SELF-COOLING COMPOSITE MATERIALS

Abstract

The present invention relates to a composite material which comprises at least one thermoresponsive polymer and at least one inorganic building material. The present invention further relates to a method for producing the composite material and also to the use of the composite material for cooling and for regulating the humidity.

Claims

1. A composite material which comprises the components (A) at least one thermoresponsive polymer and (B) at least one inorganic building material, the composite material further comprising a component (C), at least one clay mineral, wherein the component (C) is not a binder, the component (A) having a lower critical solution temperature (LCST), the lower critical solution temperature (LCST) being in the range from 5 to 70 C., and the component (B) being selected from the group consisting of hydraulically setting binders and nonhydraulically setting binders, wherein the composite material comprises in the range from 5 to 45 wt % of component (A), in the range from 10 to 94.9 wt % of component (B), and in the range from 0.1 to 45 wt % of component (C), based in each case on the sum of the weight percentages of components (A), (B), and (C).

2. The composite material according to claim 1, wherein component (A) is selected from the group consisting of poly(meth)acrylates, poly(meth)acrylamides, poly(meth)acryloylpyrrolidines, poly(meth)acryloylpiperidines, poly-N-vinylamides, polyoxazolines, polyvinyloxazolidones, polyvinylcaprolactones, polyvinylcaprolactams, polyethers, hydroxypropylcelluloses, polyvinyl ethers, and polyphosphoesters.

3. The composite material according to claim 1, wherein component (C) is selected from the group consisting of montmorillonites and kaolinites.

4. The composite material according to claim 1, wherein the composite material comprises in the range from 10 to 40 wt % of component (A), in the range from 20 to 89.5 wt % of component (B), and in the range from 0.5 to 20 wt % of component (C), based in each case on the sum of the weight percentages of components (A), (B), and (C).

5. The composite material according to claim 1, wherein the composite material comprises at least one component (D), at least one organic binder.

6. A method for producing a composite material according to claim 1, comprising the steps of a) providing a mixture (M) which comprises the at least one thermoresponsive polymer component (A), b) mixing the mixture (M) with component (B) to give the composite material, wherein the mixture (M) provided in step a) further comprises at least one clay mineral component (C).

7. The method according to claim 6, wherein the providing of the mixture (M) in step a) comprises a polymerization of at least one monomer selected from the group consisting of (meth)acrylates, (meth)acrylamides, (meth)acryloylpyrrolidines, (meth)acryloylpiperidines, N-vinylamides, oxazolines, vinyloxazolidones, vinylcaprolactones, vinylcaprolactams, alkylene oxides, vinyl ethers, and phosphoesters, to give the at least one thermoresponsive polymer component (A).

8. The method according to claim 6, wherein the providing of the mixture (M) in step a) comprises the following steps: a1) providing a first dispersion which comprises the at least one clay mineral component (C), a dispersion medium selected from the group consisting of water and an organic solvent, and at least one monomer selected from the group consisting of (meth)acrylates, (meth)acrylamides, (meth)acryloylpyrrolidines, (meth)acryloylpiperidines, N-vinylamides, oxazolines, vinyloxazolidones, vinylcaprolactones, vinylcaprolactams, alkylene oxides, vinyl ethers, and phosphoesters, a2) polymerizing the at least one monomer present in the first dispersion provided in step a1), in the first dispersion, to give the at least one thermoresponsive polymer component (A), to give a second dispersion which comprises the at least one clay mineral component (C), the dispersion medium, and the at least one thermoresponsive polymer component (A), a3) drying the second dispersion obtained in step a2) to give the mixture (M).

9. The method according to claim 6, wherein the providing of the mixture (M) in step a) comprises a spray drying of the at least one thermoresponsive polymer component (A) in the presence of the at least one clay mineral component (C).

10. The method according to claim 6, wherein the mixture (M) provided in step a) comprises the at least one thermoresponsive polymer component (A) in the form of particles and comprises the at least one clay mineral component (C) in the form of particles, the particles of the at least one thermoresponsive polymer component (A) having a D50 in the range from 200 nm to 5 mm, and the particles of the at least one clay mineral component (C) having a D50 in the range from 50 nm to 3 mm, determined by light scattering and/or sieving.

11. A method comprising utilizing the composite material according to claim 1 for at least one of cooling buildings, interiors, electrical assemblies, primary batteries or secondary batteries, outdoor facilities, and exterior facades, and regulating the humidity in interiors of buildings by applying the composite material thereon or incorporating the composite material therein.

