Flame retardant polyurethane foam and preparation method thereof

Abstract

The present invention discloses a polyurethane foam containing a novel MOF flame retardant material. It comprises a component A combined polyether and a component B isocyanate. Among them, the component A combined polyether contains a MOF flame retardant material. The MOF flame retardant material is a phosphoric acid-modified metal organic framework composite material. The phosphorus-containing MOF in the system can significantly improve the flame retardant effect of the polyurethane foam and extend the flame retardant time of the foam. At the same time, since the surface of the MOF material has a large number of carboxyl groups and hydroxyl groups, it can be connected to the polyurethane foam matrix through chemical bonds, which can significantly reduce the migration of the flame retardant component, so that the flame retardant can play its most effective flame retardant role in the material. At the same time, since MOF has good chemical stability and thermal stability, the thermal stability of the polyurethane foam can be improved in the polyurethane foam. The composite MOF flame retardant provided by the present invention is green and environmentally friendly, will not pollute the environment, and has good industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethane, and in particular to a method for increasing the flame retardancy of polyurethane foam using phosphorus-containing MOFs. Background Art

[0002] Rigid polyurethane foam is a polymer material made from isocyanate and polyol as the main raw materials. It has excellent thermal insulation and mechanical properties and is widely used in chemical and petroleum pipelines, cold storage, cold chain transportation, and building insulation for anti-corrosion and heat preservation. However, polyurethane foam without flame retardant treatment is easy to burn and will release a lot of smoke and toxic and harmful gases, which poses many potential hazards.

[0003] In the prior art, Chinese patent CN 201210585597 discloses a phosphorus magnesium aluminum high-efficiency smoke suppression flame retardant for polyurethane foam, which mainly adds magnesium hydroxide, aluminum hydroxide, and sodium tetraborate to improve the flame retardant and smoke suppression properties of polyurethane foam. Chinese patent CN201010267725.9 discloses a low-smoke flame retardant polyurethane foam with all-inorganic flame retardant, which has good flame retardant and smoke suppression effects. However, the flame retardant durability of common inorganic additive flame retardants is poor, and they are easy to migrate and cause secondary pollution to the environment. Environmental protection laws and regulations have strictly limited the use of traditional halogen flame retardants.

[0004] Metal organic frameworks (MOFs) are an organic-inorganic complex whose metal centers are mostly transition metals, such as Zr and Fe, which can catalyze the dehydrogenation reaction of polymers, improve the efficiency of cross-linking carbonization, and stabilize the residual carbon structure at high temperatures. At the same time, phosphorus and halogens are introduced into the MOF structure, and the flame retardant effect in the system is enhanced through the catalytic effect of the central transition metal and the synergistic effect of the phosphorus-containing flame retardant; at the same time, since there are a large number of hydroxyl / carboxyl groups in the MOFs structure, they can be combined with the groups through chemical bonds, thereby reducing the migration problem of the flame retardant, and it is expected to develop a new type of flame-retardant rigid polyurethane foam. Summary of the invention

[0005] In view of this, the present invention provides a method for increasing the flame retardancy of polyurethane foam by adding phosphorus-containing MOFs. The present invention provides flame-retardant rigid polyurethane foam, which uses phosphorus-containing MOFs as flame retardants to improve the flame retardancy of polyurethane foam. At the same time, due to the chemical reaction between the surface carboxyl and hydroxyl groups and the matrix, the migration problem can be reduced, thereby reducing secondary pollution to the environment. At the same time, since MOF has good chemical stability and thermal stability, the polyurethane foam added with the MOF has good thermal stability.

[0006] The present invention adopts the following technical solutions:

[0007] A flame retardant polyurethane foam, wherein the foam material is prepared from component A and component B, wherein the mass ratio of component A to component B is 1:1 to 1:1.4, preferably 1:1 to 1:1.2;

[0008] The component A comprises the following components: by mass:

[0009] Polyether polyol 1, added in an amount of 5-20 parts, preferably 10-15 parts;

[0010] Polyether polyol 2, added in a ratio of 40-80 parts, preferably 50-70 parts;

[0011] Catalyst, added in an amount of 1-4.5 parts;

[0012] Foam stabilizer, added in an amount of 1.5-3 parts;

[0013] Cross-linking agent, added in an amount of 1-10 parts;

[0014] Water, added in an amount of 0.2-2 parts;

[0015] Physical foaming agent, added in an amount of 10-15 parts;

[0016] Flame retardant MOF, added in an amount of 1-20 parts, preferably 10-16 parts;

[0017] The component B is a polyisocyanate.

