Polyurea aerogels
Polyurea aerogels as well as methods for preparing the same are disclosed. One method involves mixing a polyisocyanate with a polyamine in a solvent and supercritically drying the resultant gel. Polyoxyalkyleneamine are a preferred type of the polyamines. Other optional steps for the formation of polyurea aerogels include addition of a catalyst, additives, fiber reinforcement, and aging.
1 . A method for preparing a polyurea aerogel comprising the steps of:
mixing an isocyanate or polyisocyanate with a polyoxyalkyleneamine in a solvent, thereby forming a mixture;
allowing the mixture to form a gel; and
supercritically drying the gel.
2 . The method of claim 1 further comprising the step of adding a catalyst to the mixture.
3 . The method of claim 1 further comprising the step of adding an additive to the mixture.
4 . The method of claim 1 further comprising the step of introducing the mixture into a fibrous structure.
5 . The method of claim 1 further comprising the step of aging the gel.
6 . The method of claim 1 wherein said polyoxyalkyleneamine has a molecular weight between about 500 and about 5000.
7 . The method of claim 2 wherein the catalyst is tertiary amine.
8 . The method of claim 3 wherein the additive comprises, an opacifier, chopped fibers, particulates or a combination thereof.
9 . The method of claim 4 wherein the fibrous structure is a felt, mat, batting or a combination thereof.
10 . The method of claim 5 wherein aging is carried out at elevated temperatures.
11 . The method of claim 1 wherein the polyisocyanate is selected from the group consisting essentially of: aliphatic diisocyanates, cycloaliphatic diisocyanates, araliphatic diisocyanates, heterocyclic diisocyanates, aromatic diisocyanates diisocyanates, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 1,4-cyclohexane-diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate, 1-methyl-2,6-cyclohexane diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 2,4′-dicyclohexylmethane diisocyanate, 2,2′-dicyclohexylmethane diisocyanate, toluene 2,4-diisocyanate (TDI), mixtures of toluene 2,4-diisocyanate and toluene 2,6-diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethane diisocyanate, mixtures of 2,4′-diphenylmethane diisocyanate and 4,4′-diphenylmethane diisocyanate, urethane-modified liquid 4,4′-diphenylmethane diisocyanates, 2,4′-di-phenylmethane diisocyanates, 4,4′-diisocyanato-diphenylethane-(1,2), 1,5-naphthylene diisocyanate, triphenylmethane 4,4′,4″-triisocyanate, polymethylene polyphenylene isocyanates (polymeric MDI), any isomeric form of the aforementioned and any mixtures of the aforementioned.
12 . The method of claim 1 wherein the polyoxyalkyleneamine comprises polyoxypropylenediamines, polyoxypropylenetriamines or both.
13 . The method of claim 1 wherein the ratio of the polyoxyalkyleneamine to polyisocyanate is between about 0.01:1 and about 1:1.
14 . The method of claim 1 wherein the ratio of the polyoxyalkyleneamine to polyisocyanate is between about 0.05:1 and about 0.6:1
15 . The method of claim 1 wherein the thermal conductivity of the aerogel is less than about 20 mW/mK.
16 . The method of claim 1 wherein the density of the aerogel is between about 0.01 g/cm 3 and about 0.3 g/cm 3 .
17 . A polyurea aerogel prepared according to the method of claim 1.