonyl hydrazide diphenyl ether (obsh), p-phenylsulfonyl hydrazide, 3,3-disulfonyl hydrazide diphenylsulfone, 4,4-diphenyl disulfonyl hydrazide, 1,3-phenyldisulfonyl hydrazide, 1,4-phenyldisulfonyl hydrazide, etc. The main varieties used are blowing agents ADC, DPT, dbsh, etc.  ADC accounts for 90% of chemical blowing agents abroad and more than 95% in China.


(1) ADC foaming agent


China is the largest ADC producer and supplier in the world, with an annual production capacity of 150000 tons, accounting for about 50% of the global total production.  The average annual growth rate of production capacity from 1995 to 2003 was about 18%, showing a rapid development momentum. There are more than 30 manufacturers in 30 provinces and cities across the country, including Jiangsu Thorpe group, Zhejiang Juhua Group Company, Jiangxi electrochemical plant and Ningxia electrochemical plant, with an annual production capacity of 10000 tons; There are many improvements in production equipment, such as large-scale and continuous production equipment of sodium hypochlorite; Large scale condensation kettle and oxidation kettle; Use continuous drying process, etc. The control parameters of hydrazine hydrate synthesis process and oxidation process were optimized to improve the yield of each process and the comprehensive utilization of by-products. At present, the consumption structure of ADC foaming agent in China is; PVC accounts for about 40%, polyethylene 35%, polypropylene 12%, rubber 5% and others 8%. The annual export volume is 5000 ~ 6000 tons, and the products are mainly exported to Southeast Asia, Japan, South Korea, Russia and other places.


Although the production capacity and process technology of ADC in China have made great progress, hydrazine hydrate synthesized by urea method is still widely used as raw material, resulting in serious waste of resources and environmental pollution; In foreign countries, ADC foaming agent is mainly produced by ketone nitrogen method or hydrogen peroxide method. The most obvious difference is that only pure ADC products can be produced in China, and only a few manufacturers develop and produce limited varieties of modified ADC foaming agent, but the output is not high, the performance is unstable and the application range is narrow.


With the development of plastic industry, a single ADC foaming agent can not meet the demand, so modified ADC foaming agent came into being. Rich modification methods lead to the diversification, specialization and serialization of ADC varieties.  Modification research has become the key to the development of ADC.  Moreover, the ADC modification process basically has no three wastes, less investment and considerable economic and social benefits. In recent years, Shanghai Xiangyang Chemical plant has produced a series of ADC modified products ac-k.  when used in PVC artificial leather, the process is easy to control and the pores are fine; Juhua Group has also developed three modified products. However, there is still a big gap compared with foreign countries.  At present, hundreds of varieties have been developed abroad, there are still a large number of patent reports every year, and many new varieties continue to come out to dominate the market.  However, China mainly sells and exports ADC raw powder to provide primary raw materials for developed countries.  Therefore, pollution is left at home and profits are sent abroad, and the industry development lacks stamina.


The modification of ADC products is to optimize the gas evolution, particle size, color and thermal decomposition temperature of foaming agent.  The main ways are: changing certain reaction conditions or adding certain additives in the preparation process; ADC particle refinement; Add additives to ADC raw powder; Different types of foaming agents were compounded to achieve the modification effect.


At present, the main types of modified products are: (a) particle micronization. At present, ADC particles in China are coarse and few brands.  There are many brands according to different particle sizes abroad to meet the foaming needs of different synthetic materials. It is mainly to crush and grade the raw powder of foaming agent. (B) Low temperature type. The decomposition temperature of ordinary ADC is generally higher than 200 ℃.  Many resins with low softening point and easy aging under heating hope to have low-temperature decomposition products.


