Introduced the development history and discoloration mechanism of photochromic fabrics, detailed the production methods and domestic and foreign research progress of photochromic fabrics, briefly described the application prospects of photochromic fabrics, and pointed out the use of The development of photochromic fabrics using inorganic photochromic materials is a direction worthy of research.
The historical and mechanism of photochromic fabrics were introduced, as the production methods and research progress in photochromic fabrics. The application of photochromic fabrics was described. It was pointed out that inorganic photochromic materials using in photochromic fabrics should be reserched in the future.
Photochromic fabric is a fabric with photochromic function. It originally appeared to meet the needs of military operations and was intended to achieve military camouflage.
1 The discoloration mechanism of photochromic fabrics
Currently, photochromic fabrics use certain processing methods to attach organic photochromic compounds to the surface of the fabric or inside the fibers, making them Has photochromic function. Although the mechanism is complex, the main cause of photochromism is discoloration due to changes in molecular structure.
In view of the fact that most organic photochromic systems, their photochromism is based on the reaction of single molecules. We can discuss the color-changing process through the photochromic reaction formula and UV-visible light absorption spectrum chart.
Photochromism means that a compound A undergoes a specific chemical reaction to produce product B when irradiated by light with a wavelength of λ1, and its absorption spectrum changes significantly, and when irradiated by light of another wavelength of λ2 Or under the influence of heat, it returns to its original form. That is, substance A transforms into its isomer B under light induction and changes color. Species A and B have different absorption spectra and energy level structures. Usually illumination causes species A to absorb energy and convert into species B with higher energy. Generally, B can be converted into A spontaneously or under the illumination of another wavelength.
Photochromism is a reversible chemical reaction. If a substance changes color due to an irreversible reaction under the action of light, it belongs to the general photochemistry category and not to the photochromic category.
The principle of photochromic reaction can be qualitatively described in Figure 1. In Figure 1, λA and λB represent the maximum absorption wavelengths of compound A and compound B respectively. When compound A is irradiated with light of λA wavelength, compound A will undergo a certain reaction to form compound B. As shown in the ultraviolet-visible spectrum, the absorption of A will gradually weaken, while the absorption of B will gradually increase. This process is generally accompanied by a deepening of the color in appearance, and is generally called the photochromic process. In turn, when compound B is irradiated with light of λB wavelength, the opposite process will occur. This process is generally called a photochromic or photofading process.
2 Production method of photochromic fabric
Photochromic textiles with photochromic function can be produced by applying photochromic compounds to textiles. Currently, photochromic textiles The preparation methods are mainly the following four.
2.1 Pigment printing method
The pigment printing method is to mix photochromic dye powder into a binder such as resin liquid, and then use color paste to print on the fabric. After fixing and After washing, drying and other procedures, photochromic fabrics are obtained. This method is non-selective to fibers and fabrics and is applicable to both woven and knitted fabrics. Color-changing coatings used for printing processing should meet the requirements of soft hand feel, good washing resistance, and good rubbing fastness.
2.2 Dope coloring method
Dope coloring refers to a method of producing photochromic fibers by uniformly dispersing photochromic compounds in the spinning solution of various types of chemical fibers. According to the different spinning solutions, it can be divided into 2 categories.
(1) Melt spinning
The photochromic compound is melted and blended with polyester, polypropylene and other polymers, or the photochromic compound is dispersed in energy The color masterbatch is made into a resin carrier mixed with spinning polymer, and then mixed into polyester, polypropylene and other polymers for melt spinning to produce photochromic fiber.
(2) Solution spinning
It is similar to the conventional solution spinning method, but it is necessary to add dyes with reversible discoloration function and preventive dyes to the spinning solution. The transfer reagent, that is, the photochromic compound and the reagent to prevent its transfer are directly added to the spinning solution for spinning.
2.3 Graft polymerization method
The graft polymerization method mainly uses graft polymerization technology to make the fiber have color-changing properties. For example, the fiber or fabric is impregnated with a monomer containing spiropyran derivatives, and the monomer (usually styrene or vinyl acetate) is grafted within the fiber to give the fiber photochromic properties.
2.4 Ink printing method
This is an application method based on microcapsule technology. The so-called microcapsules are to put photochromic compounds together with other additives (solvents, light stabilizers, etc.) and wrap them with natural or synthetic polymers or microbial membranes through phase separation, interface reaction methods, physical methods, etc. Small balls of several microns to tens of microns to avoid the influence of high temperature and other impurities, and to strengthen contact with other additives. The color-changing microcapsules are then fixed on the surface of the fabric using ink printing to obtain a photochromic fabric.
