DE102014218931A1 - Sandwich structure with an airgel-containing core material - Google Patents

Abstract

The present invention relates to a core material comprising a carrier material with macroscopic cavities in which the cavities are filled with an airgel and a sandwich structure comprising the core material.

Description

The present invention relates to a core material comprising a carrier material with macroscopic cavities in which the cavities are filled with an airgel and a sandwich structure comprising the core material.

Composite materials or fiber composite materials are increasingly being used in vehicle construction, in particular in aircraft construction, because of their high rigidity and strength and their comparatively low weight. Sandwich structures are used in particular because of their high flexural rigidity in these areas. A sandwich structure usually consists of a moderately shear-resistant core material, which is connected to two external, stretch-resistant cover layers in a shear-resistant and tension-resistant manner. As the core material is usually a lightweight material, which is suitable for increasing the distance between the two outer layers used. In this case, the cover layers can each be resistant to bending. Due to their structure sandwich structures are very well suited to endure bending loads. The tensile and compressive loads occurring due to the bending are maximal in the cover layers. Ideally, they should therefore be very stiff and firm. The core material is loaded on thrust and pressure.

Known core materials usually consist mainly of foams or aramid, aluminum, polypropylene, paperboard, polyacryletherketone, thermoplastic Polymethacrylemid-, polyvinyl chloride, thermoset polyurethane ware or balsa end grain. Honeycomb core materials are in part capable of absorbing higher mechanical forces compared to foam core materials without creeping and have better fatigue resistance. In addition, honeycombs are particularly light and yet have good mechanical properties.

To obtain a rigid and dimensionally stable core material, the honeycomb structure can be filled with spherical or fibrous fillers, the fillers being bonded together at their points of contact with a binder, as described, for example, in US Pat DE 10 2011 082 087 A1 is described.

In case of fire, however, known sandwich structures quickly have a low stability. The matrix material and often the binder begin to decompose thermally from temperatures of about 200 ° C, so that the structure has no stability after a short time.

One way to protect a sandwich structure in case of fire is to choose a flame retardant matrix system. Phenol-formaldehyde resins are often used here. Although these have good fire behavior, they are clearly inferior to other systems in terms of their mechanical properties. Another possibility is to add different flame retardants to the matrix system. Here, for example, materials are used, which release water in case of fire and so cool the material and dilute the flue gases. These additives must often be added in very large proportions by weight and thus lead to an increase in weight and often also to embrittlement of the material. Another possibility is the application of flame-retardant layers or paints. These can expand up to 200 times under the influence of heat and thus form a barrier layer, which impedes the heat conduction and the mass transfer.

A composite material with a low weight core material and at the same time suitable for fire protection is known in DE 10 2004 046 495 A1 described. Here, a hydrophobic airgel is mixed with an inorganic binder and an inorganic hydrophilic dispersant. The binder is cement, gypsum, lime, loam, waterglass and / or clay. As a dispersant, for example, ammonium fluoride can be used. The composite material described there can be used on the one hand as a structural element in buildings. The airgel particles impart thermal insulation properties to the material and also allow fire protection.

With known from the prior art, fire-resistant composites usually the mechanical property of the sandwich structure are deteriorated. Frequently, the weight of the composite also increases, so that use, in particular in aircraft construction, is no longer possible. Paints which are used as a fire retardant can flake off, so that no flame retardant effect is present.

The object of the present invention is therefore to provide a core material which overcomes the above-mentioned disadvantages.

The object underlying the present invention is achieved by a core material 1 from a carrier material with macroscopic cavities, in which the cavities are filled with an airgel.

In a further embodiment, the present invention relates to a sandwich structure 3 , which is the core material according to the invention 1 includes, wherein the core material 1 between two cover layers 2a . 2 B is arranged. An appropriate structure is shown schematically in 1 shown.