[0018] In the present invention, the polyether polyol 1, the initiator is sorbitol and / or a sucrose-glycerol composite initiator, the polymerization unit is propylene oxide, the hydroxyl value of the polyether polyol 1 is 300-600 mgKOH / g, preferably one or more of Wanhua Chemical SYPG086, A490, R8336, Tianjin Sanshihua 450L;

[0019] In the present invention, the polyether polyol 2 is a polyether polyol whose initiator is propylene glycol and whose polymerization units are propylene oxide and / or a polyether polyol whose initiator is glycerol and whose polymerization units are propylene oxide and ethylene oxide. The hydroxyl value of the polyether polyol 2 is 20 to 150 mgKOH / g, and is preferably one or more of Wanhua Chemical F3135, F3156, and A210.

[0020] In the present invention, the catalyst is one or more of amine, organic metal, and metal salt catalysts, preferably one or more of PC-8, PC-5, LCM-1, T12, and LCM-1.

[0021] In the present invention, the foam stabilizer is a polyether-modified polysiloxane, preferably one of L-6863, Y-16368 of Maitu and M8805 of Meside.

[0022] In the present invention, the crosslinking agent is one or more of ethylene glycol, diethylene glycol, glycerol, 3-3'-dichloro-4-4'-diphenylmethanediamine (MOCA), 3-5-diethyltoluenediamine (DETDA), and triethanolamine.

[0023] In the present invention, the physical foaming agent is one or more of HFC-245fa and HFC-141b.

[0024] In the present invention, the polyisocyanate is one or more of HDI, HMDI, TDI, MDI, PM200, PM400, and PM700.

[0025] In the present invention, the flame retardant MOF is prepared by a hydrothermal method from raw materials including metal salts, organic ligand molecules, solvents and organic acids.

[0026] In the present invention, the metal salt is one or more of zirconium oxychloride, zirconium chloride, cupric chloride and ferric chloride.

[0027] In the present invention, the organic ligand molecule is 2-amino-p-dibenzoic acid.

[0028] In the present invention, the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide and methanol.

[0029] In the present invention, the organic acid is one or more of acetic acid, formic acid and benzoic acid.

[0030] In the present invention, the method for preparing the flame retardant MOF comprises the following steps:

[0031] 1) Add a certain proportion of metal salt, organic ligand molecule, solvent and organic acid into a hydrothermal reactor;

[0032] 2) Place the hydrothermal kettle in an oven at a certain temperature and react for several hours;

[0033] 3) After the reaction is completed, the hydrothermal autoclave is cooled to room temperature;

[0034] 4) centrifuging the product and washing it several times with a solvent;

[0035] 5) drying the product;

[0036] 6) Weigh a certain proportion of the MOF and organophosphoric acid synthesized above and disperse them in DMF;

[0037] 7) placing the mixture under heating reflux at a certain temperature for several hours;

[0038] 8) Cool to room temperature, centrifuge the product, and wash and dry it.

[0039] The metal salt described in step 1) is one or more of zirconium oxychloride, zirconium chloride, cupric chloride and ferric chloride.

[0040] The organic ligand described in step 1) is 2-amino-p-dibenzoic acid.

[0041] The solvent in step 1) is one or more of N,N-dimethylformamide, dimethyl sulfoxide, and N,N-dimethylacetamide.

[0042] The organic acid in step 1) is one or more of acetic acid, formic acid and benzoic acid.

[0043] The reaction temperature in step 2) is 120-160°C; the reaction time is 24-48h.

[0044] In step 4), the solvent is methanol and / or DMF, and the number of washings is 1-5 times;

[0045] In step 5), the drying temperature is 150-180° C. and the drying time is 4-8 hours.

[0046] The organic phosphoric acid in step 6) is one or more of pyridoxal-5-phosphate, glyceraldehyde-3-phosphate, and phytic acid; the mass ratio of MOF to organic phosphoric acid is 1:1 to 1:2.5.

