An in-situ grown foam-filled honeycomb material integrating structure and microwave absorption, its preparation method and application

Abstract

This invention belongs to the field of advanced composite materials technology, specifically relating to an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption, its preparation method, and its application. The preparation method includes the following steps: placing polyvinylidene fluoride (PVDF) composite material in a mold, covering PVDF granules with a high-temperature resistant film, hot-pressing, pressing after placement, and cooling to obtain a PVDF sheet; placing the sheet in a mold, placing the honeycomb layer on top of the sheet, allowing it to melt statically, and then pressing the honeycomb layer into the sheet to obtain a honeycomb composite material; placing the honeycomb composite material in a fixed-size mold in a supercritical foaming reactor, then injecting carbon dioxide fluid, controlling the pressure and temperature, and after heat and pressure holding, depressurizing, cooling, and shaping to obtain the foam-filled honeycomb material. The foam-filled honeycomb material obtained by this preparation method achieves in-situ growth, with fully filled honeycomb cells and a uniform and delicate foam morphology.

Description

Technical Field

[0001] This invention belongs to the field of advanced composite materials technology, specifically relating to an in-situ grown foam-filled honeycomb material with integrated structure and microwave absorption, its preparation method and application. Background Technology

[0002] Advanced composite materials are a class of composite materials with excellent performance and broad application prospects. By combining two or more different materials, the advantages of each material are fully utilized to create new materials with specific and advanced functions.

[0003] Honeycomb material is a composite material, commonly referred to as a honeycomb structure in the aerospace field. A honeycomb structure is a sandwich structure whose core layer consists of a series of hexagonal, quadrilateral, or other honeycomb-like cells, with thin panels / skins glued (or brazed) to both sides of the core layer. Honeycomb structures offer higher strength and stiffness than other forms of sandwich structures. In the aerospace industry, honeycomb sandwich structures are frequently used to manufacture various panels, wing surfaces, decks, canopies, floors, engine cowlings, exhaust nozzles, sound-absorbing panels, heat shields, and satellite shells. Furthermore, honeycomb radar-absorbing materials, as lightweight functional materials with excellent electromagnetic wave absorption properties, have been applied in aircraft structural stealth components, such as wing leading edges, doors, and radomes for radar stealth, effectively reducing the aircraft's radar cross-section while maintaining structural strength and lightweight characteristics.

[0004] However, while honeycomb materials possess good compressive strength in the thickness direction, their compressive strength in the planar direction is relatively weak, making it difficult to meet the requirements for use in harsh environments. Especially under pressure, the honeycomb structure is prone to crushing, leading to structural failure. Furthermore, during the machining of aramid paper honeycomb, due to weak rigid support and significant fiber anisotropy, phenomena such as honeycomb cell wall collapse, delamination, and tearing easily occur, resulting in low processing efficiency and difficulty in controlling processing quality.

[0005] Therefore, improving the compressive strength and processing performance of honeycomb materials has become an urgent problem to be solved. Existing methods for enhancing the mechanical strength of honeycomb mainly involve: impregnation reinforcement and reinforcing with rigid foam through honeycomb paper. For impregnation reinforcement, the resin impregnation method, which is widely used in the existing technology, can partially improve mechanical properties, but its limitations are reflected in the need for multi-stage impregnation-curing cycles, resulting in high energy consumption and long cycles. It can also cause pore blockage due to excessive resin penetration, which seriously affects the material's air permeability, electromagnetic wave transmission and other additional functions.

[0006] For the method of reinforcing honeycomb paper with rigid foam, which is suitable for rigid foam with high mechanical strength, the honeycomb is prone to curling and deformation during the pressing process, resulting in a decrease in reinforcement effect or even structural failure. Therefore, developing a honeycomb material modification technology that can achieve isotropic reinforcement and maintain processing adaptability has become an urgent need for lightweight design in aerospace, rail transportation and other fields.

[0007] Furthermore, regarding microwave absorption performance, current impregnated microwave-absorbing honeycomb materials have reached a bottleneck in performance improvement. Especially under the stringent lightweight requirements of the aerospace field, simply increasing the thickness of the absorbent wall to enhance absorption performance is insufficient. This method not only improves the overall quality of the honeycomb but also limits the full interaction between radar waves and the material because the effective thickness of the honeycomb layer for radar wave interaction is relatively thin, with most of the space still filled with air that lacks microwave absorption capabilities. Therefore, there is an urgent need for an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption, along with its preparation method, to address the problems and limitations of existing technologies. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for preparing an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption, comprising the following steps:

[0009] S1: Place the polyvinylidene fluoride composite material in a mold, cover the polyvinylidene fluoride granules with a high-temperature resistant film, hot press, place and press, and cool to obtain polyvinylidene fluoride sheet.

