Aerogel-based material that is super-insulating at atmospheric pressure

Abstract

The present invention relates to a solid thermally insulating material, essentially free of phyllosilicates, comprising (a) from 70 to 98% by volume of hydrophobic silica aerogel particles having an intrinsic density between 110 and 210 kg/m, (b) from 0.3 to 12% by volume of an organic binder formed by at least one organic polymer (b1) and at least one surfactant (b2), or by an amphiphilic organic polymer (b3), these volume fractions being determined by image analysis on thin sections of the solid material and being given relative to the total volume of the material, the aerogel particles having a particle size distribution that has at least two maxima, with a first maximum corresponding to an equivalent diameter (d) of less than 200 m, preferably between 25 m and 150 m, and a second maximum corresponding to an equivalent diameter (D) between 400 m and 10 mm, preferably between 500 m and 5 mm. It also relates to a thermally insulating product containing at least one layer of this material.

Claims

1. A cohesive solid thermal insulation material consisting of: (a) 70% to 98% by volume of hydrophobic silica aerogel particles having an intrinsic density of between 110 and 210 kg/m.sup.3, (b) 0.3% to 12% by volume of an organic binder formed by at least one organic polymer (b1) and at least one surfactant (b2), or by at least one amphiphilic organic polymer (b3), (c) at most 2% by volume of particles which are opacifying under infrared radiation, and (d) a volume fraction of air disposed in the interparticulate space of said cohesive solid thermal insulation material; these volume fractions being determined by image analysis on thin sections of the solid material and being with respect to the total volume of the material, the aerogel particles having a particle size distribution exhibiting at least two maxima, with a first maximum corresponding to an equivalent diameter (d) of less than 200 m and a second maximum corresponding to an equivalent diameter (D) of between 400 m and 10 mm wherein said cohesive solid thermal insulation material presents a thermal conductivity of less than 18 mW/(m.Math.K).

2. The material as claimed in claim 1, wherein the ratio D/d is between 10 and 200.

3. The material as claimed in claim 1, wherein the volume fraction of aerogel particles having an equivalent diameter of less than 200 m, with respect to the total aerogel fraction, is between 7.5% and 60%.

4. The material as claimed in claim 1, wherein the volume fraction of aerogel particles having an equivalent diameter of less than 150 m, with respect to the total aerogel fraction, is between 7.5% and 60%.

5. The material as claimed in claim 1, wherein the volume fraction of aerogel particles having an equivalent diameter of less than 80 m, with respect to the total aerogel fraction, is between 7.5% and 60%.

6. The material as claimed in claim 1, wherein the organic polymer (b1) or the amphiphilic organic polymer (b3) is a thermoplastic organic polymer.

7. The material as claimed in claim 1, wherein the organic polymer (b1) or the amphiphilic polymer (b3) is a thixotropic polymer.

8. The material as claimed in claim 1, wherein the organic polymer (b1) is a thermoset organic resin.

9. The material as claimed in claim 1 exhibiting a density, in the dry state, of between 100 and 215 kg/m.sup.3.

10. A process for the preparation of a solid thermal insulation material as claimed claim 1, comprising: mixing the hydrophobic silica aerogel particles (a) having a particle size distribution exhibiting at least two maxima, with a first maximum corresponding to an equivalent diameter (d) of less than 200 m and a second maximum corresponding to an equivalent diameter (D) of between 400 m and 10 mm the surfactant (b2) and the organic polymer (b1) or the amphiphilic polymer (b3) with, or bringing them into contact with, 0.75 to 4 parts by weight of water, shaping the aqueous composition thus obtained, and drying the shaped material.

11. The process as claimed in claim 10 wherein the hydrophobic silica aerogel (a), before mixing or bringing into contact with the other ingredients, has a compactness of greater than 0.75.

12. The process as claimed in claim 10, wherein the weight ratio of the organic polymer (b1) to the surfactant (b2) is between 30/70 and 80/20.

