Transpiration-based imitated vegetation sodium polyacrylate / polyvinyl alcohol composite camouflage material and preparation method thereof

Abstract

The application belongs to the technical field of infrared camouflage materials, and particularly relates to a kind of imitated vegetation PAAS / PVA composite camouflage material based on transpiration and a preparation method thereof. The camouflage material is composed of a high-hygroscopic composite base material, a colorant, a metal pigment and a "bridging" material. The high-hygroscopic composite base material is composed of a hygroscopic inorganic substance and a hygroscopic polyacrylic acid sodium (PAAS) and polyvinyl alcohol (PVA) composite. The "bridging" material is a medium that plays a bridging role between colorants, between a colorant and a metal pigment, and between metal pigments. The composite camouflage material has low emissivity in the mid-infrared band, is highly regenerative and reversible, can be recycled and reused, has low preparation cost, high practicality and other characteristics, and can be used in the field of infrared camouflage for reducing the detectability of weapons and equipment.

Description

Technical Field

[0001] This invention belongs to the field of infrared camouflage materials technology, specifically relating to a vegetation-inspired sodium polyacrylate (PAAS) / polyvinyl alcohol (PVA) composite camouflage material based on transpiration and its preparation method. Background Technology

[0002] Infrared stealth technology refers to reducing or altering the infrared radiation characteristics of a target by effectively controlling its features, thereby achieving low detectability within a given environment. Since infrared detection targets are mostly weapons and equipment situated on cold surfaces with temperature differences of only tens of degrees Celsius, the difference in infrared radiation energy is relatively small. Therefore, reducing infrared emissivity has been the mainstream research focus in the past. However, with the improvement in the precision of infrared detection instruments, simultaneously reducing infrared emissivity and the temperature difference between the target and the background has become a key research focus.

[0003] Traditional camouflage materials reduce the infrared radiation characteristics of detected targets primarily by lowering infrared emissivity or reducing the temperature difference between the detected target and the background radiation environment. As described in Chinese patent CN106382854A, this invention uses radio frequency magnetron sputtering to prepare a visible-infrared compatible camouflage material, achieving a low emissivity in the mid-infrared band. This material consists of a substrate, an infrared low-emissivity layer, and an oxide thin film layer stacked together, with the emissivity layer and oxide thin film layer having a thickness of only 0.1–2 μm. With temperature changes, the expansion and contraction of each layer differs, and the thin film layers may detach due to uneven stress. As described in Chinese patent CN114705082A, this invention uses porous thermal insulation and phase change material thermal storage technology to prepare a 3D aerogel material with both infrared stealth and visible-light camouflage, achieving camouflage by reducing the temperature difference between the detected target and the background environment. According to the Stefan-Boltzmann law, at room temperature, controlling the target temperature is less effective than controlling infrared emissivity in infrared camouflage. As described in Chinese patent CN108485361A, this invention achieves low emissivity in the 8-14μm infrared band based on a graphene-containing infrared low emissivity coating. However, its aluminum powder content is too high, and its color is metallic grayish-white, which cannot meet the requirements of visible light camouflage, thus greatly limiting its application. Furthermore, it only reduces emissivity without considering the influence of temperature on infrared radiation, failing to achieve a combination of both.

[0004] Therefore, in order to achieve low detectability of infrared camouflage technology, developing infrared camouflage materials that simultaneously reduce infrared emissivity and decrease infrared radiation characteristics due to the temperature difference between the target and the ambient background is of great value and significance for the protection of weapons and equipment. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a vegetation-inspired PAAS / PVA composite camouflage material based on transpiration and its preparation method. The method first involves preparing a highly hygroscopic composite material that simulates transpiration, then combining it with colorants, metallic pigments, and a "bridging" material to form a casting solution. This solution is then used in a solution casting process to prepare the composite camouflage material. This material is the same color as plant leaves, has a lower infrared emissivity in the mid-infrared band than green plants, and simulates transpiration at a temperature similar to the vegetation background, thus achieving infrared camouflage performance.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows:

