What is Polyurethane Foam?

Polyurethane rigid foam is made of isocyanate and polyether as main raw materials. It is polymerized by high-pressure spraying and on-site foaming under the action of various auxiliary agents such as foaming agents, catalysts, and flame retardants. Thing. There are two types of polyurethane foam: soft foam and rigid foam. Soft bubbles have an open-cell structure and hard bubbles have a closed-cell structure; soft bubbles are classified into crusted and non-crusted.

Polyurethane foam

Foam plastic is one of the main varieties of polyurethane synthetic materials. Its main feature is porosity, so its relative density is small.

Higher specific strength. According to the different raw materials used and the formulation changes, it can be made into soft, semi-rigid and rigid polyurethane foams. If it is classified according to the type of polyol used, it can be divided into polyester type, polyether type and castor oil. Type polyurethane foam, etc .; if classified by foaming method, there are block, molded and sprayed polyurethane foam and other types.

Polyurethane foam is widely used in almost all sectors of the national economy, especially in furniture, bedding, transportation, refrigeration, construction, and thermal insulation. It has become one of the indispensable materials. It has become one of the most widely used varieties in plastics. Polyurethane soft foam is mainly used for furniture, bedding and other household items, such as sofas and seats, back cushions, mattresses and pillows; polyurethane rigid foam is mainly used for thermal insulation, refrigerating and freezing equipment and cold storage, thermal insulation panels, wall insulation , Pipe insulation, thermal insulation of storage tanks, single-component foam jointing materials, etc.

Uses of polyurethane foam

1. High efficiency and energy saving, no gap after filling, strong bonding after curing.

2. Anti-shock and compression, it will not crack, decay or fall off after curing.

3. It has ultra-low temperature thermal conductivity and heat-resistant insulation.

4. Efficient insulation, sound insulation, waterproof and moisture proof after curing.

5. The joint grout can adhere to concrete, coating, wall, wood and plastic surfaces ^[1] .

Application range of polyurethane foam

Business areas of this product: door and window engineering installation, home decoration, etc.

1. Seal and fix wooden, plastic steel, aluminum alloy and other metal door and window frames.

2. Wrap the sealed cable and wire box, air-conditioning tube, heat and cold water pipe.

3. Fill voids in masonry; fill voids in hulls.

4. Home maintenance: filling holes and gaps, repairing floor tiles and floors.

5. Landscaping and horticulture: flower arrangement, gardening and setting, light and beautiful.

6. Advertising exhibitions: manufacturing of models, sandboxes, and repair of display boards.

7. Packaging and transportation: Wrap valuable and fragile goods in an instant.

8. Refrigeration and air conditioning: caulking, sealing and heat insulation around cold storage and air conditioner.

Instructions for use of polyurethane foam

a) Remove dirt and grease from the construction surface, and moisten the part to be filled with a little water.

b) Use in the temperature range of 5 -40 . If it is used in the cold season, it is recommended to preheat the tank in an environment of 30 .

c) Shake vigorously for more than 1 minute before use.

d) Remove the cover, screw on the special construction gun, turn the tank upside down, slowly press the handle, and the construction can be carried out when the discharge is normal. The tank is in an inverted state during construction.

e) Remove the residue on the nozzle and valve with cleaning agent immediately after construction to avoid solidification and blockage.

f) Surface dry in 20-30 minutes, and elastic filling structure will be formed in 24 hours.

g) The molding filler can be cut, sanded, and sprayed. This product is not UV resistant, and further coating is recommended.

h) The validity period is 18 months. The production date is shown on the bottom of the tank.