13. The process as claimed in claim 10, wherein the organic polymer (b1) and the surfactant (b2) or the amphiphilic organic polymer (b3) are first dissolved or dispersed in the water, the solution or dispersion subsequently being mixed or brought into contact with the aerogel particles.

14. The process as claimed in claim 10, wherein the hydrophobic silica aerogel (a) is obtained by mixing at least two aerogel fractions, a first fraction exhibiting a mean equivalent diameter (d.sub.m) of less than 200 m and a second fraction exhibiting a mean equivalent diameter (D.sub.m) of between 400 m and 10 mm.

15. A thermal insulation product comprising at least one layer of a material as claimed in claim 1.

Description

EXAMPLE 1

(1) Two hydrophobic silica aerogels, sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m (Aerogel A, .sub.i=150 kg/m.sup.3, d.sub.m=33.5 m, determined by dry-route laser particle size analysis) for the first and of between 1000 and 1250 m (Aerogel B, .sub.i=182 kg/m.sup.3, D.sub.m=1210 m, determined by dry-route laser particle size analysis) for the second, are mixed.

(2) These aerogels are mixed in different volume proportions and the apparent densities of these mixtures are determined. FIG. 1a thus shows the densities of the mixtures as a function of the fraction by weight of Aerogel B, the complementary part to 100% being formed by Aerogel A.

(3) A mixture of aerogel powders comprising: 40% by weight of particles having a size of less than 100 m (Aerogel A), and 60% by weight of particles having a size of between 1000 and 1250 m (Aerogel B),
has an apparent density (.sub.app) of 0.133 g/cm.sup.3, a compactness of 0.79 (see FIG. 1b) and a thermal conductivity of 16 mW/(m.Math.K) at 23 C.

(4) A volume of this mixture is subsequently mixed with 0.285 volume of a preparation of Bostik adhesive comprising 2.2% by weight of cellulose adhesive sold under the Quelid Vinyl+ brand and 4.2% by weight of a 30% aqueous dispersion of nonionic surfactant sold under the Flip-Flop reference by PCAS.

(5) The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 1 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the wallpaper adhesive to which a surface-active agent has been added (see FIG. 2). A second impregnated sheet is used to cover the paste. This sandwiched structure is allowed to dry, at a temperature of 25 C. and at a relative humidity of 50%, for six days. A product is thus obtained in the form of a self-supporting plate which is easy to handle and to cut up, presented in FIGS. 3 and 4. FIG. 5 shows the microstructure, obtained by X-ray tomography, of the product thus obtained with a magnification of approximately 80.

(6) The conductivity of the layer comprising the aerogel is only 17.0 mW/(m.Math.K) at 23 C., that is to say scarcely greater than that of the powder mixture used for its preparation. This value is spectacularly low in comparison with the thermal conductivities reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 2

(7) Two hydrophobic silica aerogels sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m for the first and of between 1000 and 1250 m for the second, are mixed.

(8) A mixture of aerogel powders comprising: 40% by weight of particles having a size of less than 100 m, and 60% by weight of particles having a size of between 1000 and 1250 m,
has an apparent density (.sub.app) of 0.136 g/cm.sup.3, a compactness of 0.80 and a thermal conductivity of 15.8 mW/(m.Math.K) at 23 C.

(9) A volume of this mixture is subsequently mixed with 0.22 volume of an aqueous preparation comprising 15% by weight of a styrene/butadiene latex dispersion diluted to 47% in water and sold under the Sikalatex brand and comprising 6.2% by weight of a 30% aqueous dispersion of nonionic surfactant sold under the Flip-Flop reference by PCAS. The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 1 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the aqueous preparation. A second impregnated sheet is used to cover the paste. Drying is allowed to take place under a pressure of 0.9 kPa, at a temperature of 40 C. and at a relative humidity of 10%, for 20 h. The paper sheets are withdrawn and a product is thus obtained in the form of a self-supporting plate which is easy to handle and to cut up.

(10) Its conductivity is only 16 mW/(m.Math.K) at 23 C. This value is spectacularly low in comparison with the thermal conductivities reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 3

(11) Opacified hydrophobic silica aerogel, sold under the Isogel name by PCAS/Enersens, is ground and then subjected to fractionation by sieving.