An inventive core material 1 can be prepared by a method which is characterized in that the carrier material macroscopic cavities, in which an aerosol solution is introduced as a filler and the aerosol solution is then dried without shrinkage in the carrier material to form an airgel. This gives the core material according to the invention 1 from a carrier material with macroscopic cavities in which the cavities are filled with an airgel.

Aerogels are highly porous solids, the bulk of which consists of pores. As a material they have been known for decades. They are characterized by unique properties such as low density, very high specific surface area, low thermal conductivity and high acoustic impedance.

Silica-based aerogels are widely used, ie inorganic aerogels. In addition, organic aerogels are known. These are prepared, for example, based on resorcinol and formaldehyde, melamine and formaldehyde, phenol and furfural, cresol and formaldehyde, polymerizable isocyanates, phenol and melamine or polyvinyl chlorides. A peculiarity of these purely organic aerogels is that they can be converted by pyrolysis into carbon aerogels, whereby the structure of the aerogels is preserved.

The synthesis of aerogels is typically done by a sol-gel process. The drying of the resulting gel is supercritical or subcritical, depending on the preparation process and starting materials.

Before the resulting gel is dried, the aerosol solution, ie the colloidal sol, is introduced into the macroscopic cavities of the carrier material. Only on site, so in the carrier material, the aerosol solution is brought to dry. The drying takes place without shrinkage, so that the airgel obtained adheres firmly to the substrate.

According to the invention, known from the prior art, organic or inorganic aerosol solutions can be used. The core material 1 thus comprises organic or inorganic aerogels in the cavities of the support material. Preferably, the core material 1 from an organic or inorganic airgel and the carrier material.

Inorganic aerosol solutions must be dried under supercritical conditions to allow shrinkage-free drying. In contrast, organic aerogell solutions, in particular resorcinol-formaldehyde aerogell solutions, can be dried even under subcritical conditions. In particular, the preparation and drying of organic aerogell solutions is described in detail in the prior art, such as in the not yet published DE 10 2013 216 965 , Inorganic aerosol solutions are preferred in view of their properties as a fire retardant in a corresponding application. In view of a simple, inexpensive manufacturing process, organic aerosol solutions are preferred.

Both inorganic and organic aerogell solutions enable the production of an insulating core material. In this case, both an acoustic insulation (sound insulation) and a thermal insulation (thermal insulation, cold insulation) is possible.

In this case, the core material according to the invention 1 Surprisingly, a high flexural strength. The flexural strength of the core material according to the invention is about 1.7 times higher than the flexural strength of the pure airgel. The core material according to the invention thus not only enables insulation, but also increases the stability in a structure in which it is used.

As carrier material, known carrier materials, such as open-cell / open-cell foams or a honeycomb structure can be used. Preferably, a honeycomb structure is used. According to the invention, the honeycomb structure can be paper honeycomb, honeycomb cardboard, aluminum honeycomb, aramid honeycomb or Act polymer honeycombs. The advantage of the honeycomb structure is that they are widespread and therefore cost-effective and can be obtained from different materials. The disadvantage is that a thermal bridge is present through the webs of the honeycomb structure. However, this disadvantage is outweighed by the advantages which result from the airgel as a filler of the cavities of the carrier material, such as low weight and good insulation.

A honeycomb structure, like other support materials with macroscopic cavities, usually has two open sides through which a liquid can flow. If, for example, a liquid is applied to the first open side of the carrier material, it flows out of the second open side. So that this does not occur according to the invention when introducing the aerosol solution, a first material layer is preferably applied to the first open side of the carrier material prior to the introduction of the aerosol solution. If the carrier structure is placed on a surface which prevents the aerosol solution from flowing through, but from which the aerosol solution or the subsequently cured airgel can be easily removed, it is not necessary to apply a layer of material prior to introducing the aerosol solution. Such a material layer is not necessary even if the support structure is immersed in the aerosol solution, whereby the aerosol solution is also introduced into the cavities of the support structure. Frequently, carrier structures, in particular honeycomb structures, already have a material layer on one side due to their production method, as a result of which an open side is already closed. In this case, the application of a further layer of material is unnecessary.

