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Citation: Su, Y.; Zhao, X.; Han, Y. Phase Change Microcapsule Composite Material with Intelligent Thermoregulation Function for Infrared Camouflage. Polymers 2023, 15,3055. https://doi.org/ 10.3390/polym15143055
引自：Su， Y.;赵 X.;Han， Y. 具有红外伪装智能温度调节功能的相变微胶囊复合材料。聚合物 2023， 15,3055。https://doi.org/ 10.3390/polym15143055

Academic Editors: Jiangtao Xu and Sihang Zhang
学术编辑：徐江涛、张思航

Received: 19 June 2023  收稿日期： 2023-06-19
Revised: 9 July 2023  修订日期：2023 年 7 月 9 日
Accepted: 14 July 2023  录用日期： 2023-07-14
Published: 15 July 2023  发布日期：2023 年 7 月 15 日

Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
版权所有：©作者 2023 年。被许可人 MDPI，瑞士巴塞尔。本文是根据知识共享署名 （CC BY） 许可证 （https:// creativecommons.org/licenses/by/ 4.0/） 的条款和条件分发的开放获取文章。

Keywords: phase change microcapsules; infrared camouflage; emissivity; intelligent temperature regulation; textile composites
关键词：相变微胶囊;红外伪装;发射;智能温度调节;纺织复合材料

Matter is generally divided into three phases: solid, liquid, and gas. The transition between different phase states of the same material is called phase transition [1]. The substance whose state can be changed is called phase change material (PCM). When the phase change occurs, there is a significant energy exchange between the material and the environment, which will be strongly coupled with the heat transfer, so that the material has a certain temperature control and heat release function [2,3]. With this capability of phase change materials, the temperature around the working source or materials can be adjusted and controlled to reduce the mismatch between energy supply and demand in time and speed [4]. Therefore, phase change materials are applied broadly in the field of energy storage and temperature regulation [5,6]. However, phase change materials have problems such as large volume changes, easy leakage, and low thermal conductivity. Microencapsulation of phase change materials is an advanced application method. Microcapsule phase change material (MPCM), also known as phase change microcapsule, is a new type of composite phase change material with core-shell structure. It is coated with a stable polymer film on the surface of solid-liquid phase change material particles.
物质通常分为三个相：固体、液体和气体。同一材料的不同相态之间的转变称为相变 [1]。状态可以改变的物质称为相变材料 （PCM）。当相变发生时，材料与环境之间存在显着的能量交换，这种交换将与传热强耦合，使材料具有一定的温度控制和热释放功能 [2,3]。借助相变材料的这种能力，可以调整和控制工作源或材料周围的温度，以减少能源供需在时间和速度上的不匹配 [4]。因此，相变材料在储能和温度调节领域得到了广泛的应用[5,6]。然而，相变材料存在体积变化大、易泄漏、导热系数低等问题。相变材料的微胶囊化是一种先进的应用方法。微胶囊相变材料（MPCM），又称相变微胶囊，是一种具有核壳结构的新型复合相变材料。它在固液相变材料颗粒表面涂有一层稳定的聚合物膜。

The shell structure of microcapsules can provide good protection for phase change core materials, improve the stability of phase change materials, prevent chemical reactions with the outside world and leakage during long-term cyclic use, and significantly increase the contact area with the matrix material to improve thermal conductivity, thereby improving the working performance of phase change materials [7-9]. When the external temperature changes, the core material in the microcapsule will undergo phase change. The phase change material absorbs or releases a large amount of heat, and the temperature of the microcapsule itself remains constant, to achieve the effect of intelligent temperature regulation [10-13]. Phase change microcapsules with temperature regulation ability are widely used in construction [14-18], solar energy [19], food industry [20], textile [21,22], and other fields
微胶囊的壳结构可以为相变核心材料提供良好的保护，提高相变材料的稳定性，防止与外界发生化学反应和长期循环使用时的泄漏，并显著增加与基体材料的接触面积，提高导热系数，从而提高相变材料的工作性能[7-9]。当外部温度发生变化时，微胶囊中的芯材会发生相变。相变材料吸收或释放大量热量，微胶囊本身的温度保持恒定，达到智能调温的效果[10-13]。具有温度调节能力的相变微胶囊广泛应用于建筑[14-18]、太阳能[19]、食品工业[20]、纺织[21,22]等领域

