Organic aerogels

Details Organic aerogels Organic aerogels

1997-11-20

1999-08-24

Lovering, Richard D.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

252 62, 521128, 521129, 521130, 521155, C08J 912, C08J 914

Patent

active

059425539

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to polyisocyanate based aerogels and to methods for their preparation.
Aerogels are a unique class of ultrafine cell size, low density, open-celled foams. Aerogels have continuous porosity and their microstructure with pore sizes below the free mean path of air (pore sizes in the nanometer range) is responsible for their unusual thermal properties.
Organic aerogels based on polyisocyanate chemistry are described in WO 95/03358.
They are prepared by mixing a polyisocyanate and a trimerisation catalyst and optionally a polyfunctional isocyanate-reactive compound in a suitable solvent and maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel. The gel so formed is then supercritically dried.
During the drying the gel shrinks substantially leading to an increase in density of the obtained aerogel.
Therefore it is an object of the present invention to provide a method for preparing polyisocyanate-based organic aerogels of lower density.
Accordingly, the present invention provides a method for preparing a polyisocyanate based organic aerogel comprising the steps of a) mixing an organic polyisocyanate and an isocyanate trimerisation catalyst and optionally a polyfunctional isocyanate-reactive compound in a suitable solvent, b) maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel, and c) supercritically drying the obtained gel, wherein a filler is mixed with the other ingredients in step a).
The filler used in the process of the present invention is a particulate or fibrous, organic or inorganic material.
Particle sizes of the filler are generally in the range 0.01 to 10 .mu.m, preferably in the range 0.01 to 1 .mu.m and most preferably in the range 0.01 to 0.1 .mu.m.
Examples of suitable fillers to be used in the process of the present invention include talc, carbon black, titanium dioxide, metal flakes, sodium tetraborate, iron oxides, aluminum hydroxide, zinc chloride, magnesium chloride, calcium chloride, ammonium salts, potassium metaphosphate, sulfate salts, carbonates, silicates, silica, clays, polyacrylonitrile beads, polymethylmethacrylate beads, polyvinylchloride beads, polyethylene beads, polycarbonate beads, polyurethane beads, urea beads.
In a preferred embodiment of the present invention the filler used is an infrared absorbing compound, i.e. a compound absorbing (for at least 50%, preferably 75% and most preferably 90%) electromagnetic radiation in the wavelength range 10.sup.-3 to 10.sup.-6 m, especially 2 to 50 .mu.m, more especially 5 to 40 .mu.m and most especially 6 to 20 .mu.m. In this case not only density but also thermal insulation properties of the obtained aerogel are improved.
A preferred filler to be used in the process of the present invention is carbon black. The carbon black may be any of the different kinds available such as lampblack, channel black, gas furnace black, oil furnace black, thermal black and graphitic carbon black. Suitable carbon blacks include furnace black SB250, furnace black SB550 and channel black SB4 (available from Degussa or Cabot).
In the process of the present invention one of such fillers may be used or two or more different fillers may be used.
Typically the amount of the filler used in the process of the present invention ranges from 0.1 to 30%, preferably from 0.5 to 20%, most preferably from 1 to 15% by weight based on the polyisocyanate component.
The filler is usually first dispersed in one of the reaction ingredients such as the polyisocyanate. There may be added compounds which help to disperse the filler or the filler may be surface-treated in order to improve the dispersing.
Aerogels prepared according to the process of the present invention have a lower density (due to a decrease in shrinkage) than those prepared in the absence of a filler.
Densities of the obtained aerogels are generally in the range 1 to 1000 kg/m.sup.3, more generally in the range 10 to 800 kg/m.sup.3 and even more generally in the range 2

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