POLYURETHANE AEROGELS

Abstract

The present invention relates to a method for preparing a polyurethane foam, in particular an aerogel, from at least one polyisocyanate and at least one optionally recycled polyol, and to the use thereof.

Claims

1. A method for producing a polyurethane (PU) foam, comprising: obtaining a mixture by mixing at least one polyol and at least one first solvent; adding at least one polyisocyanate to the mixture; forming a gel from the mixture; and removing, at least partially, the at least one first solvent from the gel.

2. The method according to claim 1, wherein the foam has a porosity of 55-99 percent (%).

3. The method of claim 1, wherein the polyurethane contains urethane groups and one or more of or mixtures of isocyanurate groups, carbodiimide groups, allophanate groups, urea groups, uretdione groups, iminooxadiazinedione groups, or uretonimine groups.

4. The method of claim 1, wherein the polyol has a total hydroxyl number of 50-600 mg KOH/g, measured according to ASTM E 1899-80.

5. The method of claim 1, wherein the at least one polyol is obtainable by aminolysis or alcoholysis of plastics comprising monomers comprising at least one polyol.

6. The method of claim 1, wherein the at least one first solvent is selected from one or more of or mixtures of acetone, ethyl acetate, dimethyl sulfoxide, acetonitrile, or ethanol.

7. The method of claim 1, wherein adding the at least one polyisocyanate to the mixture comprises adding a solution of the at least one polyisocyanate and at least one additional solvent to the mixture.

8. The method of claim 1, wherein the polyisocyanate has a total isocyanate content of 25-40 percent (%).

9. The method of claim 1, further comprising rinsing the gel with at least one second solvent.

10. A polyurethane foam obtained by a method comprising: obtaining a mixture by mixing at least one polyol and at least one first solvent; adding at least one polyisocyanate to the mixture; forming a gel from the mixture; and removing, at least partially, the at least one first solvent from the gel.

11. The method of claim 1, wherein the at least one polyol has a viscosity greater than 60,000 millipascal-seconds (mPas), measured according to DIN 53019 at 25 degrees Celsius (° C.).

12. The method of claim 1, wherein the PU foam is one of an absorbent, an adsorbent, a thermal insulator, a lightweight filler or in a composite material.

13. The method of claim 1, further comprising separating solids from the first mixture.

14. The method of claim 1, wherein obtaining the second mixture further comprises adding at least one adjuvant to the first mixture.

15. The method of claim 1, further comprising at least partially replacing the at least one solvent with at least another solvent that is different from the at least one solvent, wherein removing the at least one solvent further comprises removing the at least another solvent.

16. The method of claim 1, wherein the at least one polyol comprises at least one recycled polyol.

17. The method of claim 5, wherein the aminolysis or alcoholysis comprises methanolysis or glycolysis.

18. The method of claim 5, wherein the plastics comprise wastes of polyurethane, polyisocyanurate, polycarbonate, polylactide, polyhydroxyburate or polyester.

19. The method of claim 7, wherein the solution further comprises at least one adjuvant, wherein the at least one adjuvant comprises a catalyst.

20. The method of claim 8, wherein the polyisocyenate is selected from selected from aliphatic, cycloaliphatic or aromatic polyisocyanates.

21. The method of claim 8, wherein the polyisocyenate comprises one or more of or a mixture of hexamethylene diisocyanate, isophorone diisocyanate, methylene-bis(4-cyclohexyl isocyanate), 2,4-cyclohexyl isocyanate, 2,6-cyclohexyl diisocyanate, toluene diisocyanate (TDI), (polymeric) diphenylmethane diisocyanate (MDI), naphthylene-1,5-diisocyanate (NDI), or 4,4′,4″-triisocyanate triphenylmethane.

22. The method of claim 11, wherein the at least one polyol has one or more of (A) a water content of less than or equal to 0.50 percent (%) measured according to DIN 51777 or (B) an acid number less than or equal to 0.50 mg KOH/g measured according to the manufacturer's instructions Metrohm Application Bulletin No. 200/2 d.