[0047] In step 7), the temperature of heating to reflux is 70-80° C. and the time is 11-12 h;

[0048] Finally, the present invention also provides a method for preparing a flame retardant polyurethane foam, comprising the following steps:

[0049] 1) Mix component A and keep the temperature at 21-22°C;

[0050] 2) Material A is mixed with material B which is also kept at a constant temperature of 21-22° C., and poured into a mold to obtain a polyurethane foam product.

[0051] The positive effects of the present invention are:

[0052] (1) The present invention uses phosphorus-containing MOF as a flame retardant to obtain an organic-inorganic composite flame-retardant polyurethane foam; the phosphorus-containing MOF in the system can significantly improve the flame retardant effect of the polyurethane foam and prolong the flame retardant time of the foam.

[0053] (2) At the same time, since the surface of the MOF material has a large number of carboxyl groups, it can be connected to the polyurethane foam matrix through chemical bonds, which can significantly reduce the migration of the flame retardant component, thereby reducing the secondary pollution caused by the flame retardant component to the environment.

[0054] (3) The MOF used in the present invention uses transition metals as nodes. The transition metals can catalyze the polyurethane foam to form carbon during the combustion process, thereby slowing down the combustion of the polyurethane foam and achieving a flame retardant effect. The metal ion centers in MOFs can form metal oxides during the combustion process and promote the polyurethane foam to form a dense, highly graphitized carbon layer; the NH4 + N2 can be formed during the combustion process, thereby diluting the oxygen in the environment and slowing down the combustion of polyurethane foam.

[0055] (4) MOF, as an organic-inorganic composite material, has good chemical stability and thermal stability. Its addition to polyurethane foam can improve the thermal stability of polyurethane foam. DETAILED DESCRIPTION

[0056] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0057] Raw material information:

[0058] Polyether polyol: polyether polyol SYPG086, produced by Wanhua Chemical (Ningbo) Rongwei Polyurethane Co., Ltd., functionality 6, hydroxyl value 480 mg KOH / g, molecular weight 700, industrial grade;

[0059] Polyether polyol A490, produced by Wanhua Chemical (Ningbo) Rongwei Polyurethane Co., Ltd., functionality 4.3, hydroxyl value 490 mg KOH / g, molecular weight 490, industrial grade;

[0060] Polyether polyol F3135, produced by Wanhua Chemical (Ningbo) Rongwei Polyurethane Co., Ltd., functionality 3, hydroxyl value 35 mgKOH / g, molecular weight 4800, industrial grade;

[0061] Polyether polyol A210, produced by Wanhua Chemical (Ningbo) Rongwei Polyurethane Co., Ltd., functionality 2, hydroxyl value 112 mgKOH / g, molecular weight 1000, industrial grade.

[0062] Cross-linking agent: Glycerol from Shenyang Shisan Biochemical Technology; triethanolamine from Aladdin, purity 98%.

[0063] Foam stabilizer: L-6863, Y-16368 from Momentive, M8805 from Meside.

[0064] Catalyst: PC-8, LCM-1, Evonik Chemicals.

[0065] Blowing agent: water; HFC-245ma, Honeywell; HCFC-141b, Henri Polymer Materials.

[0066] Polyisocyanate: polymerized DMI, brand: PM200 (viscosity 150-250 mPa·s), Wanhua Chemical.

[0067] Zirconium chloride: analytical grade, Aladdin Chemical Reagent Company.

[0068] Ferric chloride hexahydrate: analytical grade, Aladdin Chemical Reagent Company.

[0069] N,N-Dimethylformamide (DMF): analytical grade, MacLean Reagent Company.

[0070] 2-Amino-terephthalic acid: analytical grade, Aladdin Chemical Reagent Company.

[0071] Terephthalic acid: analytical grade, Aladdin Chemical Company.

[0072] Acetic acid: analytical grade, Aladdin Chemical Company.

[0073] Benzoic acid: analytical grade, Aladdin Chemical Company.

[0074] Pyridoxal 5-phosphate: analytical grade, Aladdin Chemical Reagent Company.

[0075] Phytic acid: 50%wt, Aladdin Chemical Reagent Company.