[0007] A vegetation-mimicking PAAS / PVA composite camouflage material based on transpiration comprises, by weight parts: 300-400 parts of a highly absorbent composite substrate, 1-5 parts of a bridging material, 10-30 parts of a hygroscopic inorganic material, 10-30 parts of a colorant, and 1-10 parts of a metallic pigment. The highly absorbent composite substrate is composed of sodium polyacrylate (PAAS) and polyvinyl alcohol (PVA), with PAAS accounting for 30-60% of the total mass of the highly absorbent composite substrate.

[0008] Furthermore, PAAS accounts for 50-60% of the mass of the highly hygroscopic composite substrate.

[0009] Furthermore, the molecular weight of the PAAS is 3 million to 7 million; the average molecular weight of the PVA is 110,000 to 130,000.

[0010] Furthermore, the bridging material has an electron mobility ≥15000 cm⁻¹. 2 The material with a strength of / (V·s) is preferably selected from any one or more of graphene, graphene oxide, and reduced graphene oxide.

[0011] The hygroscopic inorganic material is any one or more of highly hygroscopic inorganic materials such as lithium chloride and sodium chloride.

[0012] The pigment is any one or more of the following pigments that have a similar color to leaves: chrome green, phthalocyanine, chlorophyll and its derivatives.

[0013] The metallic pigment is any one or more of highly reflective materials such as aluminum powder, copper powder, and silver powder.

[0014] This invention also provides a method for preparing a vegetation-inspired PAAS / PVA composite camouflage material based on transpiration, comprising the following steps:

[0015] (1) Disperse PAAS uniformly in an ethanol solution to obtain a PAAS-ethanol mixed solution; dissolve the hygroscopic inorganic material in deionized water, add the pigment, and use ultrasonic vibration and stirring to uniformly disperse the pigment to obtain a suspension; add the PAAS-ethanol mixed solution to the suspension, heat the temperature to 70-80℃, and stir continuously at 300-500 rpm for 2-3 hours to obtain a PAAS casting solution.

[0016] (2) Disperse the bridging material evenly in an ethanol solution to obtain an ethanol solution of the bridging material; dissolve PVA in deionized water to obtain a PVA solution; add the ethanol solution of the bridging material to the PVA solution, heat to 90-95℃, rotate at 150-200 rpm, and stir continuously for 2-3 hours to obtain a PVA casting solution.

[0017] (3) Mix the PAAS casting solution and PVA casting solution evenly; add metallic pigments and stir for 1-2 hours; vacuum and let stand to remove bubbles; pour into a mold and dry at 60°C to obtain the vegetation-imitating PAAS / PVA composite camouflage material.

[0018] Furthermore, in step (1), the mass concentration of the PAAS-ethanol solution is 20wt% to 50wt%; the mass concentration of the pigment in the suspension is 0.1wt% to 1wt%. The PAAS solution has the characteristic of high viscosity. By uniformly dispersing the pigment in water beforehand and then adding the PAAS-ethanol solution, the stability of the pigment in the solution can be enhanced, ensuring uniform dispersion.

[0019] Furthermore, in step (2), the mass concentration of the bridging material in the ethanol solution is 0.1wt% to 1wt%; the concentration of the PVA solution is 1wt% to 20wt%. PVA forms a hydrogen bond network with the hydroxyl groups of the bridging material, making each layer of the bridging material form a dense molecular layer, which makes the bridging material less prone to agglomeration and more uniformly dispersed.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The present invention establishes a bridging effect between pigments, between pigments and metallic pigments, and between metallic pigments through bridging materials.

