METHOD FOR PRODUCING ORGANICALLY MODIFIED AEROGELS

Abstract

The invention relates to a method for producing organically modified aerogels. The problem addressed by the invention is that of providing an economical method for producing hydrophobic aerogels which can be implemented cost-effectively, simply, and safely, and which operates to save on resources. This problem is solved by the provision of a method for producing organically modified aerogels, wherein a sol containing [SiO.sub.4,2] units is produced, and the sol obtained is dispersed in a continuous phase. The sol forms a separate phase and the continuous phase contains at least 20 wt % organosiloxane, a gel is formed from the sol in the continuous phase, and the gel obtained is surface-modified in the presence of a phase mediator in the continuous phase, wherein acids or chlorosilanes or mixtures thereof are added as initiator and the gels obtained are dried. The aerogels provided can be used as insulating materials, in particular in thermal insulation.

Claims

1. A method for producing organically modified aerogels, said method comprising the following steps: i. preparing a sol comprising [SiO.sub.4/2] units, ii. dispersing the sol in a continuous phase where the sol forms a separate phase and the continuous phase comprises not less than 20 wt % of organosiloxane, iii. forming a gel from the sol in the continuous phase, iv. surface modifying the gel in a presence of a compatibilizer in the continuous phase where acids or chlorosilanes or mixtures thereof are admixed as initiator, and v. drying the gel obtained in step iv.

2. The method as claimed in claim 1, wherein the organosiloxane is a disiloxane of the formula R.sub.3SiOSiR.sub.3, where each R may be the same or different and is hydrogen or a substituted or unsubstituted organic moiety.

3. The method as claimed in claim 1, wherein the compatibilizer is admixed in the step of preparing the sol or is formed therefrom.

4. The method as claimed in claim 1, wherein alcohols are used as the compatibilizer.

5. The method as claimed in claim 1, wherein step iv takes place without a solvent exchange beforehand.

6. The method as claimed in claim 1, wherein the initiator consists of trimethylchlorosilane or hydrochloric acid or mixtures thereof.

7. The method as claimed in claim 2, wherein the disiloxane used is hexamethyldisiloxane.

8. The method as claimed in claim 4, wherein ethanol is used as the compatibilizer.

9. The method as claimed in claim 1, wherein not more than 20 g of the initiator are used per 100 g of gel.

10. The method as claimed in claim 1, wherein the surface-modifying step (step iv) is conducted at a temperature from 40 to 80 C.

11. The method as claimed in claim 1, wherein duration of the surface-modifying step (step iv) is below 5 hours.

12. The method as claimed in claim 1, wherein tetraethoxysilane (TEOS) or water glass or hydrolysis products thereof are used as [SiO.sub.4/2] starting material.

13. The method as claimed in claim 2, wherein the compatibilizer is admixed in the step of preparing the sol or is formed therefrom.

14. The method as claimed in claim 13, wherein alcohols are used as the compatibilizer.

15. The method as claimed in claim 14, wherein step iv takes place without a solvent exchange beforehand.

16. The method as claimed in claim 15, wherein the initiator consists of trimethylchlorosilane or hydrochloric acid or mixtures thereof.

17. The method as claimed in claim 16, wherein the disiloxane used is hexamethyldisiloxane.

18. The method as claimed in claim 17, wherein ethanol is used as the compatibilizer.

19. The method as claimed in claim 18, wherein not more than 20 g of the initiator are used per 100 g of gel.

20. The method as claimed in claim 19, wherein the surface-modifying step (step iv) is conducted at a temperature from 40 to 80 C.

21. The method as claimed in claim 20, wherein a duration of the surface-modifying step (step iv) is below 5 hours.

22. The method as claimed in claim 21, wherein tetraethoxysilane (TEOS) or water glass or hydrolysis products thereof are used as [SiO.sub.4/2] starting material.

Description

EXAMPLES

[0095] Applicable to all examples:

[0096] tetraethyl orthosilicate (WACKER TES28 from Wacker Chemie AG), water glass (Sigma-Aldrich: SiO.sub.2 content: 26.5 wt %, Na.sub.2O content: 10.6 wt %), hexamethyldisiloxane (WACKER AK 0.65 SILICONOEL from Wacker Chemie AG), trimethylchlorosilane (SILAN M3 from Wacker Chemie AG).

[0097] All other laboratory chemicals were obtained from Sigma-Aldrich.