[0010] S2: Place the board obtained in S1 into the mold, place the honeycomb on top of the board, let it stand and melt at high temperature, then press the honeycomb into the board to obtain the honeycomb composite material.

[0011] S3: The honeycomb composite material obtained in S2 is placed in a fixed-size mold in a supercritical foaming reactor, and then carbon dioxide fluid is injected. The pressure and temperature are controlled. After heat preservation and pressure holding, the pressure is released and cooled to solidify, thus obtaining the foam-filled honeycomb material.

[0012] Furthermore, the temperature during the hot pressing process described in S1 is 200°C.

[0013] Furthermore, the internal cavity dimensions of the fixed-size mold described in S3 are 250mm × 250mm × 200mm.

[0014] Furthermore, the dimensions of the honeycomb described in S2 are consistent with those of the board material.

[0015] Furthermore, the pressure described in S3 is 13-20 MPa, the temperature is 120-140°C, and the holding time is 0.5-2 hours.

[0016] An in-situ grown foam-filled honeycomb material integrating structure and microwave absorption is provided. The in-situ grown foam-filled honeycomb material has a fully filled honeycomb structure with foam pores of 30-50 micrometers and a uniform and delicate foam morphology.

[0017] An application of an in-situ grown foam-filled honeycomb material integrating structure and wave absorption, wherein the in-situ grown foam-filled honeycomb material integrating structure and wave absorption is used in the preparation of stealth components for aircraft structures.

[0018] Beneficial effects

[0019] This invention involves in-situ growth of a honeycomb structure by pressing it into a polyvinylidene fluoride (PVDF) composite material. Using advanced supercritical foaming technology, a rigid functional composite foam material is filled inside the honeycomb cells, achieving a dual improvement in the structural function of the honeycomb material while maintaining its lightweight properties. The in-situ foam filling supports the honeycomb walls, reducing local buckling and improving the overall stiffness and strength of the material while maintaining its lightweight characteristics. The maximum compressive stress in the thickness direction can be increased by 310% (from 0.1 MPa to 0.31 MPa). Simultaneously, the maximum compressive stress in the planar directions (W and L) can be increased from 0.3 kPa to 65 kPa. The energy absorption characteristics of the foam significantly enhance the impact absorption capacity of the filled honeycomb structure in all directions, making it particularly suitable for protective structures. The sealed foam structure effectively isolates heat and sound transmission, making it suitable for noise reduction applications in buildings and vehicles requiring good insulation performance. These technological advantages make foam-filled honeycomb materials promising for applications in aerospace, military protection, transportation, construction, and the automotive industries.

[0020] This invention utilizes microwave-absorbing foam to fill a honeycomb pore structure, transforming the interaction between radar waves and the honeycomb from surface interaction to volume interaction. This not only provides more absorption space but also achieves ultra-high foaming ratio through supercritical foaming technology, significantly reducing the foam density. This method effectively converts surface absorption to volume absorption while maintaining the material's lightweight properties, significantly improving radar wave absorption performance. The in-situ foam filling technology also enhances the processability of the honeycomb material, enabling it to meet more complex structural design requirements while reducing production and design costs. Furthermore, the microwave-absorbing filler in this invention can use graphene or iron carbonyl in addition to carbon nanotubes; the preparation method is also applicable to other thermoplastic polymers (PP, PS, PA, PC, PMMA, TPU); and the foaming agent involved in this invention can also be nitrogen, ethanol, or butane. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0022] Figure 1 Here are schematic diagrams and scanning electron microscope images of the in-situ growth of aramid paper honeycomb foam obtained in Example 1 of this invention;

[0023] Figure 2 This is a scanning electron microscope image of the in-situ grown aramid paper honeycomb microwave absorbing foam obtained in Example 1 of the present invention.