Description

EXAMPLES

[0244] Preparation of a Mixture (M) from Components (A) and (C)

[0245] The following components were used:

Monomers:

[0246] N-Isopropylacrylamide (NiPAAm) from Wako Chemicals and from TCI Chemicals [0247] N,N-Methylenebisacrylamide (BIS) from AppliChem and Merck KGaA [0248] [3-(Methacryloylamino)propyl]trimethylammonium chloride solution (MAPTAC; 50 wt % in water) from ABCR GmbH

Clay Mineral:

[0249] Sodium bentonite: EXM757 from Sd-Chemie

Initiators:

[0250] N,N,N,N-Tetramethylethylenediamine (TEMEDA) from ABCR GmbH [0251] Potassium peroxodisulfate (KPS) from Fluka [0252] Ammonium peroxodisulfate (APS) from Grssing GmbH Analytica

[0253] Sodium bentonite (162 g, 113 mmol of sodium) was swollen in deionized water (2 l). Then further deionized water was added, giving the dispersion a volume of 12 liters in total. NiPAAM (1000 g, 8840 mmol), BIS (50 g, 324 mmol, 5 wt % based on NiPAAM), and MAPTAC (50 g of a 50 wt % strength solution in water, 113 mmol, 5 wt % based on NiPAAM) were added to the dispersion, to give the first dispersion. After devolatilization with nitrogen, the first dispersion was heated to 80 C. and KPS (20 g, 74 mmol, 2 wt % based on NiPAAM) was added in order to initiate the polymerization of the monomers. The polymerization was carried out at 80 C. for 6 hours. After cooling had taken place, 5 liters of deionized water were added in order to reduce the viscosity of the resulting second dispersion. The particles of the mixture (M) present in the second dispersion had a diameter in the range from 1 to 2 mm. The water fraction of the second dispersion was 90 wt %, based on the overall weight of the second dispersion.

[0254] The second dispersion was subsequently dried by different methods.

a) Spray Drying of the Second Dispersion

[0255] Spray drying was carried out using a Nubilosa LTC-ME laboratory spray dryer. The entry temperature was set at 165 C., the exit temperature was regulated at 85 to 90 C. by means of the injected second dispersion. The second dispersion was atomized with compressed air (5 bar) through a two-component nozzle (diameter 2 mm). The residual moisture content of the resulting mixture (M) was 3 wt %. The mixture (M) obtained by spray drying is referred to below as (M-S).

b) Centrifugation and Subsequent Drying at Room Temperature

[0256] The resulting second dispersion was centrifuged at 4200 rpm in a CEPA LS laboratory centrifuge with a polyamide filter bag. The resulting mixture was subsequently dried at room temperature for 5 days and finally ground. The residual moisture content of the mixture (M) obtained was 6 wt %. The mixture (M) obtained by centrifugation and subsequent drying at room temperature is referred to below as (M-C).

[0257] In order to determine the morphology of the particles present in M-S and M-C, the particles were analyzed by environmental scanning electron microscopy (ESEM 2020 from ElectroScan), equipped with a GSED (gaseous secondary electron detector). The results are shown in FIGS. 1a and 1b for (M-S) and 2a and 2b for (M-C).

[0258] It can be seen that significantly smaller particles having a diameter of around 100 m are obtained by the spray drying (FIGS. 1a and 1b), in comparison to centrifuged and subsequently dried particles, whose diameter is around 300 m (FIGS. 2a and 2b). The particles of the clay mineral are disposed on the surface of the thermoresponsive polymer.

Composite Material

[0259] The composite material and the comparative materials were produced using the following components:

Mixture (M):

[0260] M-S (spray-dried)

Component (B)

[0261] B-a: Portland cement, CEM I 52.5, from Schwenk, Mergelstetten [0262] B-b: Cement mortar: 11 g Portland cement, 32.9 g sand aggregate (EN 196-1 standard sand) and 6.1 g water [0263] B-c: Gypsum binder: 50 g -hemihydrate gypsum binder (Knauf A4FF AHH), 45 g water and 0.3 g Starvis S 3911 F (BASF) stabilizer/thickener [0264] B-d: Geopolymer mortar: 11.1 g metakaolin (Metamax, BASF SE), 25 g silica sand BCS 319 (Strobel Quarzsand GmbH), 14 g potassium silicate K45 M (Woellner, Ludwigshafen) and 6 g water

[0265] To produce a composite material comprising component B-a, the dry mixture (M) was mixed with the dry component B-a, followed by addition of water, further thorough mixing, the introduction of the mixture into a circular wooden mold with a diameter of 4 cm and a height of 2 cm, and the curing of the composite material at room temperature for 24 hours. The material was then removed from the mold and the disks were surface-polished on both sides to a thickness of 1 cm. These circular disks were used as sample specimens in the measurements described below.

