Insulating composite materials comprising an inorganic aerogel and a melamine foam

Abstract

The invention relates to insulating composite materials comprising an inorganic aerogel and a melamine foam. The invention also relates to the production method of said materials, and to the use of same.

Claims

1. A composite comprising an inorganic aerogel reinforced by an open-cell melamine foam, wherein said composite has a thermal conductivity λ between 10 and 20 mW/m-K measured using a guarded hot plate according to NF EN 12667 at 20° C. and atmospheric pressure, a percentage of a volume occupied by macropores, macropores being pores with a diameter greater than 10 μm, in a volume occupied by the composite in its entirety is less than 5%, the inorganic aerogel is non-granular, and the inorganic aerogel has a continuous three-dimensional porous structure.

2. Composite according to claim 1, produced by a process comprising the following successive steps: a) casting an inorganic sol in a reactor in which was previously placed the open-cell melamine foam, b) gelation of the sol into a lyogel, c) drying the lyogel.

3. Composite according to claim 1, wherein the aerogel is formed from an inorganic sol comprising between 5% and 15% by weight of inorganic material based on the total weight of the inorganic sol.

4. Composite according to claim 1, wherein macropores whose diameter is between 50 and 250 microns comprises more than 80% of total number of macropores of said composite.

5. Composite according to claim 1, wherein the composite has a thickness of between 2 and 50 nm.

6. Composite g to claim 1, wherein the composite has a density between 70 kg/m.sup.3 and 150 kg/m.sup.3.

7. Composite according to claim 1, wherein the melamine foam is a melamine-formaldehyde foam having a thickness of between 2 and 50 mm, a porosity of between 95% and 99.5%, a density between 8.5 and 11.5 kg/m3, and a thermal conductivity of between 35 and 40 mW/m-K measured using a guarded hot plate according to NF EN 12667 at 20° C. and atmospheric pressure.

8. Composite according to claim 1, wherein the inorganic aerogel comprises silica, titanium oxide, manganese oxide, calcium oxide, carbonate calcium, zirconium oxide, or mixtures thereof.

9. Composite according to claim 1, wherein the composite does not contain any binder.

10. Composite according to claim 9, wherein the composite does not comprise a fibrous reinforcing material.

11. Composite according to claim 1, wherein the composite has a quantity of residual solvent by weight of the composite of less than or equal to 3% according to EN/ISO 3251.

12. Composite according to claim 1, wherein the aerogel further comprises an opacifier.

13. A sandwich panel comprising at least one layer consisting essentially of a monolithic composite according to claim 1.

14. A multilayer thermal insulation panel comprising at least one layer of a composite according to claim 1.

15. Acoustic insulation comprising at least one layer of a composite according to claim 1.

16. Composite according to claim 1, wherein composite has a thermal conductivity λ between 12.5 and 20 mW/m-K at 20° C. and atmospheric pressure.

17. Composite according to claim 1, wherein less than 5% of the volume occupied by the composite is occupied by pores with a diameter greater than 5 μm.

18. Composite according to claim 1, wherein the inorganic aerogel is in the form of a single block piece.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1: Distribution of the macropore volume measured by X-ray tomography in three dimensions (3D) on the composite material obtained in Example 1. The x-axis represents the volume in mm.sup.3 (on a scale of 0 to 0.01 mm.sup.3) and the y-axis represents the number of macropores (on a scale from 0 to 250). The mean pore volume (Vm) for a vast majority of the material was between 1.Math.10.sup.−4 mm.sup.3 and 5.Math.10.sup.−3 mm.sup.3.

(2) FIG. 2: A diagram showing the three-point bending device for measuring the flexibility modulus of a material. The panel is placed on two supports (represented by triangles) located at 7.5 cm from the edge, and spaced 10 cm apart, and a vertical downward force is applied by positioning the various weights (represented by a sphere in the Figure) placed at the center of the material. The distance from the center of deformation of the material is measured.

(3) FIG. 3: Curve representing the force (measured in Newton (N), y-axis) as a function of the flex (measured in mm, x-axis). This curve represents the test results of Example 3. Linear regression is used to determine a slope of 0.0385 N/mm, and an intercept of 0.

(4) FIG. 4: Representation of the test results of Example 4. The curve obtained represents the conventional stress (expressed in MPa) as function of the relative deformation, ∈=(e−e.sub.0)/e.sub.0, with e.sub.0 as the sample thickness before the test, and ∈ being without units.

(5) The examples which follow are intended to further illustrate the present invention but are in no way limiting.

EXAMPLES

Example 1

Preparation of a Composite Panel of Thickness 10 mm According to the Invention

(6) 1) Preparation of a Silica Alcogel Composite

(7) A silica sol obtained by hydrolyzing alkoxysilane in the presence of hydrochloric acid and then adding ammonia, was poured before gelation on a 250×290×10 mm.sup.3 sheet of melamine foam (Basotect foam marketed by BASF) in a closed chamber 300×300×70 mm.sup.3 in dimensions. After gelling, the reinforced alcogel was aged for 24 hours at 50° C. in ethanol. Hydrochloric acid and hexamethyldisiloxane (hydrophobing agent) were then introduced into the chamber to completely cover the composite alcogel. The reaction medium was heated and maintained at 50° C. for 48 h. The reaction mixture was separated from the hydrophobic silica alcogel composite by percolation.