[0022] (2) This invention combines hygroscopic inorganic materials and hygroscopic substrate sodium polyacrylate (PAAS) with polyvinyl alcohol (PVA) to form a highly hygroscopic substrate; by adsorbing water vapor at night and desorbing moisture during the day, it simulates the transpiration of vegetation, thereby reducing the temperature difference between it and the vegetation background; by using specific pigments to achieve the same color and spectrum as plant leaves, it achieves optical camouflage; by using metallic pigments and bridging materials as low emissivity fillers, it reduces the infrared emissivity of the composite substrate; that is, it simultaneously reduces the surface temperature and infrared emissivity of the material, thereby making the infrared radiation characteristics of the target more similar to the vegetation background.

[0023] (3) This invention uses a combination of hygroscopic inorganic materials and hygroscopic polymers to adsorb moisture from the surrounding environment, allowing the moisture to evaporate continuously and achieving an evaporative cooling effect. High-reflectivity fillers such as metallic pigments reflect solar radiation or ambient high-temperature energy radiation, achieving a low-radiation cooling effect; that is, the combined use of traditional evaporative cooling and low-radiation cooling works together to reduce the temperature of the camouflage material.

[0024] (4) The vegetation-inspired PAAS / PVA composite camouflage material of the present invention has the characteristics of low emissivity, high regeneration and reversibility, recyclability and reusability, low preparation cost and strong practicality in the mid-infrared band, and can be used in the field of infrared camouflage to reduce the detectability of weapons and equipment. Attached image description:

[0025] Figure 1 A flowchart illustrating the preparation method of PAAS / PVA composite camouflage material;

[0026] Figure 2 The water vapor adsorption kinetic curves for Examples 1, 2, and 3 at different PAAS / PVA ratios under 20°C and 70% humidity are shown.

[0027] Figure 3 Examples 3, 4, and 5 show the water vapor adsorption kinetics curves at different LiCl contents under conditions of 20°C and 70% humidity.

[0028] Figure 4 This is an optical micrograph of Example 3 magnified 100 times;

[0029] Figure 5 Emissivity spectra of Examples 3, 6, 7, and 8 in the mid-infrared band;

[0030] Figure 6 Infrared camouflage thermal images of Examples 3, 6, 7, and 8 and green vegetation; Detailed Implementation

[0031] The present invention will be further described in conjunction with the embodiments and accompanying drawings:

[0032] The flowchart of the preparation method of vegetation-inspired PAAS / PVA composite camouflage material based on transpiration is shown below. Figure 1 .

[0033] Example 1

[0034] Weigh 112.5 parts of PAAS and premix and disperse them using anhydrous ethanol at a mass ratio of 1:2. Weigh 30 parts of anhydrous lithium chloride and 30 parts of chromium green, add them to 100 ml of deionized water, and mechanically stir for 10 min at a stirring speed of 150 rpm. Add the predispersed PAAS to the above lithium chloride / chromium green solution, increase the stirring speed to 360 rpm, set the heating temperature to 90℃, and continue stirring for two hours to obtain the PAAS casting solution. Weigh 2 parts of graphene oxide and premix and disperse them using anhydrous ethanol at a mass ratio of 1:200. Weigh 262.5 parts of PVA (making the mass ratio of PAAS to PVA 3:7), add them to 50 ml of deionized water, add the premixed and dispersed graphene oxide, set the heating temperature to 90℃, and stir at a stirring speed of 180 rpm for two hours to obtain the PVA casting solution.

[0035] Mix the PAAS casting solution and PVA casting solution, stir at room temperature for 0.5 hours, add 6 parts of floating aluminum powder, continue stirring for 2 hours, vacuum and let stand to remove bubbles; pour into a petri dish, place in a 60℃ constant temperature drying oven to dry, and you will get the PAAS / PVA composite camouflage material.