(12) The fraction of particles passing through a 100 m sieve and the fraction obtained between 1000 m and 1250 m are used.

(13) A mixture of opacified aerogel powders comprising: 35% by weight of particles having a size of less than 100 m, and 65% by weight of particles having a size of between 1000 and 1250 m,
has an apparent density (.sub.app) of 0.095 g/cm.sup.3, a compactness of 0.76 and a thermal conductivity of 14.9 mW/(m.Math.K) at 23 C.

(14) A volume of this mixture is subsequently mixed with 0.20 volume of an aqueous preparation comprising 12.7% by weight of a styrene/butadiene latex dispersion diluted to 47% in water and sold under the Sikalatex brand, comprising 4.3% by weight of a 30% aqueous dispersion of nonionic surfactant sold under the Flip-Flop reference by PCAS.

(15) The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 1 cm in a mold, at the bottom of which has been placed a paper sheet impregnated with the aqueous preparation. A second impregnated sheet is used to cover the paste. This sandwiched structure is allowed to dry under a pressure of 0.9 kPa, at a temperature of 40 C. and at a relativity humidity of 10%, for 18 h. The paper sheets are withdrawn and a product is thus obtained in the form of a self-supporting plate which is easy to handle and to cut up.

(16) Its conductivity is only 14.9 mW/(m.Math.K) at 23 C. This value is spectacularly low in comparison with the thermal conductivities reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 4

(17) Two hydrophobic silica aerogels, sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m for the first and of between 1000 and 1250 m for the second, are mixed.

(18) A mixture of aerogel powders comprising: 40% by weight of particles having a size of less than 100 m, and 60% by weight of particles having a size of between 1000 and 1250 m,
has an apparent density (.sub.app) of 0.136 g/cm.sup.3, a compactness of 0.80 and a thermal conductivity of 15.8 mW/(m.Math.K) at 23 C.

(19) A volume of this mixture is subsequently mixed with 0.225 volume of an aqueous preparation comprising 2.1% by weight of a cellulose ether, sold by Tylose under the reference Tylose HA40YP2, and 1.3% by weight of nonionic surfactant, sold by Tylose under the reference Tylovis EP28. The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 1 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the aqueous preparation. A second impregnated sheet is used to cover the paste. This sandwiched structure is allowed to dry, at a temperature of 40 C. and at a relatively humidity of 10%, for 18 hours. A product is thus obtained in the form of a self-supporting plate which is easy to handle and to cut up.

(20) The conductivity of the layer comprising the aerogel is only 15.7 mW/(m.Math.K) at 23 C. This value is spectacularly low in comparison with the thermal conductivities reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 5

(21) Two hydrophobic silica aerogels, sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m for the first and of between 1000 and 1250 m for the second, are mixed.

(22) A mixture of aerogel powders comprising: 40% by weight of particles having a size of less than 100 m, and 60% by weight of particles having a size of between 1000 and 1250 m,
has an apparent density (.sub.app) of 0.136 g/cm.sup.3, a compactness of 0.80 and a thermal conductivity of 15.8 mW/(m.Math.K) at 23 C.

(23) A volume of this mixture is subsequently mixed with 0.24 volume of an aqueous preparation based on a two-component epoxide resin sold by BASF under the reference Mastertop 1720. This preparation comprises 4.9% by weight of the epoxide component Mastertop 1720 A7, 5.22% of the component Mastertop 1720 B7 and 3.95% by weight of a 30% aqueous dispersion of nonionic surfactant sold under the Flip-Flop reference by PCAS. The epoxide components are intimately mixed in a first step before the water and the surfactant are added.

(24) The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 1 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the aqueous preparation. A second impregnated sheet is used to cover the paste. This sandwiched structure is allowed to dry, at a temperature of 40 C. and at a relative humidity of 10%, for 18 hours. A product is thus obtained in the form of a self-supporting plate which is easy to handle and to cut up.