If, before introducing the aerosol solution, the first open side of the carrier material is not covered with a layer of material, this can also take place after the aerosol solution has been dried. Furthermore, after drying the aerosol solution, a material layer can also be applied to the second open side, which lies opposite the first open side of the carrier material. This layer of material on the second open side of the substrate may be the same as the first layer of material. However, it is also possible to apply mutually different material layers. An inventive core material 1 can thus have a layer of material on the opposite open sides.

The materials which are applied as a material layer to the open sides of the carrier structure may be, for example, filters made of fleece or paper.

The method allows a complete filling of the cavities of the carrier material with an airgel obtained after drying. So that the carrier material is completely covered with the airgel and there are no cavities, it is possible to carry out the introduction of the aerosol solution into the carrier structure under the influence of ultrasound. Ultrasonically, any gas bubbles present are carried out of the carrier material or the aerosol solution.

A stable and compact core material 1 To obtain, it may also be necessary to match the hydrophobicity or hydrophilicity of the carrier material with that of the airgel or the aerosol solution. The material adhesion of the airgel can be tested for example on a film which consists of the same material as the carrier material. In particular, by varying the pH of the aerosol solution, the adhesion of the airgel with the carrier material can be adjusted and improved.

Furthermore, it is possible to provide the carrier structure with a coating before introducing the aerosol solution. This coating is tailored to the hydrophobicity or hydrophilicity of the aerosol solution and thereby enables improved adhesion between airgel and support structure. Here the core material covers 1 then a coated support structure and an airgel.

Hydrophobic in the sense of the present invention means that the material shows a contact angle of more than 90 ° with respect to water at room temperature (25 ° C.). Hydrophilic materials exhibit a corresponding contact angle of less than 90 ° with respect to water.

With the aid of the described method, a core material is obtained 1 from a carrier material with macroscopic cavities, in which the cavities are completely filled with an airgel.

The carrier material preferably comprises a honeycomb structure, in particular a paper honeycomb, honeycomb honeycomb, aluminum honeycomb, aramid honeycomb or polymer honeycomb structure. The cavities of the carrier material may be filled with an organic or inorganic airgel known from the prior art. Organic aerogels, more preferably resorcinol-formaldehyde aerogels are present as a filler in the cavities, since they can be dried even under subcritical conditions, which allows good adhesion with the substrate. If the core material according to the invention 1 are used in particular in fire protection, it is preferred that the airgel is an inorganic airgel, since this is still stable even at higher temperatures.

The three-dimensional network structure of the dried airgel preferably consists of particles of a size of less than 5 μm, in particular of less than 3 μm, particularly preferably the particle size is in the range of 100 nm to 3 μm. Small particles allow a particularly good, as complete as possible filling of the cavities of the support structure. The size of the particles is determined by scanning electron micrographs (SEM).

The core material according to the invention 1 preferably has a density in the range of 0.1 to 0.3 g / cm ³ and / or a thermal conductivity in the range of 0.04 to 0.06 W / mK. The low density and the low thermal conductivity make it possible to use it as a fire protection material, which can also be used in areas in which a low weight is needed.

An inventive core material 1 is part of a sandwich structure in a further embodiment of the invention 3 , In this case, the core material 1 between two cover layers 2a . 2 B arranged. 1 shows schematically the structure of a sandwich structure according to the invention 3 ,

The two cover layers 2a . 2 B may be the same or different. Are the two cover layers 2a . 2 B different from each other, so can the sandwich structure 3 a bearing skin as one of the top layers 2a . 2 B and an outer skin as one of the other two cover layers 2a . 2 B include. Between the supporting skin and the outer skin a flame-retardant core is arranged. This core is the core material according to the invention 1 , The core material is used here 1 as a spacer between the two cover layers 2a . 2 B , Due to its low weight, the weight of the sandwich structure according to the invention 3 kept low overall. Due to the low thermal conductivity of the core material 1 , When heat is applied to one of the cover layers, the second cover layer is not thermally stressed. In case of fire, therefore, the top layer, which is not directly exposed to the fire, through the core material 1 protected.