[0076] Methanol: analytical grade, MacLean Reagent Company.

[0077] Preparation of phosphorus-containing flame-retardant MOF:

[0078] A:

[0079] 1.05g zirconium chloride and 1.56g 2-amino-terephthalic acid were weighed and added to 40mL DMF, and 17mL acetic acid was added to the solution as a regulator, and ultrasonic treatment was performed for 15 minutes to fully dissolve the components in the DMF solvent. Then, the mixture was transferred to a Teflon-lined stainless steel reactor, and the reactor was placed in a 120°C oven for 48h. After the reaction was completed, it was cooled to room temperature, centrifuged, and repeatedly washed with DMF and methanol. The sample was dispersed in methanol for several days (methanol was replaced every 12h), centrifuged, and placed in a 170°C vacuum oven for activation for 8h to obtain NH2-Zr-MOF.

[0080] Weigh 5 g of NH2-Zr-MOF and 2 g of 5-pyridoxal phosphate and dissolve them in 40 mL of methanol solvent. Heat and stir at 80 °C in a three-necked flask for 12 h. After the reaction is completed, cool to room temperature, centrifuge and wash with methanol several times. Place the sample in a vacuum oven at 60 °C and dry for 12 h to obtain phosphoric acid-modified MOF (P-Zr-MOF) (MOF-1).

[0081] B:

[0082] 1.05 g zirconium chloride and 1.56 g 2-amino-terephthalic acid were weighed and added to 40 mL DMF, and 17 mL acetic acid was added to the solution as a regulator, and ultrasonic treatment was performed for 15 minutes to fully dissolve the components in the DMF solvent. Then, the mixture was transferred to a Teflon-lined stainless steel reactor, and the reactor was placed in a 135°C oven for reaction for 36 hours. After the reaction was completed, it was cooled to room temperature, centrifuged, and repeatedly washed with DMF and acetone. The sample was placed in a vacuum oven at 80°C and dried for several hours to obtain NH2-Zr-MOF.

[0083] Weigh 5 g of NH2-Zr-MOF and 5 g of 5-pyridoxal phosphate and dissolve them in 40 mL of methanol solvent. Heat and stir at 70 °C in a three-necked flask for 11 h. After the reaction is completed, cool to room temperature, centrifuge and wash with methanol several times. Place the sample in a vacuum oven at 60 °C and dry for 12 h to obtain phosphoric acid-modified MOF (P-Zr-MOF) (MOF-2).

[0084] C:

[0085] Weigh 0.7563g (2.77mmol) FeCl3.6H2O and 0.2534g (1.385mmol) 2-amino-terephthalic acid and dissolve in 60mL DMF. After stirring at room temperature for 30 minutes, the resulting solution is transferred to a Teflon autoclave. The reactor is placed in a 150°C oven for reaction for 24 hours. After cooling naturally to room temperature, it is washed three times with DMF and methanol. Centrifuge and wash repeatedly with DMF and methanol, disperse the sample in methanol for several days (replace methanol once every 12h), centrifuge and place it in a 170°C vacuum oven for activation for 8h to obtain NH2-MIL-88B-Fe.

[0086] Weigh 5 g of NH2-MIL-88B-Fe and 4 g of phytic acid (50% wt) and dissolve them in 40 mL of methanol solvent. Heat and stir at 75 °C in a three-necked flask for 11.5 h. After the reaction is completed, cool to room temperature, centrifuge and wash several times with methanol. Place the sample in a vacuum oven at 60 °C and dry for 12 h to obtain phosphoric acid-modified MOF (P-Fe-MOF) (MOF-3).

[0087] D:

[0088] Weigh 0.7563g (2.77mmol) FeCl3.6H2O and 0.2534g (1.385mmol) 2-amino-terephthalic acid and dissolve in 60mL DMF. After stirring at room temperature for 30 minutes, the resulting solution is transferred to a Teflon autoclave. The reactor is placed in a 140°C oven for reaction for 36 hours. After natural cooling to room temperature, it is washed three times with DMF and methanol. Centrifuge and wash repeatedly with DMF and methanol, disperse the sample in methanol for several days (replace methanol once every 12h), centrifuge and place it in a 170°C vacuum oven for activation for 8h to obtain NH2-MIL-88B-Fe.