(25) The conductivity of the layer comprising the aerogel is only 16.8 mW/(m.Math.K) at 23 C. This value is spectacularly low in comparison with the thermal conductivities reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 6

(26) Two hydrophobic silica aerogels, sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m for the first and of between 1000 and 1250 m for the second, are mixed.

(27) A mixture of aerogel powders comprising: 30% by weight of particles having a size of less than 100 m, and 70% by weight of particles having a size of between 1000 and 1250 m,
has an apparent density (.sub.app) of 0.129 g/cm.sup.3, a compactness of 0.78 and a thermal conductivity of 16 mW/(m.Math.K) at 23 C.

(28) For a volume of this mixture, mixing with the other components is carried out in two stages. The first stage is a mixing with 0.164 volume of an aqueous solution comprising 1.2% by weight of nonionic surfactant Triton X100 sold by Dow. In the second stage, this combination is mixed with 0.246 volume of an aqueous preparation comprising 14.1% by weight of a dispersion of vinyl/acrylic copolymer, sold by Vinavil under the reference M310 Emulsion, and 1.2% by weight of Triton X100.

(29) The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 1 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the aqueous preparation. A second impregnated sheet is used to cover the paste. 0.05 volume of the liquid phase is subsequently extracted by compressing the paste within this mold. This sandwiched structure is allowed to dry, at a temperature of 40 C. and at a relative humidity of 10%, for 24 hours. A product is thus obtained in the form of a self-supporting plate which is easy to handle and to cut up.

(30) The conductivity of the layer comprising the aerogel is only 17.7 mW/(m.Math.K) at 23 C., that is to say scarcely greater than that of the powder mixture used for its preparation. This value is spectacularly low in comparison with the thermal conductivities reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 7

(31) Two hydrophobic silica aerogels, sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m for the first and of between 1000 and 1250 m for the second, are mixed.

(32) A mixture of aerogel powders comprising: 40% by weight of particles having a size of less than 100 m, and 60% by weight of particles having a size of between 1000 and 1250 m,
has an apparent density (.sub.app) of 0.134 g/cm.sup.3, a compactness of 0.80 and a thermal conductivity of 15.2 mW/(m.Math.K) at 23 C.

(33) In a first step, a volume of this mixture is mixed with 0.44% by weight of polyethylene (PET) fibers with a length of 6 mm. This new mixture is subsequently mixed with 0.21 volume of an aqueous preparation comprising 12% by weight of a dispersion of Model Dispersion latex from BASF diluted to 48% in water comprising 5.7% by weight of a 30% by weight aqueous dispersion of nonionic surfactant, sold under the Flip-Flop reference by PCAS.

(34) The Model Dispersion latex provided by BASF is a styrene/butyl acrylate (sometimes called polystyrenepoly(butyl acrylate)) with a particle size of 210 nm (diameter). It is composed of 44% styrene, 53% butyl acrylate and 3% acrylic acid. The methacrylic acid or PMAA is the steric stabilization system. It is grafted to the surface of the latex particles.

(35) The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 4 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the aqueous preparation. A second impregnated sheet is used to cover the paste. 0.05 volume of the liquid phase is subsequently extracted by compressing the paste within this mold. This sandwiched structure is allowed to dry, at a temperature of 40 C. and at a relative humidity of 10%, for 24 hours. A product is thus obtained in the form of a self-supporting plate which is easy to handle and to cut up.

(36) The conductivity of the layer comprising the aerogel is only 15.9 mW/(m.Math.K) at 23 C., that is to say scarcely greater than that of the powder mixture used for its preparation. This value is spectacularly low in comparison with the thermal conductivity reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 8

(37) Two hydrophobic silica aerogels, sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m for the first and of between 1000 and 1250 m for the second, are mixed.

(38) A mixture of aerogel powders comprising: 40% by weight of particles having a size of less than 100 m, and 60% by weight of particles having a size of between 1000 and 1250 m,
has an apparent density (.sub.app) of 0.133 g/cm.sup.3, a compactness of 0.79 and a thermal conductivity of 16 mW/(m.Math.K) at 23 C.