Example 1

[0098] A round-bottom flask was initially charged with 210 ml of water and 1.0 ml of 1 M hydrochloric acid, followed by heating to 50 C. Under agitation by intensive stirring, 104 g of TEOS were admixed by stirring at 50 C. for one hour.

[0099] In a second flask, 700 ml of hexamethyldisiloxane were heated to 60 C. and intensively stirred.

[0100] The sol was intensively stirred while being admixed with 12.5 ml of 0.25 M ammonia solution and transferred within a minute into the second round-bottom flask holding the HMDSO. The reaction mixture was stirred at 60 C. for 3 hours. Then, 30 g of concentrated hydrochloric acid (corresponds to 9.1 g of hydrochloric acid per 100 g of gel) were admixed with stirring and the reaction mixture was stirred at 60 C. Every 15 minutes, the stirrer was stopped, the phase separation awaited (1 minute) and the volume of the displaced, aqueous phase (bottom phase) was marked. After 90 minutes, the displacement of the aqueous pore liquid was complete, i.e., the volume of the aqueous phase was maximal and did not change any further. The gel particles were subsequently separated off by filtration using a Bchner funnel (Whatman Filter, 125 mm, Grade 40).

[0101] The gel particles were finally dried in a vacuum drying cabinet (10 mbar, 120 C.). The following values were determined as described in the analytical methods:

[0102] bulk density: 0.07 g/cm.sup.3

[0103] BET: 748 m.sup.2/g

[0104] BJH pore volume: 4.3 cm.sup.3/g

[0105] median pore diameter: 17 nm

Example 2

[0106] In a glass beaker, 150 g of water and 150 g of water glass (Aldrich: SiO.sub.2 content: 26.5 wt %, Na.sub.2O content: 10.6 wt %) were mixed and cooled to 10 C. in an ice bath.

[0107] In a second glass beaker, 100 g of hydrochloric acid (7.5 wt %) were initially charged, cooled to 10 C. in an ice bath and stirred at 500 rpm with a magnetic stirrer.

[0108] The cooled water glass solution was gradually added via a dropping funnel to the hydrochloric acid solution with stirring. Care was taken with the rate of addition that the temperature does not exceed 10 C. The admixture was stopped at pH 3.2 and 22 g of ethanol were admixed as compatibilizer. The liquid sol was subsequently subjected to intensive stirring (KPG stirrer, 700 rpm) while being transferred into a mixture of 550 ml of hexamethyldisiloxane containing 1.0 g of the water glass solution as base and stirred at 60 C. for 3 hours. Then, the dispersion was heated to 80 C., admixed with 23 g of trimethylchlorosilane (corresponds to 10 g of TMCS per 100 g of gel) under agitation by stirring and further stirred at 70 C. Every 15 minutes, the stirrer was stopped, the phase separation awaited (1 minute) and the volume of the displaced, aqueous phase was marked. After 120 minutes, the displacement of the aqueous pore liquid was complete. The gel particles were subsequently separated off by filtration using a Bchner funnel (Whatman Filter, 125 mm, Grade 40) and dried to constant weight under reduced pressure in a vacuum drying cabinet (10 mbar, 120 C.)

[0109] bulk density: 0.10 g/cm.sup.3

[0110] BET: 500 m.sup.2/g

[0111] BJH pore volume: 3.2 cm.sup.3/g

[0112] median pore diameter: 22 nm

Example 3

[0113] A round-bottom flask was initially charged with 210 ml of water and 1.0 ml of 1 M hydrochloric acid, followed by heating to 50 C. Under agitation by intensive stirring, 104 g of TEOS were admixed by stirring at 50 C. for one hour.

[0114] In a second flask, 700 ml of an HMDSO solution (50 wt %) in n-hexane were heated to 60 C. and intensively stirred.

[0115] The sol was intensively stirred while being admixed with 12.5 ml of 0.25 M ammonia solution and transferred within a minute into the second round-bottom flask holding the HMDSO solution. The reaction mixture was stirred at 60 C. for 3 hours. Then, 30 g of concentrated hydrochloric acid (corresponds to 9.1 g of hydrochloric acid per 100 g of gel) were admixed with stirring and the reaction mixture was stirred at 60 C. Every 15 minutes, the stirrer was stopped, the phase separation awaited (1 minute) and the volume of the displaced, aqueous phase was marked. After 3 hours, the displacement of the aqueous pore liquid was complete.

