The clothing fibers provided by nature to mankind include not only cotton, hemp and other plant fibers, but also animal fibers such as wool and silk. Wool is the animal fiber that people first used to spin and knit sweaters to keep out the cold. Wool fabrics more than 3000 years ago have been unearthed in Xinjiang, China.
The main component of plant fiber is cellulose, and the main component of animal fiber is protein fiber. Wool fabrics made of animal fibers have better thermal insulation performance than cotton and linen fabrics made of plant fibers. However, the washing method of wool fabrics is more complex and cumbersome than that of cotton and linen fabrics. Why?
The fine structure of wool can be seen by observing it under an electron microscope. The wool surface is not smooth, covered with flakes. The substances that make up these scales are mainly protein molecules. The protein molecules in the scales are spiral, which can be easily elongated after absorbing water, and will shrink back after drying. However, if it is pulled too long when it is wet, it will be permanently deformed and will not shrink back. When washing, if the temperature is too high, the alkalinity of soap water is too strong, and the kneading is too strong, the wool will change permanently, so it is best to dry clean the sweater.
In fact, dry cleaning is to dissolve the dirt on the sweater with chemical solvent and then remove it. The commonly used dry cleaning agents are tetrachloroethylene, perchloroethylene, etc. They are usually insoluble in water and have strong oil solubility. They can dissolve oil stains and other stains; Low boiling point, easy distillation, can be used repeatedly; High flash point or no flash point, not easy to burn; High surface tension makes it easier to separate stains from clothes.