[0036] Example 2

[0037] Weigh 187.5 parts of PAAS and premix and disperse them using anhydrous ethanol at a mass ratio of 1:2. Weigh 30 parts of anhydrous calcium chloride and 30 parts of chromium green, add them to 100 ml of deionized water, and mechanically stir for 10 min at a stirring speed of 150 rpm. Add the pre-dispersed PAAS to the above calcium chloride / chromium green solution, increase the stirring speed to 360 rpm, set the heating temperature to 90℃, and continue stirring for two hours to obtain the PAAS casting solution. Weigh 2 parts of graphene oxide and premix and disperse them using anhydrous ethanol at a mass ratio of 1:200. Weigh 187.5 parts of PVA (making the mass ratio of PAAS to PVA 5:5), add them to 50 ml of deionized water, add the premixed and dispersed graphene oxide, set the heating temperature to 90℃, and stir at a stirring speed of 180 rpm for two hours to obtain the PVA casting solution.

[0038] Mix the PAAS casting solution and PVA casting solution, stir at room temperature for 0.5 hours, add 6 parts of floating aluminum powder, continue stirring for 2 hours, vacuum and let stand to remove bubbles; pour into a petri dish, place in a 60℃ constant temperature drying oven to dry, and you will get the PAAS / PVA composite camouflage material.

[0039] Example 3

[0040] Weigh 225 parts of PAAS and premix and disperse them using anhydrous ethanol at a mass ratio of 1:2. Weigh 30 parts of anhydrous lithium chloride and 30 parts of chromium green, add them to 100 ml of deionized water, and mechanically stir for 10 min at a stirring speed of 150 rpm. Add the predispersed PAAS to the above lithium chloride / chromium green solution, increase the stirring speed to 360 rpm, set the heating temperature to 90℃, and continue stirring for two hours to obtain the PAAS casting solution. Weigh 2 parts of graphene oxide and premix and disperse them using anhydrous ethanol at a mass ratio of 1:200. Weigh 150 parts of PVA (making the mass ratio of PAAS to PVA 6:4), add them to 50 ml of deionized water, add the premixed and dispersed graphene oxide, set the heating temperature to 90℃, the stirring speed to 180 rpm, and continue stirring for two hours to obtain the PVA casting solution.

[0041] Mix the PAAS casting solution and PVA casting solution, stir at room temperature for 0.5 hours, add 6 parts of floating aluminum powder, continue stirring for 2 hours, vacuum and let stand to remove bubbles; pour into a petri dish, place in a 60℃ constant temperature drying oven to dry, and you will get the PAAS / PVA composite camouflage material.

[0042] Example 4

[0043] The difference between this embodiment and Embodiment 3 is that the amount of anhydrous lithium chloride used is 15 parts.

[0044] Example 5

[0045] The difference between this embodiment and Embodiment 3 is that anhydrous lithium chloride is not used.

[0046] Example 6

[0047] The difference between this embodiment and Embodiment 3 is that graphene oxide and aluminum powder are not used.

[0048] Example 7

[0049] The difference between this embodiment and Embodiment 3 is that chrome green and aluminum powder are not used.

[0050] Example 8

[0051] The difference between this embodiment and Embodiment 3 is that chrome green and graphene oxide are not used.

[0052] The performance of the composite materials prepared in Examples 1-8 was tested, and the results are as follows:

[0053] Figure 2 The images show the water vapor adsorption kinetics curves for Examples 1, 2, and 3 at 20°C and 70% humidity, with different PAAS / PVA ratios. From... Figure 2It can be seen that as the proportion of sodium polyacrylate in the hygroscopic substrate increases, the hygroscopic performance improves and the adsorption capacity gradually increases. More moisture can be used for evaporation and heat absorption in low humidity environments, thus better simulating the transpiration cooling effect of vegetation.

[0054] Figure 3 The images show the water vapor adsorption kinetics curves for Examples 3, 4, and 5 at 20°C and 70% humidity under different lithium chloride contents. From... Figure 3 It can be seen that as the proportion of lithium chloride in the hygroscopic substrate increases, the hygroscopic performance improves and the adsorption capacity gradually increases. More moisture can be used for evaporation and heat absorption in low humidity environments, thus better simulating the transpiration cooling effect of vegetation.

[0055] Figure 4 This is an optical micrograph of Example 3 magnified 100 times. (From...) Figure 4 It can be seen that each component is uniformly dispersed in the casting solution.