In the modern battlefield, the infrared radiation energy of general military targets is higher than the background, so it is easy to find out by using infrared detectors. According to Stefan Boltzmann’s Law (1) [23], the total infrared radiation energy of an object is directly proportional to the fourth power of its emissivity and absolute temperature. Therefore, the possibility of the target being discovered by the infrared detector can be reduced by reducing the emissivity and controlling the temperature, to achieve its camouflage effect in the infrared band. Therefore, infrared camouflage materials that protect military targets without changing the shape and structure of the target have attracted extensive attention in the national defense and military industry [24]. Various infrared camouflage materials developed around fibers and fiber products are called infrared camouflage textile materials. Infrared camouflage textile materials are soft, portable, and wearable. They are the main raw materials of infrared camouflage clothing, backpacks, camouflage nets and tents. They can provide guarantee for the survival of soldiers and weapons and equipment, and plays an extremely important role in the battlefield [25,26]. In terms of reducing infrared emissivity, it mainly includes developing new low emissivity fibers [27-30], modifying existing fibers [31-33] or coating low infrared emissivity coatings [34-36]. In terms of temperature control, in addition to thermal insulation and structural design [37-40], the temperature regulating textile [41-44] and infrared camouflage textile [45-47] are prepared by combining phase change microcapsules with textile, which can effectively reduce the infrared radiation energy of the target [48-50]. However, it is difficult to use phase change microcapsules for infrared camouflage alone. Its phase change temperature, latent heat of phase change, and thermal conductivity can hardly meet the requirements of thermal camouflage. Only by combining with other functional materials can infrared camouflage be better realized [51]. According to Kirchhoff’s law, opaque objects with high reflectivity generally have low emissivity. Metal is a typical low-emissivity material, which is generally used in the field of infrared camouflage in the form of coating. Among them, copper and aluminum have become the main force of metal fillers due to their low cost and easy availability, excellent performance, and wide application. In this paper, phase change microcapsules are finished on the fabric, and the temperature-regulated fabric is obtained by changing different parameters. On this basis, the infrared camouflage fabric was prepared by adding low emissivity materials. Then its temperature adjustment ability, infrared camouflage effect, and mechanism are analyzed systematically. Compared with the untreated fabric, the prepared textile has a certain degree of infrared camouflage ability, which can delay the speed of temperature rise and effectively reduce the infrared thermal radiation.
在现代战场中，一般军事目标的红外辐射能量高于背景，因此使用红外探测器很容易发现。根据斯特凡·玻尔兹曼定律 （1） [23]，物体的总红外辐射能量与其发射率和绝对温度的四次方成正比。因此，可以通过降低发射率和控制温度来降低目标被红外探测器发现的可能性，从而在红外波段达到其伪装效果。因此，在不改变目标形状和结构的情况下保护军事目标的红外伪装材料在国防和军工工业中引起了广泛关注 [24]。围绕纤维和纤维制品开发的各种红外伪装材料称为红外伪装纺织材料。红外迷彩纺织材料柔软、便携、耐磨。它们是红外迷彩服、背包、迷彩网和帐篷的主要原材料。它们可以为士兵的生存和武器装备提供保障，在战场上发挥着极其重要的作用[25,26]。在降低红外发射率方面，主要包括开发新的低发射率光纤[27-30]、改性现有光纤[31-33]或涂覆低红外发射率涂层[34-36]。在温度控制方面，除了保温和结构设计[37-40]外，通过将相变微胶囊与纺织品相结合，制备了调温纺织品[41-44]和红外迷彩纺织品[45-47]，可有效降低目标的红外辐射能量[48-50]。 然而，单独使用相变微胶囊进行红外伪装是困难的。它的相变温度、相变潜热和导热系数很难满足热伪装的要求。只有与其他功能材料结合，才能更好地实现红外伪装 [51]。根据基尔霍夫定律，具有高反射率的不透明物体通常具有低发射率。金属是一种典型的低辐射率材料，一般以涂层的形式用于红外伪装领域。其中，铜和铝因其成本低廉、易得、性能优良、应用广泛而成为金属填料的主力军。在本文中，在织物上完成相变微胶囊，并通过改变不同的参数获得温度调节织物。在此基础上，通过添加低发射率材料制备了红外迷彩织物。然后，系统分析了其温度调节能力、红外伪装效果和机理。与未经处理的织物相比，制备的织物具有一定的红外伪装能力，可以延缓升温的速度，有效减少红外热辐射。