A method for producing a sandwich structure according to the invention 3 includes the following steps:
Providing the core material 1 which comprises a carrier material and an airgel, and
Laminating the core material 1 with the cover layers 2a . 2 B such that the core material 1 between the cover layers 2a . 2 B is arranged.

The lamination of the core material 1 with the cover layers 2a . 2 B can be done, for example, by first applying an adhesive layer to the core material 1 is applied, which then the actual material of the cover layer 2a . 2 B is applied. However, it is preferred that a prepreg material, which comprises both an adhesive layer and the actual cover layer, directly on the core material 1 is applied.

The cover layers 2a . 2 B are preferably selected from fiber-reinforced plastics, such as CFRP (carbon fiber reinforced plastic), GFRP (glass fiber reinforced plastic), AFK (aramid fiber reinforced plastic) or NFK (natural fiber reinforced plastic), or metals such as aluminum or titanium.

According to the invention, it is possible that the sandwich structure 3 not just a core material 1 comprising, which is between two cover layers 2a . 2 B located. According to the invention it is also possible that to one of the two outer layers 2a . 2 B another core material 1 connects, which in turn with another cover layer 2a . 2 B is provided. This results in a layer structure in which core material 1 and one covering layer each 2a . 2 B alternate with each other. The resulting composite material closes on the outer layers each with a cover layer 2a . 2 B from.

In a preferred embodiment, the sandwich structure according to the invention 3 from a core material according to the invention 1 as well as two outer layers 2a . 2 B , where the core material 1 between the cover layers 2a . 2 B is arranged.

Is on the core material 1 applied a layer of material, the result is a layer structure of the first cover layer 2a , Material layer, core material 1 , Material layer, second cover layer 2 B , The two layers of material can, as well as the outer layers, be the same or different from each other.

Due to the airgel as part of the core material 1 or the sandwich structure 3 the material has thermally insulating properties. In addition, the weight is low. This allows the use of the sandwich structure 3 as a component in land, water and / or aircraft, such as cars, airplanes and / or trains. For example, the sandwich structure 3 be used as an outer skin in an aircraft. By the then increased heat insulation of the outer skin insulating material could be saved and aircraft could thus be lighter and thus more energy efficient. The same applies to other vehicles in which the core material produced according to the invention 1 or the sandwich structure 3 Use finds.

EXAMPLES

Embodiment 1

• Preparing the solution:

First, 127.4 g of deionized water (W) was weighed in a beaker. Thereafter, 50.0 g of resorcinol (R) were added, the solution was stirred at room temperature until the resorcinol had completely dissolved (5 to 7 min). Thereafter, 76.8 g of formaldehyde (F) (24 wt% solution) were added thereto and stirred for a further 5 min. Next, 0.032 g of Na ₂ CO ₃ ^© (solid) was added to the solution. After stirring for a further 5 minutes, the pH was adjusted with dilute nitric acid. The pH of the solution was adjusted to 5.7. The solution was stirred for another 20 min at room temperature.

After preparation in each case a piece HexWeb ^® Hexcel, Welkenraedt, Belgium was added with a size of 3.0 × 3.0 cm in approximately 13 mL resorcinol-formaldehyde solution. HexWeb ^® is a phenolic resin coated aramid honeycomb.

Composition of the aerosol solution (ratios of constituents):

• R / C 1500; R / F 0.74; R / W 0.044

• Gelation:

The aramid honeycomb solutions were packed in sealed polypropylene containers and allowed to gel in oven at 80 ° C for two days.

• Dry:

The gel was dried at 80 ° C for 24 hours. The result is honeycombs that are completely filled with RF airgel. The honeycomb material is wetted almost perfectly, which can be seen from the scanning electron micrograph in 2 can be seen.