Notes on polyurethane foam

a) Keep the tank out of the reach of children.

b) It is forbidden to pierce, burn and empty tanks, and keep away from fire and heat sources during construction.

c) During the transportation and storage process, open flames are strictly prohibited to avoid impact and sunlight. The temperature of the tank must not exceed 45 ° C.

d) Wear protective goggles and gloves and ensure good ventilation during construction.

e) If the foam comes in contact with the eyes or skin, rinse immediately with plenty of water and consult a doctor if necessary.

f) Do not invert. Under normal conditions, the tank is under pressure, and there is a danger of bursting if it is not handled properly.

g) This product contains isocyanate, and the uncured foam is irritating.

Examples of polyurethane foam accidents

The "11 · 15" fire disaster in Shanghai has claimed 53 lives. Although the accident was caused by illegal operations of unlicensed welders, it has been found that the real behind-the-scenes killers are these nylon mesh, moso bamboo sheets, and polyurethane foam.

Regarding polyurethane foam, whether it is an indispensable building decoration material internationally, the relevant departments must be clear. In fact, some domestic architectural decoration enterprises value its advantages. For example, compared with similar products, the decorative effect is better, strong adhesion, shock resistance, compression resistance, ultra-low temperature thermal conductivity, sound insulation, etc., so it is widely used in architectural decoration. use. Because of this advantage, compared with the fires of several dead people, naturally it will not give much impact to the entire building decoration market.

For the control of polyurethane foam, it still stays in densely populated public places. Many places have also issued relevant regulations, and Shenzhen has issued the "Announcement on Prohibiting the Use of Polyurethane Foam Materials for Decoration and Decoration in Public Gathering Places" and implemented inspections and rectifications in public places. As for the use of polyurethane foam on the facade of the building, it seems that it has not yet alerted the relevant departments. Judging from the "11 · 15" fire case in Shanghai, it is obvious that controlling the use of polyurethane foam cannot be restricted to public places such as densely populated entertainment places, shopping malls, and supermarkets. For densely populated corporate houses and high-rise residential houses, The area including interior decoration also needs to be controlled, and it is necessary to stipulate or take compulsory measures.

In response to the "11.15" major fire in Shanghai, relevant experts have called for the introduction of regulations as soon as possible. For example, scaffolds at construction sites must be constructed with flame-resistant and non-combustible materials. Polyurethane foam must be used for exterior wall insulation and interior decoration. Replace with non-combustible substances. This is related to the interests of the entire building and decorative materials industry. Moreover, under the current vigorous urbanization construction and strong market demand, it will inevitably move the whole body and there will be a fierce game. In this context, it seems quite difficult to stop polyurethane foam.

In fact, it is not only polyurethane foam, but also domestic architectural decoration materials, which are inevitable. Therefore, under the respect of human life and based on respect for life, the relevant departments do need to neglect building decoration materials or authoritatively release them, so that the public can know which are toxic or even highly toxic, and which are relatively safe when a fire occurs. Letting the public choose rationally is also a precautionary measure.

Fire prevention is a systematic project. Complete fire prevention facilities, people's fire awareness, and rapid emergency rescue mechanisms can minimize the occurrence of fires or reduce hazards, but control or stop using polyurethane such as life-saving to the maximum extent. Poisonous materials such as foam must also be included in the scope of fire protection system engineering. Similarly, how to prevent fires in a building and how to facilitate rescue in the event of a fire requires scientific considerations, that is, plugging loopholes from the source to reduce the occurrence of tragedies.

Recycling of polyurethane foam waste

Flexible foam recycling technology can be divided into two categories, one is the physical method, and the other is the chemical method. The physical method recycling technology is a method for recycling and reusing foamed plastics by adopting methods such as bonding and pressure molding, as fillers, and extrusion molding. This method is simple and easy to use, and is relatively mature, but the recovered foam is suitable for Low-grade products, and aging is eliminated faster. The chemical recovery technology process is relatively complicated, and the industrialization is relatively late. Until now, new degradation methods continue to appear, but the foam performance of the final recovered material is better.