(39) A volume of this mixture is subsequently mixed with 0.285 volume of an aqueous solution comprising 1.2% by weight of nonionic surfactant Triton X100, sold by Dow, and 2.2% by weight of cellulose adhesive, sold under the Quelid Vinyl+ brand.

(40) The homogeneous composition obtained has the consistency of a paste, which is spread to a thickness of 1 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the aqueous preparation. A second impregnated sheet is used to cover the paste. 0.05 volume of the liquid phase is subsequently extracted by compressing the paste within this mold. This sandwiched structure is allowed to dry, at a temperature of 40 C. and at a relative humidity of 10%, for 24 hours. A product is thus obtained in the form of a self-supporting plate which is fairly easy to handle and to cut up.

(41) The conductivity of the layer comprising the aerogel is only 17 mW/(m.Math.K) at 23 C., that is to say scarcely greater than that of the powder mixture used for its preparation. This value is spectacularly low in comparison with the thermal conductivities reported in the prior art for insulating products based on bonded aerogel particles devoid of phyllosilicates, of between 25 and 350 mW/(m.Math.K).

EXAMPLE 9

Not According to the Invention

(42) Two hydrophobic silica aerogels, sold under the Isogel name by PCAS/Enersens, with particle sizes, established by sieving, of between 0 and 100 m for the first and of between 1000 and 1250 m for the second, are mixed.

(43) A mixture of aerogel powders comprising: 40% by weight of particles having a size of less than 100 m, and 60% by weight of particles having a size of between 1000 and 1250 m, is produced.

(44) This mixture has an apparent density of 0.133 g/cm.sup.3, a compactness of 0.79 and a thermal conductivity of 16 mW/(m.Math.K) at 23 C.

(45) A volume of this mixture is subsequently mixed with 0.27 volume of an aqueous preparation comprising 2.2% by weight of cellulose adhesive, sold under the Quelid Vinyl+ brand of Bostik.

(46) The composition obtained is not very homogeneous. It has the consistency of a paste, which is spread to a thickness of 1 cm in a perforated mold, at the bottom of which has been placed a paper sheet impregnated with the wallpaper adhesive. A second impregnated sheet is used to cover the paste. This sandwiched structure is allowed to dry, at a temperature of 25 C. and at a relative humidity of 50%, for 6 days. A product is thus obtained in the form of a plate which easily breaks when handled.

(47) Evaluation of the Mechanical Properties of the Materials According to with the InventionStudy of the Influence of the Binder:

(48) The mechanical properties of materials according to the invention were evaluated and compared with those of materials not according with the invention. More specifically, four-point bending tests were carried out in order to determine the maximum strength of the material and the strain of the material at this maximum strength.

(49) The bending test is adapted from the standard AFNOR XP-P 18409 for fiber-reinforced concretes.

(50) Prism-shaped test specimens with dimensions of 202080 mm are stressed with a distance between lower supports of A=60 mm and a distance between upper supports of B=20 mm.

(51) The test is carried out on a Bose Electroforce EF3200 device and driven in an open loop with a 22 N cell and an LVDT displacement transducer.

(52) A load/deflection curve is then obtained. This curve exhibits a single maximum which is subsequently used to calculate the maximum stress or strength and the strain at this peak.

(53) The mechanical properties thus determined are shown in the table below. The presented results are the mean of 6 tests.

(54) TABLE-US-00001 Self- Maximum supporting Organic Conductivity strength Strain at plate Surfactant polymer (mW/(m .Math. K)) (kPa) MS (%) According Flip- Quelid 17 50 3.2 to Flop Vinyl+ example 1 cellulose adhesive According Flip- Model 15.9 128 6.0 to Flop Dispersion example 7 latex According Triton Quelid 17 12 2.3 to Vinyl+ example 8 cellulose adhesive According without Quelid 17 2 1 to Vinyl+ example 9 cellulose adhesive

(55) The above results show that the materials according to the invention, such as the materials according to examples 1, 7 and 8, constitute very good insulators and in addition exhibit noteworthy mechanical properties.