Description

EXAMPLE 1: PRODUCTION OF A RECYCLED POLYOL

[0071] For the production of a recycled polyol, non-homogenous polyurethane chips from the production of polyurethane sheets were degraded by glycolysis. For this purpose, about 10 wt % glycol and 0.2 wt % metal catalyst, based on the amount of polyurethane waste used, were placed in a reaction vessel and heated to about 210° C. Subsequently, the polyurethane waste was added successively under constant stirring. After complete addition, the reaction was stirred at constant temperature for two hours. The reaction mixture was filtered to separate coarse insoluble fractions.

[0072] The obtained recyclate had a residual content of 80-90 wt %, an acid number of <0.50 mg KOH/g, a water content of <0.50%, and a viscosity of >200,000 mPas at 25° C.

EXAMPLE 2: PREPARATION OF A POLYURETHANE FOAM

[0073] 4.17 g of the recycled polyol obtained in Example 1 were dissolved in 0.73 mol acetone. To the solution, 3.17×10.sup.−4 mol of catalyst (1,4-diazabicyclo[2.2.2]octane dissolved in dipropylene glycol) was added with stirring. MDI was then added with stirring at 4.8 vol % (relative to acetone). Gel formation was carried out while resting in a closed reaction vessel at room temperature for at least 60 min, after which the obtained gel was supercritically dried at 50° C. and 120 bar.

[0074] The obtained PU foam had a porosity of 85%.

EXAMPLE 3: PREPARATION OF A POLYURETHANE FOAM

[0075] 1.92 g of the recycled polyol obtained in Example 1 was dissolved in 0.77 mol acetone. To the solution, 0.001 mol of catalyst (1,4-diazabicyclo[2.2.2]octane dissolved in dipropylene glycol) was added with stirring. In the following, 4 vol % (relative to the acetone) MDI was added under stirring. Gel formation was carried out while resting in a closed reaction vessel at room temperature for 40 min, after which the obtained gel was atmospherically dried to conditions of 20° C. and 1 bar.

[0076] The obtained PU foam had a porosity of 90%, a specific inner surface area of about 160 m.sup.2/g and an average pore diameter of 20 nm.

