What is the dyeing modification of polyester?

Polyester fiber is a hydrophobic synthetic fiber, lacking functional groups that can be combined with direct dyes, acid dyes, and basic dyes.

Although it has an ester group that can form hydrogen bonds with disperse dyes, polyester has a close molecular chain structure and it is difficult for dye molecules to enter the fiber, resulting in difficult dyeing and monotonous color, which directly affects the development of polyester fabrics. Due to the high crystallinity of polyester, there are only small voids in the fiber. When the temperature is low, the molecular thermal motion changes its position to a small extent. Under humid conditions, polyester fibers will not pass through as violently as cotton fibers. Swelling increases the voids, and it is difficult for dye molecules to penetrate into the fiber. Polyester can only be dyed with disperse dyes when dyeing, and it must be dyed under high temperature and high pressure or with the aid of a carrier. In order to improve the dyeing performance of polyester, considering the molecular structure, increasing the degree of looseness of molecular chains will help the entry of dye molecules. The main methods used to improve dyeing performance are: (1) Copolymerization with bulky compounds; (2) Blending spinning with compounds with plasticizing effect; (3) Introducing an ether bond and disperse dye affinity Harmony group. The polyester resin prepared by the copolymerization method has low melting point and low crystallinity, and the thermal and mechanical properties of the fiber are damaged to a certain extent.

Cationic dyes can be dyed and modified by copolymerizing polyester dyeing modifier, such as dimethyl phthalate-5-sodium sulfonate (commonly known as three monomers, English abbreviation SIPM) with polyester, and the copolymerized polyester molecular chain Introduced sulfonic acid groups, it can be dyed with cationic dyes. The dyed fabrics have bright colors and high dye exhaustion rate, which greatly reduces the discharge of printing and dyeing wastewater. The copolyester chips can also increase antistatic, anti-pilling and moisture absorption properties. It is one of the main methods to improve the dyeing performance of polyester in recent years. Japan Unijika Company uses 4 parts of cationic dyeable polyester containing sulfonic acid group isophthalate unit and 1 part of ethylene glycol/polyethylene glycol/sodium sulfonate isophthalate/p-benzene The block copolymer of dicarboxylic acid can be blended and spun to produce ultrafine fibers with high dyeing depth; before or during spinning, cationic active agent and a small amount of denaturing agent are added to copolymerize with BAET. After making it into a random linear polymer, its spinnability becomes better. This modified polyester can not only be dyed with cationic dyes, but also has anti-pilling properties and improved shrink recovery.

In addition, the cationic dyeable fiber was introduced at the same time. A modified polyester (PBT) that uses 1,4-butanediol instead of ethylene glycol as the second monomer has also joined the ranks of differentiated polyester. Substituting butanediol for ethylene glycol not only greatly increases the flexibility of the molecular chain, but also greatly improves the dyeing performance of the fiber, achieving normal pressure boiling dyeing. However, because the raw material price of 1,4-butanediol is much higher than that of ethylene glycol, PBT fiber lacks a competitive advantage in price. Therefore, at present, 1,4-butanediol is mainly added as the third monomer in conventional PET, which not only reduces the price of the fiber, but also improves its dyeing performance, and its thermal stability is much better than that of cationic dyeable fiber.

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