[0266] The amounts of component B-a, water and the mixture (M) used are reported in table 1.

TABLE-US-00001 TABLE 1 Component (A) Cement M-S based on (B-a) Water M-S [wt % composite Example [g] [ml] [g] based on cement] material (wt %) V1 30 15 0 V2 30 15 0.3 1 0.9 V3 30 20 1.5 5 4.2 B4 30 50 3.0 10 7.9 B5 24 55 7.9 30 21.6 B6 20 60 10 50 29.1 B7 15 60 9.0 60 32.7 B8 7.5 60 5.6 75 37.3 V18 7.5 60 8.5 113 46.3 V19 6 60 10 167 54.5

[0267] The sample specimens produced as described above were first of all weighed, then introduced into deionized water and, after 2 hours and also after 24 hours, removed and weighed. The water absorption, determined as an average value from four measurements, corresponded to the weight increase after drip-drying of the sample specimens, minus the original dry weight of the sample. The water content of the sample specimens was then calculated relative to the total weight of the sample, in wt %.

[0268] The water content of the various sample specimens is reported in table 2.

TABLE-US-00002 TABLE 2 Water content after 2 h Water content after 24 h [wt. %] [wt. %] V1 22 33 V2 23 36 V3 28 45 B4 35 50 B5 51 75 B6 54 72 B7 52 70 B8 50 66

[0269] For assessing the suitability of the composite materials for cooling, especially of buildings, the rate of absorption of water and therefore the water content after 2 hours are of great importance. Suitable materials for cooling must absorb an extremely large amount of water within a short time in order to be able to be employed efficiently for cooling.

[0270] It is evident that the comparison materials in comparative examples V1 to V3 exhibit a much lower water absorption than the inventive composite materials of examples B4 to B8. It is also evident that the rise in the water content after two hours correlates with the fraction of the mixture (M) in the composite material, and that a maximum in the absorption capacity is achieved in the case of examples B5 and B6.

[0271] The composite materials of comparative examples V18 and V19 were not dimensionally stable, and disintegrated on swelling in water. No useful shaped articles were obtained, therefore.

Passive Cooling

[0272] For determination of the passive cooling behavior, the sample specimens produced as described above were placed at an angle of 40 and at a distance of 35 cm from an infrared lamp (500 W halogen). A constant stream of air was passed over the sample specimens at a flow rate of 0.1 m/s. An infrared camera was used to determine the temperature profile on the surface of the materials.

[0273] In order to determine the change in water content, the sample specimens were placed on a balance and the weight of the sample specimens was determined as a function of time.

[0274] In order to determine the cooling effect of the materials, the sample specimens were each placed on a cut-to-size panel of a rigid polyurethane foam material (Kingspan Therma TF70 insulated flooring panel, dimensions 1010 cm, thickness 3 cm) and, between the panel of rigid polyurethane foam material and the sample specimen, a thermocouple was introduced, which determines the temperature on the reverse of the sample specimen.

a) Surface Temperature and Water Content

[0275] The surface temperatures and also the water content of the composite material of example B6 and of the comparison material of comparative example V1 were determined over a period of 300 minutes. The initial water content of the samples (72 wt % for B6 and 33 wt % for V1; see table 2) was set at 100% in each case, and the percentage decrease in weight of both samples over time was monitored.

[0276] FIG. 3 shows the results of this test.

[0277] It can be seen that at the start of the measurement, the rate of evaporation of the water is identical in both examples B6 and V1. After about 30 minutes, however, already more water has evaporated from the composite material of example B6. Over the entire measurement period, more water evaporates from the composite material of example B6 than from the comparison material of comparative example V1, and so a smaller percentage water content is left in the case of example B6. At the same time, owing to the greater rate of evaporation, the inventive composite material B6 exhibits a lower surface temperature and hence a greater cooling effect. The higher cooling effect of the composite material of the invention derives from the fact that it is able to take up greater amounts of water, but then also gives up this water again more willingly. This effect is much less pronounced in the comparison material, where, additionally, the water is given up less willingly to the surrounding environment.

b) Passive Cooling

[0278] For the determination of the passive cooling behavior, the surface temperature of the different composite materials was determined over a period of 530 minutes. Prior to measurement, all of the samples were swollen in deionized water for 24 hours (see table 2).

