Process for producing porous alginate-based aerogels
The present invention relates to a process for preparing a porous material, at least comprising the steps of providing a mixture (I) comprising a water soluble polysaccharide, at least one compound suitable to react as cross-linker for the polysaccharide or to release a cross-linker for the polysaccharide, and water, and preparing a gel (A) comprising exposing mixture (I) to carbon dioxide at a pressure in the range of from 20 to 100 bar for a time sufficient to form a gel (A), and depressurizing the gel (A). Gel (A) subsequently is exposed to a water miscible solvent (L) to obtain a gel (B), which is dried. The invention further relates to the porous materials which can be obtained in this way and the use of the porous materials as thermal insulation material, for cosmetic applications, for biomedical applications or for pharmaceutical applications.
1. A porous material obtained by a process comprising:
a) providing a mixture (I) comprising
(i) a water soluble polysaccharide,
(ii) a compound which reacts as a cross-linker for the water soluble polysaccharide or which releases a cross-linker for the water soluble polysaccharide, and
(iii) water;
b) preparing a gel (A) by a process comprising
b1) exposing the mixture (I) to carbon dioxide at a pressure of from 20 to 100 bar for a time sufficient to form a gel (A), and
b2) depressurizing the gel (A);
c) exposing the gel (A) to a water miscible solvent (L) to obtain a gel (B); and
d) drying the gel (B),
wherein the water miscible solvent (L) is at least one selected from the group consisting of a C1 to C6 alcohol a C1 to C6 ketone, and a mixture thereof,
wherein the water soluble polysaccharide is an alginate, and wherein the compound which reacts as a cross-linker for the water soluble polysaccharide or which releases a cross-linker for the water soluble polysaccharide in the mixture (I) comprises calcium carbonate,
wherein the porous material has a pore volume in the range of from 2.1 to 9.5 cm 3 /g for pore sizes <150 nm.
2. The porous material of claim 1 , wherein the preparing in b) is carried out at a temperature of from 10 to 40° C.
3. The porous material of claim 1 , wherein carbon dioxide in the exposing in b1) is gaseous.
4. The porous material of claim 1 , wherein a water insoluble solid (S) is further added to the mixture (I).
5. The porous material of claim 1 , wherein a compound (C) is further added to the mixture (I) in the providing in a), wherein the compound (C) is at least one selected from the group consisting of a natural hydrocolloid forming polymer, a synthetic hydrocolloid-forming polymer, and a mixture thereof.
6. The porous material of claim 1 , wherein the exposing in c) is carried out at a pressure of from 10 to 100 bar.
7. The porous material according to claim 1 , wherein the drying in d) is carried out by converting a liquid in the gel (B) into a gaseous state at a temperature and a pressure below a critical temperature and a critical pressure of the liquid in the gel (B).
8. The porous material according to claim 1 , wherein the drying in d) is carried out under supercritical conditions.
9. A cosmetic, biomedical, or pharmaceutical product, comprising:
a thermal insulation material comprising the porous material of claim 1 .