At present, the development of low temperature ADC is one of the main research topics in its modification field. One or more activators are mainly selected and combined with ADC in a certain proportion.  The activators can be metal compounds such as chromium, zinc and lead, urea derivatives and nitroguanidine.  After modification, the minimum decomposition temperature of ADC foaming agent can reach 80 ℃. (C) High dispersion type. In order to obtain a uniform polymer without holes and with smooth surface, it is required that the foaming agent can be completely dispersed in proportion in the polymer. Generally, ADC foaming agent is easily affected by static electricity and other factors, agglomerates and affects product quality. It is very important to develop high dispersion products.  ADC foaming agent can be mixed with the fine powder of some inert inorganic compounds.  In addition, surfactant can be added to ADC products to prepare high dispersion products. (D) Inhibit foaming type. Dicarboxylic acids and their hydrazides, phenols, amines and triazoles can inhibit the decomposition of ADC.  When there is a metal ionic activator, the inhibition effect is better. For example, adding foam inhibiting foaming agent material will cause uneven patterns due to the difference of foaming effect, so as to produce foamed wallpaper and other interior decoration materials. (E) Compound type. Other additives with specific functions can be mixed with ADC, or several foaming agents can be mixed with each other, and they can be combined into one according to the principle of synergy between various additives. Compound additives have become the mainstream of the development of plastic additives industry. (F) Foaming agent masterbatch. Like the development trend of other synthetic material additives, masterbatch has become one of the modification trends of foaming agent ADC. The masterbatch is obtained by mixing ADC, foaming additives and polymers, which effectively solves the problems of dispersion and dust pollution.  At present, it has not been developed in China. Americhem is the world' s most famous manufacturer of foaming agent masterbatch, supplying special ADC product series with the brand of supercell; Exocerol and other series of foaming agents launched by American Henly company are in the form of masterbatch.  For example, exocer01232 and lab010 are endothermic and exothermic blends, a038 is a mixture of several exothermic foaming agents, etc. Therefore, the key of ADC foaming agent in the future is to learn from foreign experience, vigorously develop endothermic, endothermic / exothermic and high-temperature decomposition foaming agents, and reduce dust pollution of foaming agent through masterbatch and surface modification.


(2) Foaming agent obsh


The chemical name of obsh foaming agent is 4,4 ' - di-sulfonylhydrazide diphenyl ether.  It is a common low-temperature foaming agent in plastic and rubber industry.  It is mainly obtained by the reaction of diphenyl ether sulfonated with hydrazine hydrate.  It was first developed and used in Japan, especially in the field of UHF wires and cables. Obsh foaming agent has the advantages of low decomposition temperature and no decomposition additives; Suitable for all kinds of synthetic materials; Extremely low toxicity, suitable for packaging materials in contact with food; Good electrical insulation; It has dual functions of vulcanizing agent and foaming agent; The pores are fine and uniform.


At present, a variety of modified series products of obsh foaming agent have been developed abroad, such as n#3000, 5000, 100s, 100m and other modified products of obsh foaming agent made by Yonghe chemical in Japan. China has also researched and developed obsh foaming agent.  At present, Shanxi Chemical Research Institute and Hangzhou Haihong company have built small-scale production units. The application of obsh foaming agent is limited due to its relatively high price.


(3) Foaming agent DPT


Chemical name: n, n ' - dinitro pentamethylene tetramine.  It is mainly used as rubber foaming agent with high decomposition heat.  Urea, urea derivatives and melamine are often added to prevent irritating odor.  It is basically not used for plastic foaming


Principle and characteristics of chemical foaming agent

Chemical blowing agents can also be divided into two main types: organic chemicals and inorganic chemicals. There are many kinds of organic chemical foaming agents, while the types of inorganic chemical foaming agents are limited. The earliest chemical foaming agents (about 1850) were simple inorganic carbonates and bicarbonates. These chemicals release CO2 when heated, and they are eventually replaced by a mixture of bicarbonate and citric acid, which has a much better prognosis. The chemical mechanism of today' s better inorganic foaming agents is basically the same as the above, which is the mixture of poly carbonic acids and carbonates.


The decomposition of polycarbonate is an endothermic reaction.  At about 320 ° F, about 100cc.  CO2 can be released per gram of acid.  When further heated to about 390 ° F, more gas will be released. The endothermic nature of this decomposition reaction may bring some benefits, because the dissipation of heat in the foaming process is a big problem. In addition to being used as a gas source for foaming, such substances often use the nucleating agent of crop hair foaming agent. It is believed that the initial cell formed during the decomposition of this kind of chemical foaming agent provides a migration place for the gas released by the subsequent physical foaming agent.


In contrast to inorganic foaming agents, there are many kinds of organic chemical foaming agents available, and their physical forms are also different. Over the past few years, hundreds of organic chemicals that may be used as foaming agents have been evaluated. There are many criteria to judge. The most important ones are: under the conditions of controllable speed and predictable temperature, the released gas is not only large, but also has good reproducibility; The gas and solid produced by the reaction are non-toxic, and shall not have any adverse effect on the foamed polymer, such as color or bad smell; Finally, there is the issue of cost, which is also a very important criterion. The foaming agents used in today' s industry are most in line with these guidelines.  