(8) 2) Production of a Composite Material Comprising Melamine Foam and Hydrophobic Silica Aerogel

(9) The condensed alcogel reinforced by the melamine foam sheet was dried in a ventilated oven at 160° C. for 2 hours. The aerogel panel obtained is 10 mm thick and has a thermal conductivity of 12.6 mW/m-K, measured by means of guarded hot plate of NF EN 12667 at 20° C. and atmospheric pressure.

(10) 3) Measurement of Pore Diameter and Macroporosity

(11) The composite material obtained after drying is then analyzed by 3D X-ray tomography. The acquisitions were made with DeskTom machine model equipped with a 130 kV generator. The resolution obtained on the sample is 24.5 μm, with a source/sample distance of about 12 cm. The software used for the acquisition and reconstruction of the data is a software developed by RX Solutions: X-Act. For post-processing (visualization and analysis of porosity), the software VG Studio Max Version 2.2 was used.

(12) Analysis showed the pore volume (Vm) for a vast majority of the material is between 1.Math.10.sup.−4 mm.sup.3 and 5.Math.10.sup.−3 mm.sup.3 (see FIG. 1).

(13) Considering that the pore shape can be likened to a perfect sphere, we apply the following mathematical formula:

(14) $d_{\mathrm{mayen}}=\sqrt{\left(\frac{6\times V_{\mathrm{mayen}}}{\pi }\right)}.$
The diameter of the material is thus calculated as between 57 and 212 μm.

(15) The macroporosity of the sample is calculated as the integral of the ratio of the pore volumes identified in the sample volume. According to this calculation method, the composite material has a macroporosity of 1.44%.

Example 2

Preparation of a Composite Panel of Thickness 30 mm According to the Invention

(16) 1) Preparation of a Composite of Silica Alcogel

(17) A silica sol obtained by hydrolyzing alkoxysilane in the presence of hydrochloric acid and then adding ammonia was poured prior to gelling onto a 250×290×30 mm.sup.3 sheet of melamine foam in a closed chamber with dimensions of 300×300×70 mm.sup.3. The solvent used was ethanol. After gelation, the reinforced alcogel was aged for 24 hours under a reflux of ethanol. Hydrochloric acid and hexamethyldisiloxane (hydrophobing agent) were then introduced into the chamber to completely cover the composite alcogel. The reaction medium was heated and maintained at reflux in ethanol for 48 h. The reaction mixture was separated from the hydrophobic silica alcogel by percolation.

(18) 2) Obtaining a Melamine Foam Panel and Hydrophobic Silica Aerogel Composite

(19) The reinforced hydrophobic silica alcogel was placed in a microwave dryer and dried for 50 min at 50° C.

(20) The obtained aerogel panel was 30 mm thick and had a thermal conductivity of 14.2 mW/m-K, measured by means of guarded hot plate of NF EN 12667 at 20° C. and atmospheric pressure.

Example 3

Measurement of Flexibility of the Composite Material According to Example 1

(21) A 3-point bending test was performed as shown in FIG. 2 on a 25×10×250 mm.sup.3 sample of material manufactured according to the method presented in Example 1. The composite material is placed on two supports separated by 100 mm.

(22) Different forces are applied to the sample at its center. The displacement (flex) thereof was measured.

(23) Results:

(24) The results obtained are shown in FIG. 3. The stiffness or flexural rigidity was calculated as K=0.0385 N/mm, which corresponds to the slope of the force-deflection curve.

Example 4

Measurement of Maximum Compression Stress of a Composite Material According to Example 1

(25) A uniaxial compression test was performed on an electromechanical testing machine Zwick 100 kN, provided with an external force sensor capacity of 5 kN.Math.D dimensions of the sample were 30×30×10 mm.sup.3. The moving crosshead speed is 0.3 ram/min during load and 1 mm/min during discharge.

(26) The results of this test are shown in FIG. 4. A compression modulus of 0.43 MPa was measured, and a maximum stress of 3.3 MPa with a relative deformation of 80%.

Example 5

Preparation of a Composite Insulating Foam Panel 10 mm Thick According to the Invention

(27) 1) Preparation of a Silica Hydrogel Composite

(28) A silica sol obtained by mixing an aqueous solution of sodium silicate and hydrochloric acid solution, was poured before gelation on a 250×290×10 mm.sup.3 sheet of melamine foam in a closed chamber having dimensions of 300×300×70 mm.sup.3. After gelling, the reinforced hydrogel was aged for 24 hours at 50° C. in water. A solvent exchange was carried out with acetone (for 48 h at 50° C. by recycling acetone two times). Hydrochloric acid and hexamethyldisiloxane (hydrophobing agent) were then introduced into the chamber so as to completely cover the composite lyogel. The reaction medium was heated and maintained at 50° C. for 48 h. The reaction medium as separated from the hydrophobic silica lyogel by percolation.

(29) 2) Obtaining a Composite Panel Comprising Melamine Foam and Hydrophobic Silica Xerogel

(30) The condensed lyogel reinforced by the sheet of melamine foam was dried in a ventilated oven at 160° C. for 2 hours. The xerogel panel obtained was 9 mm thick and has a thermal conductivity of 14.5 mW/m-K, measured by means of guarded hot plate of NF EN 12667 at 20° C. and atmospheric pressure.

(31) It is noted that the panels according to Examples 1, 2 and 5 all comprise between 92% and 98% of aerogel by weight based on the weight of the composite.

(32) In all the above examples, ammonia is used as a gel catalyst (step b) in an amount between 2 and 2.5% by weight relative to the total weight of the sol starting components.