[0077] The following items are subject-matter of the present invention: [0078] 1. A method for producing a polyurethane foam comprising the steps: [0079] (i) mixing at least one polyol and at least one solvent L1, [0080] (ii) optionally separating solids from the mixture obtained in step (i), [0081] (iii) adding at least one polyisocyanate and optionally at least one adjuvant to the mixture obtained in step (i) or (ii), [0082] (iv) forming a gel from the mixture obtained in step (iii), [0083] (v) optionally at least partially replacing the at least one solvent L1 by at least one solvent L2, and [0084] (vi) at least partially removing the at least one solvent L1 and/or L2. [0085] 2. The method according to item 1, wherein the foam has a porosity of 55-99%, preferably 75-90%. [0086] 3. The method according to item 1 or 2, wherein the foam has a density of 100-500 kg/m.sup.3, preferably of 120-350 kg/m.sup.3, more preferably of 120-250 kg/m.sup.3. [0087] 4. The method according to any one of the preceding items, wherein the specific inner surface area of the foam is 50-500 m.sup.2/g, preferably 100-300 m.sup.2/g and/or the mean pore diameter is less than 500 nm, preferably less than 150 nm, more preferably 10-100 nm and/or the cumulative pore volume fraction is at least 0.25 cm.sup.3/g, preferably 0.3-3.0 cm.sup.3/g and/or the thermal conductivity is less than 75 mW/mK, preferably 12-55 mW/mK and more preferably 16-35 mW/m K. [0088] 5. The method according to any one of the preceding items, wherein the foam is an aerogel. [0089] 6. The method according to any one of the preceding items, wherein the polyurethane contains, in addition to urethane groups, isocyanurate, carbodiimide, allophanate, urea, uretdione, iminooxadiazinedione, uretonimine groups or mixtures thereof. [0090] 7. The method according to any one of the preceding items, wherein the polyol has a total hydroxyl number of 50-600 mg KOH/g, preferably 100-300 mg KOH/g measured according to ASTM E 1899-80. [0091] 8. The method according to any one of the preceding items, wherein the polyol has a total viscosity greater than 60,000 mPas, preferably greater than 100,000 mPas, more preferably greater than 200,000 mPas measured according to DIN 53019 at 25° C. [0092] 9. The method according to any one of the preceding items, wherein the polyol is obtainable by alcoholysis, in particular methanolysis or glycolysis, or aminolysis of plastics based on monomers comprising at least one polyol, in particular wastes of polyurethane, polyisocyanurate, polycarbonate, polylactide, polyhydroxyburate or polyester. [0093] 10. The method according to any one of the preceding items, wherein the solvent L1 is selected from acetone, ethyl acetate, dimethyl sulfoxide, acetonitrile, ethanol and mixtures thereof. [0094] 11. Method according to any one of the preceding items, wherein the mixture obtained in step (i) is subjected to filtration, decantation or centrifugation in step (ii). [0095] 12. The method according to any one of the preceding items, wherein the mixture obtained in step (i) or (ii) is added in step (iii) to a solution of at least one polyisocyanate, at least one solvent L3 and optionally at least one adjuvant. [0096] 13. The method according to item 11, wherein the solvent L3 is identical to the solvent L1. [0097] 14. The method according to any one of items 12-13, wherein the at least one adjuvant is selected from catalysts, stabilizers, cell regulators such as surfactants, flame retardants, fillers, or mixtures thereof. [0098] 15. The method according to item 14, wherein the at least one adjuvant comprises at least one catalyst selected from organic amines, transition metal catalysts, alkali metal catalysts, or mixtures thereof. [0099] 16. The method according to any one of the preceding items, wherein the polyisocyanate has a total isocyanate content of 25-40%, preferably 27-35%, more preferably 30.5-32.5%. [0100] 17. The method according to any one of the preceding items, wherein the polyisocyanate is selected from aliphatic, cycloaliphatic or aromatic polyisocyanates, in particular hexamethylene diisocyanate, isophorone diisocyanate, methylene-bis(4-cyclohexyl isocyanate), 2,4-cyclohexyl isocyanate, 2,6-cyclohexyl diisocyanate, toluene diisocyanate (TDI), (polymeric) diphenylmethane diisocyanate (MDI), naphthylene-1,5-diisocyanate (NDI), 4,4′,4″-triisocyanate triphenylmethane, and mixtures thereof. [0101] 18. The method according to any one of the preceding items, wherein step (iv) takes place at temperatures from 20-70° C., preferably 20-50° C. [0102] 19. The method according to any one of the preceding items, wherein step (iv) takes place in a solvent-gas atmosphere, preferably in a closed system. [0103] 20. The method according to any one of the preceding items, wherein step (iv) takes place in a mold, in particular in a closed mold. [0104] 21. The method according to any one of the preceding items, wherein in step (v) the gel obtained in step (iv) is rinsed with at least one solvent L2. [0105] 22. The method according to any one of the preceding items, wherein the solvent L2 comprises liquid or supercritical CO.sub.2. [0106] 23. The method according to any one of the preceding items, wherein step (vi) is carried out by depressurizing or evaporating the solvent L1, L2 and/or L3 at elevated temperature, preferably at 25-70° C. [0107] 24. Polyurethane foam obtainable by a method according to any one of items 1-23. [0108] 25. A use of a polyol, in particular a recycled polyol, having a viscosity of >60,000 mPas, preferably >100,000 mPas, more preferably >200,000 mPas measured according to DIN 53019 at 25° C. and optionally a water content of ≤0.50% measured according to DIN 51777 and/or an acid number of ≤0.50 mg KOH/g measured according to the manufacturer's instructions Metrohm Application Bulletin No. 200/2 d for the preparation of a polyurethane foam, in particular a polyurethane aerogel. [0109] 26. The use of the polyurethane foam according to item 24 as an absorbent, adsorbent, thermal insulator, lightweight filler or in a composite material.