[0024] Figure 3 This is a test diagram of the compressive strength of the foam-filled honeycomb material obtained in Example 1 of the present invention;

[0025] Figure 4 This is a waveform absorption performance diagram of the microwave-absorbing foam-filled honeycomb material obtained in Example 1 of the present invention. Detailed Implementation

[0026] The following will describe, in conjunction with Embodiments 1-2 of the present invention and the appendix... Figures 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a method for preparing an in-situ grown foam-filled honeycomb material with integrated structure and microwave absorption, comprising:

[0028] S1: Weigh the polyvinylidene fluoride (PVDF) composite material used for foaming, place it in a mold, cover the PVDF granules with a high-temperature resistant film (PI), and put it into a hot press; adjust the parameters of the hot press, and then let it stand for an appropriate time to ensure that the PVDF melts. After pressing and cooling, a PVDF sheet is obtained.

[0029] S2: Place the polyvinylidene fluoride sheet obtained in S1 into a mold, place a honeycomb paper of the same size as the polyvinylidene fluoride sheet on top of the sheet, and hot press it to ensure that the sheet melts. Then, use low pressure to repeatedly press the honeycomb material into the sheet. After cooling, a honeycomb composite material is obtained.

[0030] S3: The honeycomb composite material obtained in S2 is placed in a constrained mold in a supercritical foaming reactor, and then carbon dioxide fluid is injected. After controlling the parameters and maintaining the temperature and pressure, the pressure is released to atmospheric pressure by opening the pressure relief valve. Finally, the sample is cooled and shaped with an ice-water mixture to obtain in-situ grown foam-filled honeycomb material.

[0031] Example 1

[0032] S1: Select 8g of polyvinylidene fluoride granules and put them into the mold. Cover the surface with a high-temperature resistant PI film to ensure that the surface is regular. Then put it into a hot press and let it stand at 200℃ for 10 minutes to ensure that it melts. Use a pressure of 5MPa and vacuum it. After cooling, you will get a 2mm thick polyvinylidene fluoride sheet.

[0033] S2: Using the same mold as S1, the honeycomb is placed on top of the plate. After melting at 200℃ for 10 minutes, the honeycomb is slowly and repeatedly pressed into the plate under a pressure of 0.5MPa to obtain a honeycomb composite material; the honeycomb thickness is 15mm.

[0034] S3: Place the honeycomb composite material into a square stainless steel mold with an inner cavity size of 250mm×250mm×200mm, ensuring that the stainless steel mold is placed flat, and place the cut honeycomb composite material in it; inject carbon dioxide fluid, control the pressure at 16MPa and the temperature at 126℃, and keep it at the temperature and pressure for 0.5h. Then, open the pressure relief valve to release the pressure to normal pressure. Finally, use an ice-water mixture to cool and solidify the sample to obtain a foam-filled honeycomb material with an expansion ratio of 8 times.

[0035] Example 2

[0036] 50g of polyvinylidene fluoride granules were placed into the feed barrel of a twin-screw extruder, and 2.5g of carbon nanotube powder was added in batches. The temperature of the extruder feed section was set to 200℃, and the temperature of the melting section and extrusion section was set to 220℃. Multiple extrusion granulation was performed to ensure uniform mixing. After pelleting, polyvinylidene fluoride composite material granules containing 5% carbon nanotubes were obtained and collected for subsequent use.

[0037] S1: Select 8g of the above composite material granules and put them into the mold. Cover the surface with a high-temperature resistant PI film to ensure that the surface is regular. Then put it into a hot press and let it stand at 200℃ for 10 minutes to ensure that it melts. Use a pressure of 5MPa and perform vacuuming. After cooling, a 2mm thick polyvinylidene fluoride (5% carbon nanotube) composite board is obtained.

[0038] S2: Using the same mold as S1, the honeycomb is placed on top of the plate. After melting at 200℃ for 10 minutes, the honeycomb is slowly and repeatedly pressed into the plate at 0.5MPa to obtain the honeycomb composite material; the honeycomb thickness is 15mm.

[0039] S3: Place the honeycomb composite material into a square stainless steel mold with an inner cavity size of 250mm×250mm×200mm, ensuring that the stainless steel mold is placed flat, and place the cut honeycomb composite material in it; inject carbon dioxide fluid, control the pressure at 16MPa and the temperature at 127℃, and keep it at the temperature and pressure for 0.5h. Then, open the pressure relief valve to release the pressure to normal pressure. Finally, use an ice-water mixture to cool and solidify the sample to obtain a foam-filled honeycomb material with an expansion ratio of 8 times.