[0089] Weigh 6 g NH2-Zr-MOF and 10 g phytic acid (50% wt) and dissolve them in 40 mL methanol solvent. Heat and stir at 80 °C in a three-necked flask for 11 h. After the reaction is completed, cool to room temperature, centrifuge and wash with methanol several times. Dry the sample in a vacuum oven at 60 °C for 12 h to obtain phosphoric acid-modified MOF (P-Fe-MOF).

[0090] (MOF-4).

[0091] E:

[0092] 1.05g zirconium chloride and 1.56g terephthalic acid were weighed and added to 40mL DMF, and 17mL acetic acid was added to the solution as a regulator, and ultrasonic treatment was performed for 15 minutes to fully dissolve the components in the DMF solvent. Then, the mixture was transferred to a Teflon-lined stainless steel reactor, and the reactor was placed in a 135°C oven for reaction for 36 hours. After the reaction was completed, it was cooled to room temperature, centrifuged and repeatedly washed with DMF and methanol. The sample was dispersed in methanol for several days (methanol was replaced every 12 hours), centrifuged and placed in a 170°C vacuum oven for activation for 8 hours to obtain Zr-MOF (MOF-5).

[0093] F:

[0094] Weigh 0.7563g (2.77mmol) FeCl3.6H2O and 0.2299g (1.385mmol) terephthalic acid and dissolve in 60mL DMF, and add 0.1g benzoic acid as a regulator. After stirring at room temperature for 30 minutes, the resulting solution is transferred to a Teflon autoclave. The reactor is placed in a 160°C oven for reaction for 24 hours. After natural cooling to room temperature, wash with DMF and methanol three times each. Centrifuge and wash repeatedly with DMF and methanol, disperse the sample in methanol for several days (replace methanol once every 12h), centrifuge and place it in a 170°C vacuum oven for activation for 8h to obtain Fe-MOF (MOF-6).

[0095] According to the composition raw materials and dosage in Table 3, the materials in each example were prepared respectively, and foamed manually to prepare the foam materials in Examples 1-8 respectively;

[0096] Manual foaming method: First, polyether polyol, catalyst, foam stabilizer, cross-linking agent, physical foaming agent, water and flame retardant MOF were fully mixed on a shaker. The mixed white material was placed in a 21°C oven for temperature control. The white material and the black material were mixed and stirred for 5 seconds, poured into a mold for foaming, and the foam sample was obtained after aging for 4 hours.

[0097] Flame retardant polyurethane foam material formulations in Examples 1-8 (unit, g)

[0098] Table 1 Formulation of polyurethane foam containing novel flame retardant MOF (unit, g)

[0099]

[0100] Table 2 Formulation of polyurethane foam in Comparative Examples 1-9 (unit, g)

[0101]

[0102]

[0103] Table 3 Foam properties of polyurethane foams prepared in Examples 1-8 and Comparative Examples 1-9

[0104]

[0105] It can be seen from the test results in Table 3 that compared with Comparative Example 1, the limiting oxygen index and thermal decomposition temperature of the polyurethane foams prepared in Examples 1-8 are increased; at the same time, compared with only adding Zr-MOF in Comparative Example 2, only adding Fe-MOF in Comparative Example 3, only adding phosphoric acid molecules in Comparative Example 4, and adding a physical mixture of MOF and phosphoric acid molecules in Comparative Examples 5 and 6, the limiting oxygen index and thermal decomposition temperature of the polyurethane foam prepared in Example 1 are increased.

[0106] The above shows that compared with polyurethane foam without phosphorus-containing MOF, polyurethane foam with only MOF or polyurethane foam with only phosphoric acid molecules, polyurethane foam with phosphorus-containing MOF has better flame retardant properties and thermal stability.