Embodiment 2:

Coating of cardboard with RF airgel

• – Reihe 1: Pappe wurde direkt nach dem Rühren für 30 bis 300 Sekunden (s) eingetaucht;
• – Reihe 2: RF-Lösung wurde bei 80°C für 30 Min in Ofen gehalten, dann wurde Pappe für 30 bis 300 s eingetaucht;
• – Reihe 3: RF-Lösung wurde bei 80°C für 60 Min in Ofen gehalten, dann wurde Pappe für 30 bis 300 s eingetaucht.

An aerosol solution was prepared as in Embodiment 1, having the following composition: R / F = 0.74; R / C = 1500; R / W = 0.044. The pH of the solution was adjusted to 5.62. The solution was stirred for 20 min. Cardboard was then immersed in this RF solution for different dipping times at different times. The size of the cardboard samples was about 4 cm × 4 cm.

• - Row 1: Cardboard was dipped immediately after stirring for 30 to 300 seconds (s);
• Row 2: RF solution was kept in oven at 80 ° C for 30 minutes, then cardboard was immersed for 30 to 300 seconds;
• Row 3: RF solution was kept in oven at 80 ° C for 60 min, then cardboard was immersed for 30 to 300 sec.

The samples were kept in sealed containers for 1 day at 80 ° C and then dried at 80 ° C for 1 day. The finished samples were hard and dark brown.

In the 3 to 8th Scanning electron micrographs (SEM) of the samples are shown. The assignment is shown in the following Table 1: TABLE 1 FIG. line Immersion time 3 1 300 s 4 1 30 s 5 2 30 s 6 2 300 s 7 3 30 s 8th 3 300 s

9 shows an SEM image of the cardboard used before the coating.

The SEM shows in the figures that the airgel has particle sizes in the range of 2 μm and that the airgel, which rests directly on the cardboard, is smaller than 500 nm. Exception is the sample "Series 3, 300 s" ( 8th ) in which the particles on the cardboard are also about 2 μm in size. One recognizes a good adhesion of the airgel particles to the cardboard surface. The airgel has not penetrated into the cardboard even after 300 s immersion time.

In order not to influence the material properties of the honeycomb structure itself, it is important that the aerosol solution does not penetrate into the material constituting the honeycomb structure. The material, ie the honeycomb structure, should be coated on the surface. However, this should be done completely and with good adhesion.

As from the SEM images in the embodiment 2 ( 3 to 8th ), the airgel adheres to the surface of the cardboard. Cardboard is a material from which a honeycomb structure may consist according to the invention. By immersing the cardboard in the aerosol solution, the cardboard is not penetrated by the solution. It is merely coated, so that the material properties of the cardboard, so the carrier material, not even be changed but remain intact.

Embodiment 3

Aramid honeycomb structure with super-flexible silica airgel

1. Preparation of Aerogell Solution (Silca Solution):

The starting chemicals methyltrimethoxysiloxane (MTMS), methanol, H ₃ O ⁺ (for example, dilute HCl) and cetyltrimethylammonium chloride (CTAC) were used in a molar mass ratio of MTMS: methanol 35: 1, MTMS: H ₃ O ⁺ of 4: 1 and MTMS: cetyltrimethylammonium chloride (CTAC) was also prepared 4: 1 and 180 minutes with constant stirring at room temperature for hydrolysis, followed by the addition of ammonium hydroxide, through which the gelation was initiated. Typically, 12.2 g of MTMS was dissolved in 100.24 g of methanol in a test tube, after which 2.034 g of CTAC and 6.445 g of 0.0001 M HCl solution were added. The test tube was covered with aluminum foil, the solution was stirred for 3 hours. The condensation reaction was initiated by the addition of 12.533 g of NH ₄ OH (28-30%).

2. Filling the honeycomb structure:

After attaching a piece HexWeb ^® was respectively (Hexcel, Belgium) (C1-6,4-24; C1-3,2-29) set with a size of 3 × 3 cm in about 13 mL silica solution.