where $E$$E$EE is the infrared radiation $\left(\mathrm{J}/(\mathrm{s}\cdot {\mathrm{m}}^2)\right),\sigma$$\left(\mathrm{J}/\left(\mathrm{s}\cdot {\mathrm{m}}^2\right)\right),\sigma$(J//(s*m^(2))),sigma\left(\mathrm{J} /\left(\mathrm{s} \cdot \mathrm{m}^{2}\right)\right), \sigma is Stefan Boltzmann constant, $\epsilon$$\epsilon$epsi\varepsilon is the emissivity of the target surface, and $T$$T$TT is the thermodynamic temperature of the target surface (K).
其中 $E$$E$EE 是红外辐射 $\left(\mathrm{J}/(\mathrm{s}\cdot {\mathrm{m}}^2)\right),\sigma$$\left(\mathrm{J}/\left(\mathrm{s}\cdot {\mathrm{m}}^2\right)\right),\sigma$(J//(s*m^(2))),sigma\left(\mathrm{J} /\left(\mathrm{s} \cdot \mathrm{m}^{2}\right)\right), \sigma 是斯特凡·玻尔兹曼常数， $\epsilon$$\epsilon$epsi\varepsilon 是目标表面的发射率， $T$$T$TT 是目标表面的热力学温度 （K）。

The fabric used in the experiment was cotton fabric, which was purchased from Hongfei Textile Manufacturing, Baoding, China. Phase change microcapsules are prepared
实验中使用的面料是棉织物，购自中国保定市鸿飞纺织制造有限公司。制备相变微胶囊
by in-situ polymerization with paraffin as core material and urea-formaldehyde resin as wall material. Urea and formaldehyde aqueous solutions were purchased from Meryer (Shanghai) Chemical Technology, Shanghai, China. Paraffin, OP emulsifier, triethanolamine, citric acid and petroleum ether were purchased from Beijing enokai Technology, Beijing, China. Polyurethane resin was purchased from Guangzhou Yuheng environmental protection materials, China. Hollow glass beads were purchased from Henan Bairun casting materials, Zhengzhou, China. Silicon dioxide was purchased from Jiangsu Tianxing’s new materials, Huaian, China. The copper powder was purchased from Nangong Xindun alloy welding material spraying, Xingtai, China. Aluminum powder was purchased from Shanghai Aladdin Biochemical Technology, Shanghai, China. All reagents were of analytical grade and used directly without further purification. The details are shown in Table 1.
以石蜡为芯材，脲醛树脂为壁材的原位聚合。尿素和甲醛水溶液购自中国上海的 Meryer （Shanghai） Chemical Technology。石蜡、OP 乳化剂、三乙醇胺、柠檬酸和石油醚购自中国北京 Enokai Technology。聚氨酯树脂购自中国广州禹衡环保材料有限公司。空心玻璃珠购自中国郑州的河南百润铸造材料公司。二氧化硅购自中国淮安的江苏天兴新材料公司。铜粉购自中国邢台市南工欣盾合金焊接材料喷涂有限公司。铝粉购自中国上海上海阿拉丁生化科技公司。所有试剂均为分析级试剂，无需进一步纯化即可直接使用。详细信息如表 1 所示。

