How many innovative dyeing and finishing technologies of four natural dyes do you know?

Natural dyes have low color brightness, uneven hues, and deviations in washability and weather fastness. These problems are largely determined by the dye structure and coloring process technology. In order to solve these problems, the industry has developed coloring methods such as media coloring method, biological enzyme coloring method, ultrasonic and microwave coloring method, and fiber modification coloring method.

1 The application of medium coloring technology

Natural dyes have low affinity for fibers and poor dyeing fastness. To solve this problem, a commonly used method in production is to use mordants to improve the affinity between natural dyes and fibers, and at the same time, it can also control the hue of the dye. At present, in addition to using natural dyes and finishing mordants that were commonly used in the past——
In addition to potassium aluminum sulfate, potassium dichromate, ferrous sulfate and copper sulfate, a variety of new mordants and processes have been developed.

Samanta et al. conducted a detailed study on the effects of mordant types and methods on the coloring performance of different fiber materials, while Han Xiaojun et al. mainly used natural dyes for wool coloring. Comparative experimental results with or without mordant dyeing prove that the use of mordant alone or mixed can expand the hue and have an effect on the brightness, chroma, and dye uptake rate of natural dyes. However, the dyeing fastness of wool fiber is not ideal.

Lin Xijiao and others introduced rare earth-citric acid complexes as mordants. Due to the adsorption properties of rare earths, the dyeing fastness was significantly improved. Yang Rong and others used rare earths as mordants in natural dye silk coloring. The results of dyeing percentage and apparent color depth were satisfactory, and the levelness of the fabric was also improved. Zheng et al. also used rare earth chloride as a mordant to color pure linen fabrics with natural dyes. At present, the development of new, environmentally friendly mordants is also a new direction in natural dye coloring research.

2 enzymatic coloring method

Enzyme is a new, environmentally friendly bioactive textile and dyeing auxiliary. In modern fabric technology, biological enzymes are mainly used in the pre-treatment and finishing of natural fibers, the digestion of impurities and the post-finishing of fabrics to improve the appearance and feel of the finished product.

Tsatsaroni et al. used α-amylase and insulin to surface treat cotton and wool, and then used natural dyes for coloring. The experimental results showed that the enzyme treatment simultaneously improved the coloring performance of natural dyes and the anti-oxidation properties of wool. shrinkage performance. Sun Jie et al. used pepsin to pretreat silk fabrics and used natural madder dye for coloring. Under optimal process conditions, the color depth and dyeing fastness of the treated silk fabrics were significantly higher than those of untreated silk fabrics ( The dyeing fastness of silk fabrics dyed with natural dyes has reached level 4 or above).

In addition to natural fibers, the dye uptake rate of carmine red is greatly improved after polyacrylonitrile fiber is treated with nitrile hydratase. At present, regardless of whether natural dyes are used, the application of biological enzymes in coloring is a new direction and has been used in dyeing and finishing processes.

3 Ultrasonic and microwave-assisted coloring

Ultrasonic and microwave dyeing aids have the advantages of high efficiency, low energy consumption, and low dye utilization. They can disperse, stir, digest, and improve chemical reaction efficiency in liquid media. Vankar et al. applied ultrasonic coloring to the coloring of several natural dyes, which significantly enhanced the dyeability, coloring depth, and dyeing fastness of the dyed fabric (compared with traditional coloring methods).

Microwaves mainly achieve dyeing and finishing purposes through direct thermal effects on polar molecules such as water molecules. Recent studies have shown that using microwave radiation in the process of coloring cotton fabrics with gardenia yellow can greatly shorten the coloring time. At present, microwave and ultrasound are auxiliary means and have not yet become mainstream, and can only be used in combination with other methods.

The modified auxiliary effect of 4 fibers

At present, there are many innovations and innovations in the fiber modification dyeing and finishing process of natural dyes, which mainly include physical modification and chemical modification. Chemical modification mainly uses modifiers to treat fiber surfaces. For example, quaternary ammonium salt cationic modifiers treat cotton fibers, which can significantly improve the coloring performance and dyeing fastness of natural dyes on cotton fibers. In the same way, cationic modification of linen fabric also improves the dyeing performance of natural rhubarb dye.

Physical modification of fabrics is currently mainly carried out using technologies including magnetic sputtering and low-temperature plasma treatment, which are generally used in conjunction with chemical modification. For example, low-temperature plasma etching of polyester fibers and the demonstration of chitosan graftingBranch modification treatment can make plant-based natural dyes dyeable.

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