The following describes two methods of recycling flexible polyurethane foam

Polyurethane foam physical recycling method

1) Bonding and pressing

In this method, the polyurethane flexible foam powder is crushed into 3-10 mm pieces by a powder machine, and placed in a container with a stirrer, and sprayed with a reactive, one-component moisture-curing polyphenyl polymethylene. Polyisocyanate-based adhesive. The amount of adhesive is about 5% -10% of the weight of the waste material. After mixing, the foam sprayed with glue is put into a mold and molded at an appropriate compression ratio and cured at room temperature. After 12 hours or 40 minutes at 150 ° C, the finished product is obtained. The obtained recycled foam can be used as low-grade components such as packaging, automobile linings, carpet linings, and supports.

Adhesive pressure forming recycling polyurethane foam is the simplest and most mature method among all recycling methods. It has simple process and low investment, and is suitable for SME applications. According to reports, in the United States alone, more than 200,000 tons of flexible foam waste are crushed and bonded into recycled foam each year. Europe also mostly produces rebonded foam products from the scraps in the production of slabstock flexible plastics and the cushioned foam of old cars, sofas, beds, and seats. ICI Polyurethanes produces carpet linings from used car cushions. In 1997, Toyota Motor Corporation of Japan used the foam of recycled car seat cushions to crush and bond them and used them as sound insulation materials.

The tensile strength, tear resistance, and elongation at break of the recycled product recovered by this bonding and press molding are greatly reduced, and the hardness is increased. In addition, the surface quality of the recycled product is poor, so it is only suitable for Areas where tensile properties and surface properties are not critical.

2) as filler

The soft polyurethane waste foam is sieved and cleaned to completely remove possible metal impurities, and then pulverized into particles with a particle size of about 3mm, and then pulverized the particles into 180-300 at low temperature or using a two-roll mill room temperature pulverizer. ? M powder, and then add the powder as a filler to the new flexible foam composition. In this way, not only the waste foam plastic is recycled, but also the cost of new products is reduced, which is economically and technically feasible, which is very suitable for the self-digestion of waste materials in the factory of soft foam production plants.

For polyols added with fillers, the first thing to consider is its fluidity and viscosity increase, which are mainly related to the proportion of recycled materials added and the characteristics and particle size of the finely milled particles. Then consider its impact on product performance.

Studies have shown that when the added amount of the recycled material does not exceed 10%, the physical properties of the prepared soft foams have little difference compared with conventional foams, and have little relationship with the particle size of the recycled materials. However, with the increase in the amount of recycled materials and the increase in particle size, the viscosity of the polyol will increase sharply, which may cause problems such as difficult mixing of the mixing head of the foaming machine, excessive mixing pressure, and sluggishness of the composition when injected into the mold. This method of recycling polyurethane waste foam must improve the foaming equipment.

3) Extrusion

Extrusion molding is the use of thermodynamics to change the molecular chain in a flexible polyurethane foam into a medium-length chain, transforming the foam material into a soft plastic material. This material is suitable for plastics with high strength and high hardness, but low requirements on tensile and elongation at break. The specific method is to pulverize the foam into powder, blend it into thermoplastic polyurethane, and make it in an extrusion molding machine. Granules, using injection molding methods to manufacture soles and other products, the German Bayer company has done research in this area. This method is very suitable for recycling waste products and is not suitable for large-scale recycling.

Polyurethane foam chemical recovery method

Polyurethane is obtained by polymerizing isocyanate-NCO-containing compounds such as TDI and MDI with active hydrogen-containing compounds such as ROH and RNH2. The polymer contains urethane bonds and urea bonds. Two important reactions are as follows

OCN-R-NCO + HO ~~ OH OOCNH-R-NHCOO ~~ (Carbamate group) 2 NCO + H2O ~~ NHCONH ~~ (urea group) + CO2

Chemical recovery is the use of alcoholysis, hydrolysis, alkaline hydrolysis, and pyrolysis to break the urethane groups and urea groups in flexible polyurethane foam under certain conditions, and decompose them into polyols, aromatic amines, carbon dioxide, etc., and then The decomposed product is separated by equipment such as distillation to achieve the purpose of recovery.