[0279] At the start of measurement, the surface temperature of all the materials increases very sharply. After 90 minutes the material of comparative example V1 has a temperature of around 55 C., while the inventive composite materials exhibit only a temperature of around 33 C. up to a maximum of 38 C. In the case of the inventive composite materials, this temperature is maintained for 60 to 170 minutes. The cooling effect, in other words the duration of the holding of the temperature in the range from 33 to a maximum of 38 C., correlates directly with the fraction of mixtures (M) in the composite materials. The plateau at the lowest temperature is obtained for example B5.

c) Two-Layer Measurements

[0280] The two-layer measurements were conducted as described above. FIG. 5 shows the surface temperature (O) and also the reverse temperature (R) of the composite material B4 and of the comparison material V1 over the measuring period of 960 minutes.

[0281] It is evident that not only the surface temperature but also the reverse temperature of the inventive composite material B4 are much lower than the respective temperatures of the comparison material V1. With the inventive composite material, therefore, a higher cooling effect is obtained than with the comparison material.

Passive Cooling Behavior of Composite Materials Comprising Components B-b to B-d

[0282] For producing a composite material comprising components B-b to B-d, the dry mixture (M) was mixed with the dry component B-b, B-c or B-d. The amount of mixture (M) added in each case was such that the composite material contained 10 wt % of the mixture (M), based on component B. Thereafter water was added, the constituents were mixed thoroughly, the mixture was introduced into a wooden mold having a diameter of 4 cm and a height of 3 cm, and the composite material was cured for 12 hours at room temperature and 65% humidity and also for a further 12 hours at 50 C. in a drying cabinet. The composite materials were subsequently removed from the mold, and the disks were surface-polished on both sides to a thickness of 2 cm. These disks were used as sample specimens in the measurements described below.

[0283] The sample specimens were first of all weighed, then placed in deionized water and, after 24 hours, taken out and weighed again. The water absorption, determined as the average value from four measurements, corresponded to the weight increase after drip-drying of the sample specimens, minus the original dry weight of the sample. The water content of the sample specimens was then calculated in relation to the total weight of the sample, in wt %.

[0284] The composition of the composite materials and water content after 24 h are reported in table 3.

TABLE-US-00003 TABLE 3 M-S Water content after 24 h Example Component B [wt %] [wt %] V9 Cement mortar (B-b) 0 7.5 B10 Cement mortar (B-b) 10 33.6 V11 Gypsum binder (B-c) 0 60.5 B12 Gypsum binder (B-c) 10 90.3 V13 Geopolymer mortar (B-d) 0 21.9 B14 Geopolymer mortar (B-d) 10 36.1

[0285] Here as well it is evident that comparison materials V9, V11 and V13 exhibit a much lower water absorption than the inventive composite materials of examples B10, B12 and B14.

[0286] The composite materials were additionally investigated for their passive cooling behavior. For this purpose, holes with a diameter of 39 mm were punched from an Aerogel panel measuring 40402 cm and having a low thermal conductivity (0.019 W/mK, Slentex Aerogel, BASF Polyurethanes GmbH), and the sample specimens of composite materials B10, B12 and B14 and also the comparative sample specimens V9, V11 and V13 were introduced into the holes. The surface of the experimental arrangement was lit with a 500 W halogen lamp and the underside was observed with an infrared camera for determination of the reverse temperatures. Before being introduced into the aerogel, the composite materials were swollen completely in water for 24 hours as described above. The lighting time was 300 minutes; the temperatures on the reverse of specimens V9 and B10, V11 and B12 and V13 and B14 were determined at the end of the measurement time, and a calculation made of the temperature difference between the pairs of values. At the end of the measurements, the inventive composite materials had the lower reverse temperatures in each case. The results can be seen in table 4.

TABLE-US-00004 TABLE 4 Temperature Sample specimens difference Example in comparison ( C.) B15 V9-B10 6.4 B16 V11-B12 5.6 B17 V13-B14 2.1