3 Research Progress of Photochromic Fabrics
3.1 Foreign Research Progress
At present, the countries that are currently researching and developing photochromic fabrics mainly include Japan, the United States, The United Kingdom and South Korea, among others, Japan has the most mature research and has applied for many patents. The United States and other European and American countries have also made a lot of progress in the research of photochromic clothing. As early as the early 1970s, the United States applied photochromic compounds to clothing to achieve the purpose of military camouflage. The solar active thread sold by the American Solar Active Company appears white indoors when there is no ultraviolet radiation. When placed outdoors, the ultraviolet rays activate the photochromic compound, causing the thread to change to produce a specific color. When the thread is removed from ultraviolet light for about 1 to 1.5 minutes, it can return to white. Tong Cheng, Tong Lin and others in Australia have developed photochromic fabrics that change color quickly and are washable up to 1,000 times. Currently, photochromic clothing produced by Japan's Zhongbo and Toray are mainly sold in overseas markets, and have achieved good market effects.
3.2 Domestic Research Progress
The research on photochromic textiles in my country is relatively lagging behind. Tu Zanrun et al. synthesized a spirocyclic photochromic dye with good performance. The product is sensitive to color change, bright in color, water-resistant, acid and alkali resistant, and can be used for printing and finishing of various fiber fabrics. Jiang Huidi and others used green and environmentally friendly spirocyclic microcapsule color-changing dyes and low-temperature adhesives to prepare a printing paste that can be used for silk printing. Meng Jiben and others used spirocyclic photochromic compounds and additives such as Yuanming powder, xanthan gum, sorbitol and thickeners to make photochromic dyes, which are suitable for the production of various fiber fabrics, wool and clothing. Donghua University used a mixed melt spinning method to produce two photochromic polypropylene fibers with good photochromic ability. One fiber will change from white to blue after being irradiated by sunlight, and the other fiber will change from white to blue after irradiation. Then changed from yellow to green. Jiang Yingying used printing coating technology to treat spirozine photochromic compounds on fabrics to make them photochromic.
4 Application Prospects of Photochromic Fabrics
At present, the research on photochromic materials at home and abroad is mainly organic photochromic materials, and their color-changing mechanism still needs to be studied in depth. Organic photochromic materials have the characteristics of sensitive color change and bright color, but the fabric is prone to oxidation and deterioration, has poor fatigue resistance, and is also expensive. Moreover, most dyes have insufficient affinity for fibers and are difficult to process through conventional dyeing and printing processes, which limits the application and promotion of photochromic fabrics. Overcoming these shortcomings of organic photochromic materials should be the focus of next research. At the same time, it should also be noted that although inorganic photochromic materials change color slowly, they are not easily affected by the environment and have good light resistance and fatigue resistance. Therefore, the development of photochromic fabrics using inorganic photochromic substances is a direction worthy of research.
References
[1] Cai Honghua, Luo Zhongkuan. Development status of photochromic materials and their application prospects in construction [J]. Guangdong Building Materials, 2007 (7): 22 ? 23.
[2] Cao Hui, Du Haiyan, Sun Jiayue. Organic photochromic compounds and their applications [J]. Materials Herald, 2006 (5): 331 ? 334.
[3] Sun Binbin, Fu Zhengsheng, Chen Jie. Application of photochromic materials in the military field [J]. Journal of Shaanxi National Defense Industry Vocational and Technical College, 2007, 17(1): 38? 40.
[4] Feng Changgen, Wang Jianying. Research progress on the photochromic reaction mechanism of spirozine[J]. Organic Chemistry, 2006, 26(7): 1012? 1023.
[5] Shen Qingyue, Lu Chunhua, Xu Zhongzi. Research and application of photochromic materials [J]. Materials Herald, 2005, 19 (10): 31 ? 35.
[6] Yang Songjie, Tian He. Organic photochromic materials The latest research progress [J]. Journal of Chemical Engineering, 2003, 54 (4): 497 ? 507.
[7] Zhang Changrui. Organic photochromic materials [J]. Chemical Education, 2009 (4): 6? 7.
[8] Jiang Yingying. Preparation of photochromic compounds and their application in textiles[D]. Qingdao: Qingdao University, 2009.
[9] Zhou Xiuhui. Production technology of color-changing fabrics [J]. Industrial Textiles, 1999, 17(8): 1? 4.
[10] Ge Jingyuan, Yang Wenfang. Application of color-changing materials in textiles[ J]. Dyeing and Finishing Technology, 2007, 29 (10): 5? 9.
[11] Feng Sheyong, Gu Lixia. Photosensitive color-changing fiber materials [J]. Synthetic Fiber Industry, 1997, 20 (3) ：36 ? 40.
[12] Maslowski E.Fibers and Textiles from Janpan [J]. Tekstil & Teknik, 1988, 4(46): 22.
[13] Zhang Xiaoying, Deng Xinhua, Bian Dongcai, et al. Application and development of photochromic materials in textiles [A]. China Academy of Textile Sciences. Proceedings of the 7th Symposium on Functional Textiles and Nanotechnology Applications [C]. Hangzhou ：409 ? 412.
[14] Tong Cheng, Tong Lin, Rex Brady, et al. Photochromic Fabrics with Improved Durability and Photochromic Performance[J]. Fibers and Polymers, 2008, 9 (5): 521? 526.
[15] Tu Zanrun, Ren Hongtu. Synthesis of photosensitive color-changing microcapsules and their application in textiles [J]. Printing and Dyeing, 1999 (10): 5? 8.