[0040] Combination Figure 1 A schematic diagram and scanning electron microscope (SEM) image of in-situ foam growth in aramid paper honeycomb can be obtained. This invention achieves complete filling of the aramid paper honeycomb cavity with fine foam through an in-situ foaming molding process. The foam and honeycomb wall interface are densely bonded without defects. The SEM image shows that the filled foam has a closed-cell structure with a pore size uniformly distributed in the 20-40 μm range. The high proportion of micron-sized closed cells provides stable mechanical support and multiple electromagnetic wave scattering paths for the material. Furthermore, after introducing microwave absorbing filler (… Figure 2 It can still maintain uniform filling characteristics.

[0041] from Figure 3 The compressive strength of the foam-filled honeycomb material can be determined. Figure 3 (a) shows the compressive stress diagram in the thickness direction. Foam filling increases the maximum compressive stress in the thickness direction of the honeycomb material by 310% (from 0.1 MPa to 0.31 MPa). Figure 3 (b) shows the pressure resistance diagrams in the W and L directions. The diagram demonstrates that the foam filling significantly enhances the planar pressure resistance of the honeycomb structure, increasing the maximum compressive stress by 2166% (0.3 kPa → 65 kPa). Combined with... Figure 4 The microwave absorption performance (5% wt CNT) of the microwave-absorbing foam-filled honeycomb material can be obtained. It achieves full absorption in the X-band (8-12GHz) with a thickness of 4mm and a maximum reflection loss of -28dB.

[0042] This invention provides a method for preparing an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption. This method enhances aramid paper honeycomb through in-situ growth and filling. Existing technologies employ embedding methods, but these damage the honeycomb and foam structure, hindering large-scale production. Furthermore, the foam prepared by this invention has uniform pore size (less than 50 μm), a feature unmatched by existing honeycomb foam products. The method is simple and environmentally friendly, significantly improving the mechanical properties of the honeycomb, particularly its compressive strength in the planar direction. Moreover, this method allows the introduction of electromagnetic functional materials into the foam component, achieving structural and functional integration of the honeycomb foam. Existing methods lack the ability to uniformly disperse conductive fillers, failing to achieve effective microwave absorption. The synergistic effect of the honeycomb and microwave-absorbing foam in this invention, applying supercritical fluid foaming technology to high-performance structural honeycombs, is unprecedented in existing technologies.

Claims

1. A method for preparing an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption, characterized in that, Includes the following steps: S1: Place the polyvinylidene fluoride composite material in a mold, cover the polyvinylidene fluoride granules with a high-temperature resistant film, hot press, place and press, and cool to obtain polyvinylidene fluoride sheet. S2: Place the plate obtained in S1 into the mold, place the honeycomb on top of the plate, let it stand and melt, and then press the honeycomb into the plate to obtain the honeycomb composite material. S3: The honeycomb composite material obtained in S2 is placed in a fixed-size mold in a supercritical foaming reactor, and then carbon dioxide fluid is injected. The pressure and temperature are controlled. After heat preservation and pressure holding, the pressure is released and the material is cooled and shaped to obtain foam-filled honeycomb material. The pressure is 13-20 MPa, the temperature is 120-140℃, and the heat preservation and pressure holding time is 0.5-2 h.

2. The method for preparing an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption according to claim 1, characterized in that, The temperature during the hot pressing process described in S1 is 200°C.

3. The method for preparing an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption according to claim 1, characterized in that, The internal cavity dimensions of the fixed-size mold described in S3 are 250mm × 250mm × 200mm.

4. The method for preparing an in-situ grown foam-filled honeycomb material integrating structure and microwave absorption according to claim 1, characterized in that, The dimensions of the honeycomb described in S2 are consistent with those of the board material.

5. A structure-wave-absorbing integrated in-situ grown foam-filled honeycomb material obtained by the preparation method according to any one of claims 1 to 4, characterized in that, The aforementioned structure-wave absorption integrated in-situ grown foam-filled honeycomb material has a fully filled honeycomb structure with a pore structure of 30-50 micrometers and a uniform and delicate foam morphology.

6. The application of the in-situ grown foam-filled honeycomb material integrating structure and microwave absorption as described in claim 5, characterized in that, The in-situ grown foam-filled honeycomb material, which integrates structure and wave absorption, is used in the fabrication of stealth components for aircraft structures.

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