Photochromic fiber materials and thermochromic fiber materials for photochromic clothing

In the world of colorful colors, there are all kinds of different colors, which make our visual feeling not monotonous, but also affect our mood. Red makes us feel warm, passionate, joyful, dangerous and bloody. Green brings vitality, nature and peace. Blue makes us feel expansive and melancholy. While everything has its own color and does not change, there are a few plants and animals that change color in nature. Photosensitive clothes will bring you a different visual feast, the following take you to understand the photosensitive clothes.

Photochromic materials are divided into organic and inorganic types. The organic class has spiropyran derivative, azobenzene derivative and so on. This kind of color changing material has the advantages of light emission color and achromatic block, but it has poor thermal stability and oxidation resistance, low fatigue resistance, and is greatly affected by the environment. Inorganic doped single crystal SrTiO3 can photochromic, which overcomes the shortcomings of organic photochromic materials, such as poor thermal stability, low oxygen resistance and low fatigue resistance, and is not affected by the environment. However, the inorganic photochromic material develops color and desaturation slowly and has larger particle size. Photochromic fiber is made by blending photochromic material and polymer through solution spinning, blending spinning or composite spinning technology.

Photochromic fibers are fibers whose color changes when exposed to sunlight or ultraviolet light, and then reversibly change back to the original color when the light disappears. Since the discovery in 1899 that some solid and liquid compounds have photosensitive properties, the study of various photosensitive materials has aroused great interest. Japan first developed photochromic composite fiber, and on this basis made a variety of photosensitive fiber products, such as embroidered velvet, knitting yarn, woven yarn, etc., used for decorative leather, sports shoes, sweaters, etc., widely loved by people.

There are many examples of photochromic fiber materials. For example, after dyeing and finishing the acrylic fabric with cationic dye with chromic molecules, it changes color under different light sources, so it is called chromic knitted fabric. Levelling agent and acid have certain influence on the discoloration effect. The results show that the best color changing effect is obtained by using 1227 levelling agent and glacial acetic acid. The dyed acrylic knitted fabric must be opened before drying, and the drying temperature should be between 98℃ and 100℃. The fibers and fabrics prepared by this method have different tones at different wavelengths of light, which are all photochromic fiber fabrics. In addition, a Japanese company wrapped the spirofuran photosensitive material, which has changed from colorless to light blue or dark blue after absorbing the ultraviolet light of 350nm ~ 400nm wavelength, in the microcapsule to make photosensitive and discolored fabrics by printing process. Microencapsulation can improve the antioxidant capacity of photosensitizer, thus prolonging its service life. The photosensitive color changing T-shirt produced by this technology has been on the market since 1989, and similar products have been sold in China in recent years.

Thermochromic fibers are fibers whose color changes with temperature. In addition to filling thermochromic agent into the fiber, vinyl chloride polymer solution containing thermochromic microcapsules can also be coated on the fiber surface, and the solution can be gelled after heat treatment to obtain reversible thermochromic effect.

In the hot sun the clothes if it is pure white color, can reflect heat very well, so you won’t feel very hot, if enter indoor, it will become a light blue, give a person a kind of simple quietly elegant temperament, to in the evening, it will become beautiful purple, in the case of complete darkness and emits light faint light, this kind of clothes is quite attractive. In the sunlight or UV irradiation, the fibers that show different colors are called photosensitive fibers, and those that emit light after absorbing light are called light-storage fibers. Photochromic (also known as photosensitive or photosensitive) materials were first used in discolor-changing sunglasses. These discolor-changing materials absorb the energy of sunlight or ultraviolet rays, causing a color change and returning to the original color when the sunlight or ultraviolet rays are lost. The main chemical reactions are cis – trans isomerization, tautomerization, loop – opening and loop – closing reactions, sometimes dimerization or REDOX reactions.

The processing method of photochromic textile is similar to that of thermochromic textile. Microencapsulation can improve the antioxidant ability of photosensitizer, thus prolongs the service life of photosensitizer. The photosensitive compounds of furans, which change from colorless to light blue or dark blue after absorbing ultraviolet light at 350~400nm wavelength, are wrapped in microcapsules, which are used in printing technology to make photosensitive and color changing fabrics. Photosensitive color – changing T-shirts produced by this technology have been on the market since 1989. Nike has also used color-changing fibers on the LACES of its sneakers. The research on photosensitive fiber is just beginning in mainland China and has not yet entered the practical stage. At present, the photosensitive fiber is mainly used in entertainment clothing, safety clothing and decorations.

Before introducing the principle of light-storage (noctilucent) fiber, the reaction of absorbing light by organic compounds is introduced first. After absorbing light, electrons will be excited to the excited state. At this time, the absorbed energy must be released, which can be divided into photochemical reaction, emission, discharge and exothermic according to the different release ways.

Photochemistry results in structural changes such as cis-trans isomerization, addition, and cyclization. If there is a suitable medium to remove the electrons, and add compound (dye) electrons, the solar cell.

There are two different ways to emit light after absorption, electrons excited to the singlet state immediately emit light, the light put is called fluorescence, when the light source removed, immediately stop emitting light, generally used in the road lane separation line. If the singlet electron is converted to the triplet state by the internal system, the orbital transition of the electron is not allowed, but the light will be slowly released. This light is called phosphorescence. Even if the light source is removed, the compound will continue to emit light. Exothermic compounds, which vibrate or rotate molecules to release energy, are commonly used in sunscreens. Noctilucent fiber is the use of phosphorescent characteristics, in the absence of light, will still emit light, but the brightness of the lower, must be in the case of all black to see, and the light time is also limited, although the long-effect type light storage materials can reach more than 10 hours, but the brightness will decrease due to time. Light storage fibers can be used in furniture, curtains, escape signs and entertainment decorations.