3. Gelation of the airgel in the honeycomb structure:

The filled with airgel solutions aramid honeycomb structures (HexWeb ^®) was filled into sealable containers made of polypropylene (PP) and gelled in an oven at 50 ° C for five days.

4. Washing the composite material:

After five days, the containers were opened for an additional 5 days for washing and solvent exchange. For this purpose, the solution standing over the aerogels was removed twice daily and replaced by ethanol. In this way, methanol, water and unreacted starting materials and all additives were removed from the gel body.

5. Drying of the composite material:

Subsequently, the gels were dried in an extraction plant in flow by means of supercritical CO ₂ at 90-100 bar.

6. Results

The honeycomb material is almost perfectly wet. A scanning electron micrograph of the super-flexible silica airgel-filled aramid honeycomb structure 12 , The good adhesion of the airgel on the substrate is clearly visible here. The average density of the composite was 0.037 g / cc and the thermal conductivity was 0.034 W / mK. The results of the compression test ( 13 ) show that the composite material has a significantly higher elastic modulus compared to pure materials. The compression test of super-flexible silica aerogels, aramid honeycomb structures and composite materials in the plane ( 13a ) and perpendicular to the plane ( 13b ) is in 13 shown. Table 2 below summarizes the results: TABLE 2 material Modulus of elasticity, MPa Aramid honeycomb structures 0.03-0.108 in the plane 5.2-25.5 perpendicular to the plane super-flexible silica airgel 0.0025 Composite material (aramid honeycomb filled with super-flexible silica airgel) 0.028-0.137 in the plane 6.5-21.3 perpendicular to the plane

Embodiment 4

Aramid honeycomb structure with semi-flexible silica airgel

1. Preparation of the Aerogell Solution:

The starting chemicals methyltrimethoxysiloxane (MTMS) and (3-glycidoxypropyl) -methyldiethoxysilane (GPTMS) were introduced in the molar mass ratio MTMS: GPTMS = 0.25. The ratio of MTMS: methanol was 30: 1, that of MTMS: H ₃ O ⁺ 30: 1 and that of MTMS: cetyltrimethylammonium chloride (CTAC) = 0.071. An appropriate solution was prepared and brought to hydrolysis for 180 minutes with constant stirring at room temperature, followed by the addition of diethylenetriamine (DETA) in the ratio MTMS: DETA = 0.125, through which the gelation was initiated.

For example, 14.64 g of MTMS and 6.36 g of GPTMS were dissolved in 103.32 g of methanol. This was followed by the addition of 2.43 g of CTAC and 58.11 g of HCl. In the sealed test tube, the solution was stirred for 3 hours. In the last step, 1.38 g of DETA was added to the solution.

2. Filling the honeycomb structure:

After attaching a piece HexWeb ^® was respectively (Hexcel, Belgium) (C1-6,4-24; C1-3,2-29) placed in a size of 3 × 3 cm in about 13 mL silica solution.

3. Gelation of the airgel in the honeycomb structure:

The solution-filled aramid honeycomb structures were filled into tightly sealed polypropylene (PP) containers and gelled in an oven at 50 ° C for three days.

4. Washing the composite material:

After five days, the containers were opened for an additional 5 days for washing and solvent exchange. To do so, the solution above the gels was removed twice a day and replaced with ethanol. In this way, methanol, water and unreacted starting materials and all additives were removed from the gel body.

5. Drying of the composite material:

Subsequently, the gels were dried in an extraction plant in the flow by means of supercritical CO ₂ .