[0116] The gel particles were subsequently separated off by filtration using a Bchner funnel (Whatman Filter, 125 mm, Grade 40).

[0117] The gel particles were finally dried in a vacuum drying cabinet (10 mbar, 120 C.). The following values were determined as described in the analytical methods:

[0118] bulk density: 0.08 g/cm.sup.3

[0119] BET: 760 m.sup.2/g

[0120] BJH pore volume: 4.0 cm.sup.3/g

[0121] median pore diameter: 17 nm

Comparative Example 1

[0122] A round-bottom flask was initially charged with 210 ml of water and 1.0 ml of 1 M hydrochloric acid, followed by heating to 50 C. Under agitation by intensive stirring, 104 g of TEOS were admixed by stirring at 50 C. for one hour.

[0123] In a second flask, 700 ml of hexamethyldisiloxane were heated to 60 C. and intensively stirred.

[0124] The sol was intensively stirred while being admixed with 12.5 ml of 0.25 M ammonia solution and transferred within a minute into the second round-bottom flask holding the HMDSO. The reaction mixture was stirred at 60 C. for 3 hours. The gel particles were subsequently separated off by filtration using a Buchner funnel (Whatman Filter, 125 mm, Grade 40). To remove the ethanol, the gel pieces were incubated in hot distilled water (300 ml of water per 100 g of gel) at 60 C. five times for 24 hours at a time. The incubating water was decanted off after 12 hours in each period, to then be replaced by fresh water. The gel particles were subsequently dispersed in 700 ml of hexamethyldisiloxane, heated to 60 C. and admixed with 30 g of concentrated hydrochloric acid (corresponds to 9.1 g of hydrochloric acid per 100 g of gel) by stirring. Every 15 minutes, the stirrer was stopped, the phase separation awaited (1 minute) and the volume of the displaced, aqueous phase was marked. After 3 hours, no separate aqueous phase could be made out. The reaction mixture was stirred at 60 C. for a further 16 hours, after which a separate aqueous phase could still not be made out, i.e., no silylation had taken place.

Comparative Example 2

[0125] Example 2 was repeated except that the admixture of the compatibilizer (ethanol) into the sol was omitted. No separate aqueous phase could be made out even after 24 hours.

Comparative Example 3

[0126] A round-bottom flask was initially charged with 210 ml of water and 1.0 ml of 1 M hydrochloric acid, followed by heating to 50 C. Under agitation by intensive stirring, 104 g of TEOS were admixed by stirring at 50 C. for one hour.

[0127] In a second flask, 700 ml of n-hexane were heated to 60 C. and intensively stirred.

[0128] The sol was intensively stirred while being admixed with 12.5 ml of 0.25 M ammonia solution and transferred within a minute into the second round-bottom flask holding the n-hexane. The reaction mixture was stirred at 60 C. for 3 hours. Then, 30 g of concentrated hydrochloric acid (corresponds to 9.1 g of hydrochloric acid per 100 g of gel) were admixed with stirring and the reaction mixture was stirred at 60 C. Every 15 minutes, the stirrer was stopped, the phase separation awaited (1 minute) and the volume of the displaced, aqueous phase was marked. After 3 hours, no separate aqueous phase could be made out. The reaction mixture was stirred at 60 C. for a further 16 hours, after which a separate aqueous phase could still not be made out.

Comparative Example 4

[0129] In a screw-lidded jar, an initial charge of 210 ml of water and 1.0 ml of 1 M hydrochloric acid was heated to 50 C. Under agitation by intensive stirring (magnetic stirrer 500 rpm), 104 g of TEOS were admixed and stirred in at 50 C. for one hour. This was followed by the admixture of 12.5 ml of 0.25 M ammonia solution, subsequent stirring for one minute and finally removal of the stirrer. The gel obtained was stored in a sealed vessel in a drying cabinet at 60 C. for 3 hours. Subsequently, the gel was pressed through a sieve having a mesh size of 5 mm in order to obtain pieces below 5 mm in size. The gel pieces were introduced into a screw flask together with 700 ml of hexamethyldisiloxane and heated to 60 C. Then, 30 g of concentrated hydrochloric acid (corresponding to about 9.1 g of hydrochloric acid per 100 g of gel) were admixed, the flask was shaken, and the volume of the displaced aqueous phase was noted every 15 minutes. It took 1.5 hours before a separate aqueous phase could be identified. The displacement of the pore liquid took 4 hours to complete.