1) Alcoholysis

Among the researches on the chemical recovery of soft polyurethane waste, the alcoholysis method is the most active, and it has achieved good economic and environmental benefits. Many alcoholysis methods have been studied. Among them, small molecule alkyl diols are mainly used as alcoholysis agents. Alcohols and co-alcolytic agents such as alcohol amines, tertiary amines, and organometallic compounds are used in certain proportions. Under the effect of the reaction, the reaction temperature is controlled at 150-250 ° C for an alcoholysis reaction for 1 to 5 hours, and a mixture of a regenerated polyol and an aromatic amine can be obtained. There are two main types of reaction decomposition processes:

a. Transesterification of urethane groups

Ordinary polyurethane materials mainly contain urethane characteristic groups. Under certain conditions, alcohols are susceptible to transesterification, and the bonds are broken to form polyether alcohols. The reaction is as follows:

R1 ~~ NHCOOR2 + HO OH

R1--NHCOO ~~ OH + R2OH

b. Decomposition of urea bond groups

In the preparation of flexible polyurethane foams, the raw materials will contain water to a certain extent or water will be added as a foaming agent. Water and isocyanate react to produce urea bond groups in the foam. The urea bond groups can also be decomposed by alcohol, thus A hydroxyl-containing urethane and the corresponding amine are produced. The reaction is as follows:

~~ NHCONH ~~ + HO ~~ OH

~~ NHCOO ~~ OH + NH2 ~~ <br> <br>

From the above two decomposition processes, the choice of the type and ratio of the alcoholysis agent and co-alcolytic agent is very important. It not only determines the process conditions such as reaction temperature and time, but also determines the properties of the alcoholysis products. Dihydric alcohols with different molecular weights are used as alcoholysis agents; the molecular weights of the produced polyols are also different. Generally speaking, the molecular weights of the polyols produced by high-molecular alcoholysis agents are also relatively high, which can be selected according to the needs of recycled polyols The alcoholysis agents used are ethylene glycol, propylene glycol, butanediol, pentanediol, diethylene glycol, dipropylene glycol, and the like.

For the co-alcolytic agent, alcohol amine, tertiary amine, alkali metal or alkaline earth metal acetate, titanate, etc. can be selected. The effective compatibility of the co-alcohol and alcoholysis agent can reduce the reaction speed and temperature, shorten the reaction time, and increase the reaction time. Alcoholysis reaction ability, reducing the amount of alcoholysis agent, facilitating the separation of recovered materials and the purification of recovered polyether. In some process classifications, the alcoholysis method is further divided into a diol method, an alcohol amine method, an alcohol coating method (also known as an alcohol-alkali metal hydroxide method), and an alcohol phosphate method according to the combination of an alcoholysis agent and a co-alcoholysis agent. . These several process methods have the same principle and slightly different effects. See Table 1 for the characteristics of each process.

Classification of alcoholysis process conditions and process characteristics Process conditions Glycol method alcohol amine method alcohol coating method alcohol phosphorus method alcoholysis agent C2 ~ C6 glycol C2 ~ C6 glycol

(90% -100%) OH equivalent is 30 ~ 1000

Polymerize diol and amine compound and use a molecular weight of 400 ~ 3000

Polypropylene glycol ether & nbsp; co-alcolytic agent tertiary amine C4 ~ C8 dialkanolamine

(0 ~ 10%) & nbsp; Alkali metal hydroxide halophosphate decomposition foam expansion factor 0.3 ~ 1.00.3 1.030 500.3 ~ 1.0 Decomposition temperature / 150 ~ 200175 25060 160170 250 Decomposition time / h4 83 ~ 151 53 5

Recyclables: Polyamine, Polyol Polyol Polyamine, Polyol Polyol, Ammonium Phosphate Recycling Method and Industrial Blend Use Blend with 20% ~ 40% Industrial Polyether. Use directly. Use foam directly.