6. Result:

The honeycomb structure is completely filled with silica airgel. The honeycomb material is wetted almost perfectly. 14 shows a scanning electron micrograph of semi-flexible silica airgel filled aramid honeycomb. The good adhesion of the semi-flexible airgel on the substrate is clearly visible. The average density of the composite was 0.092 g / cc and the thermal conductivity was 0.038 W / mK. The results of the compression test show ( 15 ), that the composite material, compared to pure materials, has a much higher elastic modulus. Compression test of semi-flexible silica aerogels, aramid honeycomb structures and composite materials in the plane ( 15a ) and perpendicular to the plane ( 15b ). The results are summarized in Table 3 below: TABLE 3 material Modulus of elasticity, MPa Aramid honeycomb structures 0.03-0.11 in the plane 5,2-25,5 perpendicular to the plane semi-flexible silica airgel 0.074 regardless of the level Composite material: (aramid honeycomb filled with semi-flexible silica airgel) 0.06-0.16 in the plane 67-20.2 perpendicular to the plane

Embodiment 5:

Honeycombs prepared according to Example 1 were subjected to thermal decomposition behavior by means of thermogravimetric analyzes coupled with infrared spectroscopy.

Thermogravimetric analysis (TGA), also known as thermogravimetry, is an analytical method or method of thermal analysis or thermoanalytics in which the mass change of a sample is measured as a function of temperature and time. The samples were heated in an oven in a temperature range of 26 ° C to 1000 ° C. The mass loss was determined. At the same time, an analysis by means of infrared spectroscopy was carried out on the gases formed during the heating.

10 shows the TGA curves of an aramid honeycomb without airgel (dashed line) and an aramid honeycomb coated with RF airgel (solid line) (prepared according to Embodiment 1).

The TGA curve of aramid honeycombs (coated with phenolic resin) without airgel showed in the measured temperature range of 26 to 1000 ° C, a mass loss of about 50%, where you could see 2 stages at 100 ° C and 450 ° C. Although aramid decomposes at 500-550 ° C ( KE Perepelkin, Fiber Chemistry 35 (4), 265-269, 2003 ), you can see from the TGA curve that the decomposition continues up to 1000 ° C. This may be due to the resin coating of the honeycomb. For airgel-coated aramid honeycombs, the mass loss was about 57%. One recognizes a slight descent in the range 100-400 ° C and a stage at 450 ° C.

IR spectra recorded during pyrolysis at the TGA showed the decomposition products that resulted. The mass loss initially corresponds to the amount of escaping CO ₂ and physically absorbed water (peaks at 2400 cm ^-1 , 3500 and 1800 cm ^-1 ). Table 4 shows the absorption bands of the infrared spectrum (IR absorption bands) and the assignment to the chemical groups resulting from the pyrolysis of the aramid honeycombs. Table 5 shows the IR absorption bands additionally occurring in the pyrolysis of aramid honeycombs filled with RF airgel. Table 4: Gang [cm ^-1 ] group 3900-3700 water 3500 -NH valence oscillation 2300, 695 CO ₂ 3000-2600 -CH valence vibration 1739 -C = O valence vibration 1700-1500 NH ₂ deformation vibration Table 5: Gang [cm ^-1 ] group 3015 CH ₂ stretching vibration 1081 CO stretching vibration 3619 OH valence vibration

Embodiment 6:

Cardboard honeycombs were coated analogously to Embodiment 1 with an RF airgel. The same thermogravimetric analyzes as in Embodiment 5 were carried out. In 11 the TGA curves of paper honeycombs without filling (dashed line) and paper honeycomb with airgel filling (solid line) are shown.

The TGA curve of paper honeycomb without airgel showed a mass loss of 83% in the measured temperature range of 26 ° C to 1000 ° C. This takes place in 2 stages at 100 ° C and 300-400 ° C instead. In airgel-filled paper honeycombs, the mass loss was 39.9%. One recognizes in the spectrum ( 12 ) a slight descent in the range 100-300 ° C and further one stage at 350-400 ° C.

IR spectra recorded during the pyrolysis of the TGA measurement show the decomposition products that have been formed. The mass loss at the beginning corresponds to CO ₂ and physically absorbed water (peaks in the IR spectrum at 2400 cm ^-1 and at 1800 cm ^-1 ) ( Wang Shurong et. al, front. Energy Power Eng. China 1 (4), 413-419, 2007 ). Between 300-400 ° C appear several peaks. Table 6 shows the signals (bands) in the IR spectrum of the paper honeycomb. Table 7 shows the signals additionally occurring in the airgel filled honeycomb. Table 6: Gang [cm ^-1 ] group 3900-3500 water 2175 CO 2300, 695 -CO ₂ valence vibration 1739 -C = O 1500-900 CC and CO Table 7: Gang [cm ^-1 ] group 3000 Aryl-H valence vibration of aromatic compounds 2175 C = C valence vibration of aromatic rings 1300 -OH stretching vibration

The results of Embodiments 5 and 6 show that less honeycomb material decomposes when coated with airgel.