Table 1. Material Information.
表 1.材料信息。

Mix urea and formaldehyde aqueous solution in a certain proportion, drop triethanolamine to adjust the pH value of the solution to be weakly alkaline, react at $70{}^{\circ }\mathrm{C}$$70{}^{\circ }\mathrm{C}$70^(@)C70{ }^{\circ} \mathrm{C} for 1 h , and add deionized water to form a stable urea/formaldehyde prepolymer solution. Add a certain amount of OP emulsifier and paraffin into deionized water, heat and melt, emulsify and disperse for $30\min (3000\mathrm{r}/\min )$$30\min (3000\mathrm{r}/\min )$30min(3000r//min)30 \mathrm{~min}(3000 \mathrm{r} / \mathrm{min}) at ${60}^{\circ }\mathrm{C}$${60}^{\circ }\mathrm{C}$60^(@)C60^{\circ} \mathrm{C}, and form a stable emulsion. Drop the prepolymer solution into the emulsion and stir for 20 min after dropping. Then slowly add citric acid solution, adjust the final pH value of the solution to be acidic, keep the temperature at ${60}^{\circ }\mathrm{C}$${60}^{\circ }\mathrm{C}$60^(@)C60^{\circ} \mathrm{C} for reaction for 1 h , and then raise the temperature to ${90}^{\circ }\mathrm{C}$${90}^{\circ }\mathrm{C}$90^(@)C90^{\circ} \mathrm{C}, and keep the temperature for reaction for 2 h . After the reaction, the microcapsule lotion was poured out, cooled, separated and filtered. The obtained microcapsules were washed twice with petroleum ether and deionized water, and dried to obtain white powder microcapsules.
将尿素和甲醛水溶液按一定比例混合，滴加三乙醇胺调节溶液的pH值呈弱碱性，反应 $70{}^{\circ }\mathrm{C}$$70{}^{\circ }\mathrm{C}$70^(@)C70{ }^{\circ} \mathrm{C} 1 h，加入去离子水，形成稳定的尿素/甲醛预聚物溶液。在去离子水中加入一定量的OP乳化剂和石蜡，加热熔融，乳化分散， $30\min (3000\mathrm{r}/\min )$$30\min (3000\mathrm{r}/\min )$30min(3000r//min)30 \mathrm{~min}(3000 \mathrm{r} / \mathrm{min}) ${60}^{\circ }\mathrm{C}$${60}^{\circ }\mathrm{C}$60^(@)C60^{\circ} \mathrm{C} 形成稳定的乳液。将预聚物溶液滴入乳液中，滴加后搅拌 20 分钟。然后缓慢加入柠檬酸溶液，将溶液的最终pH值调节为酸性，保持反应温度1 ${60}^{\circ }\mathrm{C}$${60}^{\circ }\mathrm{C}$60^(@)C60^{\circ} \mathrm{C} h，然后升温至 ${90}^{\circ }\mathrm{C}$${90}^{\circ }\mathrm{C}$90^(@)C90^{\circ} \mathrm{C} ，保持反应温度2 h。反应结束后，将微胶囊化妆水倒出，冷却，分离，过滤。所得微胶囊用石油醚和去离子水洗涤两次，干燥，得白色粉末微胶囊。
2.2.2. Preparation of Phase Change Microcapsule Temperature Regulating Textile by Dip Rolling
2.2.2. 浸轧制备相变微胶囊调温纺织品

Disperse the phase change microcapsule particles in water, add dispersant, adhesive, and penetrant, mix evenly to obtain the phase change microcapsule solution. The cotton fabric with $10\times 10{\mathrm{cm}}^2$$10\times 10{\mathrm{cm}}^2$10 xx10cm^(2)10 \times 10 \mathrm{~cm}^{2} was washed and dried. Put it into a beaker containing phase change microcapsule solution and fully wet it, with a bath ratio of 1:20. The phase change microcapsule fabric was obtained by two dipping and two rolling processes, drying at ${80}^{\circ }\mathrm{C}$${80}^{\circ }\mathrm{C}$80^(@)C80^{\circ} \mathrm{C} for 5 min , and then baking at ${120}^{\circ }\mathrm{C}$${120}^{\circ }\mathrm{C}$120^(@)C120^{\circ} \mathrm{C} for 2 min . Two groups of phase change microcapsule fabrics were prepared by changing the microcapsule content and adhesive content respectively.
将相变微胶囊颗粒分散在水中，加入分散剂、胶粘剂和渗透剂，混合均匀，得到相变微胶囊溶液。棉 $10\times 10{\mathrm{cm}}^2$$10\times 10{\mathrm{cm}}^2$10 xx10cm^(2)10 \times 10 \mathrm{~cm}^{2} 布经过洗涤和干燥。将其放入盛有相变微胶囊溶液的烧杯中，充分润湿，浴比为 1：20。相变微胶囊织物经两次浸渍和两次轧制工艺得到，干燥 ${80}^{\circ }\mathrm{C}$${80}^{\circ }\mathrm{C}$80^(@)C80^{\circ} \mathrm{C} 5 min，然后烘烤 ${120}^{\circ }\mathrm{C}$${120}^{\circ }\mathrm{C}$120^(@)C120^{\circ} \mathrm{C} 2 min。通过改变微胶囊含量和胶粘剂含量，制备了两组相变微胶囊织物。

Disperse the phase change microcapsule particles in water, add adhesive, thickener, dispersant and defoamer, and stir evenly to obtain phase change microcapsule coating.
将相变微胶囊颗粒分散在水中，加入胶粘剂、增稠剂、分散剂和消泡剂，搅拌均匀，得到相变微胶囊包衣。