[0056] Figure 5 The emissivity spectra of Examples 3, 6, 7, and 8 are shown in the mid-infrared band. It can be seen that the emissivity of the transpiration-based vegetation-mimicking PAAS / PVA composite camouflage material of the present invention is approximately 0.86, lower than the infrared emissivity of normal vegetation (0.94).

[0057] Figure 6 To illustrate how the transpiration-based vegetation-inspired PAAS / PVA composite camouflage materials prepared in Examples 3, 6, 7, and 8 were placed in an outdoor green plant environment, infrared camouflage thermal images of the average environmental radiation temperature of the vegetation and the radiation temperature of the camouflage material at a certain moment are obtained.

Claims

1. A transpiration-based, vegetation-imitating, sodium polyacrylate / polyvinyl alcohol composite infrared camouflage material, characterized by, By mass fraction, it comprises: 300-400 parts of high-hygroscopic composite base material, 1-5 parts of bridging material, 10-30 parts of hygroscopic inorganic substance, 10-30 parts of colorant, and 1-10 parts of metal pigment; the high-hygroscopic composite base material is composed of sodium polyacrylate and polyvinyl alcohol, wherein the mass percentage of sodium polyacrylate in the high-hygroscopic composite base material is 40-60%; the bridging material is graphene oxide; the hygroscopic inorganic substance is any one or several of lithium chloride and calcium chloride; the colorant is chromium green; and the metal pigment is aluminum powder.

2. The transpiration-based, simulated-vegetation, sodium polyacrylate / polyvinyl alcohol composite, infrared camouflage material according to claim 1, characterized in that, The molecular weight of the sodium polyacrylate is 3-7 million; and the average molecular weight of the polyvinyl alcohol is 110,000-130,000.

3. A method for preparing a transpiration-based, vegetation-mimicking, sodium polyacrylate / polyvinyl alcohol composite infrared camouflage material according to claim 1, characterized in that, It comprises the following steps: (1) uniformly dispersing sodium polyacrylate in an ethanol solution to obtain a sodium polyacrylate-ethanol mixed solution; dissolving a hygroscopic inorganic substance in deionized water, adding a colorant, and uniformly dispersing the colorant by ultrasonic oscillation and stirring to obtain a suspension; adding the sodium polyacrylate-ethanol mixed solution to the suspension, heating at a temperature of 70-80℃, and continuously stirring at a speed of 300-500 rpm for 2-3 hours to obtain a sodium polyacrylate casting solution; (2) uniformly dispersing a bridging material in an ethanol solution to obtain a bridging material ethanol solution; dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution; adding the bridging material ethanol solution to the polyvinyl alcohol solution, heating at a temperature of 90-95℃, and continuously stirring at a speed of 150-200 rpm for 2-3 hours to obtain a polyvinyl alcohol casting solution; (3) uniformly mixing the sodium polyacrylate casting solution and the polyvinyl alcohol casting solution; adding a metal pigment, stirring for 1-2 hours; vacuumizing and standing to remove bubbles; pouring into a mold, and drying at 60℃ to obtain an imitation vegetation sodium polyacrylate / polyvinyl alcohol composite infrared camouflage material.

4. The method for preparing transpiration-based, vegetation-simulating, sodium polyacrylate / polyvinyl alcohol composite infrared camouflage material according to claim 3, characterized in that, In step (1), the mass concentration of the sodium polyacrylate-ethanol solution is 20wt%-50wt%; and the mass concentration of the colorant in the suspension is 0.1wt%-1wt%.

5. The method for preparing transpiration-based, imitated vegetation, sodium polyacrylate / polyvinyl alcohol composite infrared camouflage material according to claim 3, characterized in that, In step (2), the mass concentration of the bridging material in the bridging material ethanol solution is 0.1wt%-1wt%; and the concentration of the polyvinyl alcohol solution is 1wt%-20wt%.

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