Low temperature foaming agent is selected from many optional chemical foaming agents.  The main problem that should be considered is that the decomposition temperature of foaming agent should adapt to the processing temperature of plastic. Two kinds of organic chemical foaming agents have been widely accepted by low temperature PVC, low density polyethylene and some epoxy. The first is toluene sulfonyl hydrazine (TSH). This is a milky yellow powder with a decomposition temperature of about 110 ° C. About 115cc of nitrogen and some water are produced per gram. The second is oxidized bis (benzenesulfonate) rib, or obsh. This foaming agent may be more commonly used in low-temperature applications.  This material is white fine powder and its normal decomposition temperature is 150 ° C. If an activator such as urea or triethanolamine is used, this temperature can be reduced to about 130 ° C. 125cc gas can be released per gram, mainly nitrogen. The solid product after obsh decomposition is a polymer.  If it is used together with TSH, it can reduce the odor.  


High temperature foaming agent for high temperature plastics, such as heat-resistant ABS, UPVC, polypropylene with low melt index and engineering plastics, such as polycarbonate and nylon, it is more appropriate to use foaming agent with higher decomposition temperature. Toluene sulfonphthalein aminohore (TSS or TSSC) is a very fine white powder with a decomposition temperature of about 220 ° C and a gas output of 140CC per gram.  It is mainly a mixture of nitrogen and CO2, with a small amount of CO and ammonia. This foaming agent is commonly used in polypropylene and some ABS. However, due to its decomposition temperature, its application in polycarbonate is limited. Another high temperature foaming agent, 5-benyltetrazole (5-pt), has been successfully used in polycarbonate. It begins to decompose slowly at about 215 ° C, but the gas production is small.  A large amount of gas will not be released until the temperature reaches 240-250 ° C, and this temperature range is very suitable for the processing of polycarbonate. The gas production is about 175cc / g, mainly nitrogen. In addition, there are some tetrazole derivatives under development, which have higher decomposition temperature and emit more gas than 5-pt.  


Azodicarbonate is the processing temperature of most major industrial thermoplastics, and its range is as described above. Most polyolefin, polyvinyl chloride and styrene thermoplastics have processing temperatures in the range of 150-210 ° C. For this kind of plastics, one kind of foaming agent is azodicarbonate, also known as Azodicarbonamide, or ADC or AC for short. In the pure state, it is a yellow / orange powder, which begins to decompose at about 200 ° C.  the gas production during decomposition is 220cc / g.  the gas produced is mainly nitrogen and Co, with a small amount of CO2 and ammonia under some conditions. The solid decomposition product is beige, which can not only be used as an indicator of complete decomposition, but also has no adverse effect on the color of foamed plastics.  


AC has been widely used as foaming agent for foamed plastics.  For many reasons, AC is one of the most effective foaming agents, and the gas released from it is highly efficient. And the gas release speed is fast and not out of control. AC and its solid products are substances with low toxicity. AC is also one of the lowest price chemical foaming agents.  It is quite cheap not only in terms of gas production efficiency per gram, but also in terms of gas production per dollar.  


In addition to the above reasons, AC can be widely used because of its decomposition characteristics. It can change the temperature and speed of the released gas, and can be used for almost all purposes in the range of 150-200 ° C. Activation, or action additive, changes the decomposition characteristics of chemical foaming agent, which has been mentioned in the use of obsh. The activation of AC is much better than that of any other chemical foaming agent. There are a variety of additives, first of all metal salts, which can reduce the decomposition temperature of AC.  the degree of decline mainly depends on the type and dosage of additives selected. In addition, such additives also have other functions, such as changing the gas release rate; Or a delay period or induction period occurs before the decomposition reaction begins. Therefore, almost all gas release modes in the process can be designed artificially.


The size of AC particles will also affect the decomposition process.  Generally speaking, at a given temperature, the larger the average particle size, the slower the release of gas. This phenomenon is particularly evident in systems with activators. Therefore, the particle size range of commercial AC is 2-20 microns or more, and the user can choose at will. Many processors have developed their own activation systems, and some manufacturers choose various pre activation mixtures provided by AC manufacturers. There are many stabilizers, especially for PVC, and some pigments will act as activators for ac. Therefore, care must be taken when changing the formula, because the decomposition characteristics of AC may also change.  


There are many grades of AC available in industry, which can be selected not only in particle size and activation system, but also in fluidity. For example, an additive added to AC can increase the fluidity and dispersibility of AC powder. This kind of AC is very suitable for PVC plasticized paste. Because foaming agents can be fully dispersed into plasticizers, this is the key to the quality of final products of foamed plastics. In addition to the grade with good fluidity, AC can also be dispersed in phthalate or other carrier systems. It will be handled as easily as a liquid.