Several alcoholysis processes are relatively simple, the equipment investment is small, and it is easy to operate. In comparison, the alcoholysis method has great advantages, and the recovered products can be directly used. Many foreign companies have put into industrial recycling production. Such as the Japanese Soflan company, the Dutch Terneuzen company, the British ICI company and DuVergier company established a joint venture in London with a recycling capacity of 3000 ~ 5000t / a high quality polyol factory.

2) Hydrolysis

The hydrolysis method is to catalyze the alkali metal hydroxide at 250-340 , and pass water vapor with a pressure of 50-150Kpa into the waste soft foam. The waste soft foam can be decomposed into amine, polyol, and CO2. The degradation reaction is as follows:

Rl ~ NHCOOR2 + H2O

R1-NH2 + R2OH + CO2

The decomposed amine and CO2 are taken out with the water vapor, and the amine compounds can be recovered after condensation, while the alcohol compounds are collected from the lower part of the cracker. The hydrolysis temperature is a guarantee of the yield and quality of the recovered material, and it has been reported that the optimal temperature is 288 ° C.

Because this method uses high-pressure water vapor, it is sometimes called water vapor cracking. The advantage of this method is that there are many types of recovered materials directly. The recovered polyol can be used to prepare flexible foam in a proportion of 5%. In comparison, the density, tensile strength, and elongation all increased, but the tear strength decreased. The disadvantage is that the hydrolysis temperature is relatively high, the obtained amine cannot be directly used for the production of isocyanate, the polyol is difficult to be alcoholized to the required standard, and the cost is high, so this method has not yet achieved industrialization.

3) Alkali hydrolysis method

The alkaline hydrolysis method uses an alkali metal hydroxide such as one or more mixtures of NaOH, LiOH, KOH, and Ca (OH) 2 as a decomposition agent, and a quaternary ammonium salt or sulfate as an activator. In the decomposer of high-quality foam, the decomposition reaction is started by heating to 160 ° C under stirring, and the mixture is continuously stirred and kept for about 4 hours to obtain the alkali hydrolysis product polyol, divalent aromatic amine, sodium carbonate, and the like. The decomposition reaction formula is as follows: R1 ~~ NHCOOR2

R1 ~~ NCO + R2OH

R1 ~~ NHCONH ~~ R2

R1 ~~ NCO + R2OH

R1 ~~ NCO + 2NaOH

R1-NH2 + Na2CO3

The whole process consists of three parts: decomposition of foam, separation and recovery of toluene diamine, and purification and recovery of polyether polyol. The purity of the recovered toluenediamine can exceed 98.5%, and it can be directly used as a raw material for phosgenation reaction to produce isocyanate. The recovered polyol can also be directly used to prepare polyurethane foam, and its performance is close to that of conventional foam. Generally, 1000 kg of soft foam after cleaning can recover about 550 kg of polyalcohol and about 230 kg of toluenediamine, and the recovery rate is high. From the perspective of environmental protection and economics, the alkaline hydrolysis method is a good recovery method. However, the disadvantage is that the reaction is performed under the conditions of high temperature and strong alkali, which requires high equipment, large initial investment, and difficult industrialization.

4) Pyrolysis

There are two methods for pyrolysis of flexible polyurethane foam. One method is to crack in an inert gas atmosphere or an oxidizing atmosphere at a high temperature of 250-1200 ° C. The product is a gaseous and liquid mixture. When this method is used for cracking, the product is temperature-dependent. For example, the soft foam waste is cracked at 250-300 ° C. The product is basically equal amounts of isocyanate and polyol. The cracking is performed at 700-800 ° C. The product is pyrolysis gas and oil. And coke, the obtained pyrolysis gas is used as fuel for the pyrolysis reaction to save the cost of pyrolysis