[0107] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A flame retardant polyurethane foam, wherein the foam material is prepared from component A and component B, wherein the mass ratio of component A to component B is 1:1 to 1:1.4; The component A comprises the following components: by mass: Polyether polyol 1, added in an amount of 5-20 parts; Polyether polyol 2, added in an amount of 40-80 parts; Catalyst, added in an amount of 1-4.5 parts; Foam stabilizer, added in an amount of 1.5-3 parts; Cross-linking agent, added in an amount of 1-10 parts; Water, added in an amount of 0.2-2 parts; Physical foaming agent, added in an amount of 10-15 parts; Flame retardant MOF, added in an amount of 1-20 parts; The component B is polyisocyanate; the preparation method of the flame-retardant MOF comprises the following steps: 1) Add a certain proportion of metal salt, organic ligand molecule, solvent and organic acid into a hydrothermal reactor; 2) Place the hydrothermal kettle in an oven at a certain temperature and react for several hours; 3) After the reaction is completed, the hydrothermal autoclave is cooled to room temperature; 4) centrifuging the product and washing it several times with a solvent; 5) drying the product; 6) Weigh a certain proportion of the MOF and organophosphoric acid synthesized above and disperse them in DMF; 7) placing the mixture under heating reflux at a certain temperature for several hours; 8) cooling to room temperature, centrifuging the product, and washing and drying it; the metal salt is one or more of zirconium oxychloride, zirconium chloride, cupric chloride, and ferric chloride; and / or the organic ligand molecule is 2-amino-p-dibenzoic acid.

2. The flame retardant polyurethane foam according to claim 1, characterized in that The solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, and methanol; and / or the organic acid is one or more of acetic acid, formic acid, and benzoic acid.

3. The flame retardant polyurethane foam according to claim 1, characterized in that The reaction temperature in step 2) is 120-160°C; the reaction time is 24-48h; and / or, the solvent in step 4) is methanol and / or DMF, and the number of washings is 1-5 times; and / or, the drying temperature in step 5) is 150-180°C; the drying time is 1-8h; and / or, the organic phosphoric acid in step 6) is one or more of pyridoxal-5-phosphate, glyceraldehyde-3-phosphate, and phytic acid; the mass ratio of MOF to organic phosphoric acid is 1:1-1:2.5; and / or, the heating reflux temperature in step 7) is 70-80°C, and the time is 11-12h.

4. The flame retardant polyurethane foam according to any one of claims 1 to 3, characterized in that: The polyether polyol 1, whose initiator is sorbitol and / or sucrose-glycerol composite initiator, whose polymerization unit is propylene oxide, has a hydroxyl value of 300-600 mgKOH / g; and / or, the polyether polyol 2, whose initiator is propylene glycol and whose polymerization unit is propylene oxide and / or whose initiator is glycerol and whose polymerization unit is propylene oxide and ethylene oxide, has a hydroxyl value of 20-150 mgKOH / g.

5. The flame retardant polyurethane foam according to claim 4, characterized in that The polyether polyol 1 is one or more of Wanhua Chemical SYPG086, A490, R8336, and Tianjin Sanshihua 450L; and / or, the polyether polyol 2 is one or more of Wanhua Chemical F3135, F3156, and A210.

6. The flame retardant polyurethane foam according to any one of claims 1 to 3, characterized in that: The catalyst is one or more of amine, organic metal, and metal salt catalyst; and / or the foam stabilizer is polyether-modified polysiloxane.

7. The flame retardant polyurethane foam according to claim 6, characterized in that The catalyst is one or more of PC-8, PC-5, LCM-1, T12; and / or the foam stabilizer is one of L-6863, Y-16368 of Maitu, and M8805 of Meside.

8. The flame retardant polyurethane foam according to any one of claims 1 to 3, characterized in that: The cross-linking agent is one or more of ethylene glycol, diethylene glycol, glycerol, 3-3'-dichloro-4-4'-diphenylmethanediamine (MOCA), 3-5-diethyltoluenediamine (DETDA), and triethanolamine; and / or the physical foaming agent is one or more of HFC-245fa and HFC-141b.

9. The flame retardant polyurethane foam according to any one of claims 1 to 3, characterized in that: The polyisocyanate is one or more of HDI, HMDI, TDI, MDI, PM200, PM400, and PM700.

10. The method for preparing a flame retardant polyurethane foam according to any one of claims 1 to 9, characterized in that: The following steps are involved: 1) Mix component A and keep the temperature at 21-22°C; 2) Material A is mixed with material B which is also kept at a constant temperature of 21-22° C., and poured into a mold to obtain a polyurethane foam product.

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