It should be noted that the samples were cut for the measurements after filling with airgel, so that at the interfaces honeycomb material was released. These sites are thus unprotected and begin to decompose faster or earlier during pyrolysis.

Embodiment 7:

To determine the stability of airgel-filled carrier structures, an aramid honeycomb, as was also used in Example 1, was tested for bending strength in a 3-point bending test. Likewise, an aramid honeycomb filled with RF airgel and made in accordance with Example 1 was tested for its bending strength in a 3-point bending test.

The bending strength is a value for the bending stress in a component subjected to bending. As the flexural strength exceeded, the component in which it breaks fails. It thus describes the resistance of a workpiece, which is opposite to its deflection or its breakage. The beige strength is usually tested in a bending test. Often the 3-point bending test is used. In the 3-point bending test, the test sample is positioned on two supports and loaded in the middle with a test stamp.

In the 3-point bending test, the aramid honeycomb exhibited a flexural strength of 1.04 N / mm ² . The RF airgel-filled aramid honeycomb exhibited a flexural strength of 1.78 N / mm ² . The flexural strength of the filled aramid honeycomb is thus about 1.7 times greater than that of the unfilled aramid honeycomb.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011082087 A1 [0004]
• DE 102004046495 A1 [0007]
• DE 102013216965 [0018]

Cited non-patent literature

• KE Perepelkin, Fiber Chemistry 35 (4), 265-269, 2003 [0069]
• Wang Shurong et. al, front. Energy Power Eng. China 1 (4), 413-419, 2007 [0073]

Claims (13)

Core material ( 1 ) of a carrier material with macroscopic cavities, in which the cavities are filled with an airgel. Core material ( 1 ) according to claim 1, characterized in that the carrier material comprises an open-cell or open-cell foam or a honeycomb structure. Core material ( 1 ) according to claim 2, characterized in that the honeycomb structure comprises paper honeycomb, honeycomb cardboard, aluminum honeycomb, aramid honeycomb or polymer honeycomb. Core material ( 1 ) according to one of claims 1 to 3, characterized in that the carrier material is coated. Core material ( 1 ) according to one of claims 1 to 4, characterized in that it further comprises at least one layer of material. Core material ( 1 ) according to claim 5, characterized in that the material layer comprises a filter made of fleece or paper. Core material ( 1 ) according to one of claims 1 to 6, characterized in that it has a density in the range of 0.1 to 0.3 g / cm ³ and / or a thermal conductivity in the range of 0.04 to 0.06 W / mK. Sandwich structure ( 3 ) comprising a core material ( 1 ) according to one of claims 1 to 7, wherein the core material ( 1 ) between two cover layers ( 2a . 2 B ) is arranged. Sandwich structure ( 3 ) according to claim 8, characterized in that the two outer layers ( 2a . 2 B ) are the same or different. Sandwich structure ( 3 ) according to claim 9, comprising a supporting skin, an outer skin and a flame-retardant core arranged between the supporting skin and the outer skin, characterized in that the core is a core material ( 1 ) according to one of claims 1 to 7. Sandwich structure ( 3 ) according to one of claims 8 to 10, characterized in that the cover layers ( 2a . 2 B ) are selected from fiber-containing plastic or metal. Sandwich structure ( 3 ) according to claim 11, characterized in that the fiber-containing plastic is selected from CFK, GFK, NFK or AFK. Sandwich structure ( 3 ) according to claim 11, characterized in that the metal is selected from aluminum or titanium.

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