Polyester usually refers to a polymer compound obtained by polycondensation of a dibasic acid and a diol, and its basic chain links are connected by ester bonds. There are many varieties of polyester fibers, such as polyethylene terephthalate (PET) fiber, polybutylene terephthalate (PBT) fiber, and polypropylene terephthalate (polypropylene terephthalate) fiber. , PPT) fiber, etc., among which the polyethylene terephthalate content is more than 85%, and the molecular weight is generally controlled between 18,000 and 25,000
The research on polyester began in the 1930s and was invented by British Whinfield and Dickson. It was industrialized in the United Kingdom in 1949 and in the United States in 1953. It is a late-developed product among large varieties of synthetic fibers. But the speed of development is very fast.
The molecular weight of polyester is 18000-25000, and the degree of polymerization is 100-140. Macromolecules have a symmetrical chemical structure. Under suitable conditions, macromolecules are easy to form crystals and the fiber structure is compact. Polyester macromolecules contain benzene rings, which are basically rigid macromolecules, and at the same time contain aliphatic hydrocarbon chains, which give the molecules a certain flexibility. Except for the presence of two alcohol-terminated hydroxyl groups in the macromolecule, there are no other polar groups. The ester group content is high, and hydrolysis and thermal cracking will occur at high temperature. Polyester is melt-spun, its cross-section is round, the longitudinal direction is glass rod-like, it is straight and smooth, and its density is 1.38～1.40g/cm3.
China abbreviates fibers with a polyethylene terephthalate content of more than 85% as polyester, commonly known as "Xinliang". There are many foreign product names, such as "Dacron" in the United States, "Tetoron" in Japan, "Terlenka" in the United Kingdom, and "Lavsan" in the former Soviet Union. Wait.
2. Cationic dyeable polyester (CDP) fiber
By introducing acidic groups capable of binding cationic dyes into the PET molecular chain, modified polyester (CDP) that can be dyed with cationic dyes can be obtained. CDP was first developed by DuPont of the United States. At the end of the 20th century, its output accounted for 1/6 of the total output of PET fiber. Its typical varieties include Dacron T64 and Dacron T65. CDP not only has good dyeing performance, but also can be dyed in the same bath with natural fibers such as wool, which facilitates the simplification of the dyeing process of blended fabrics. If it is blended or interwoven with ordinary polyester, it can also produce different colors in the same bath, which greatly enriches the color of the fabric. Therefore, CDP has become a fast-growing variety in modified polyester. The preparation of CDP mainly uses copolymerization, graft copolymerization and other methods to add a third monomer or a fourth monomer, such as sodium dimethyl isophthalate sulfonate (SIPM), to the PET macromolecular chain. Since negatively charged sulfonic acid groups are added to the CDP molecular chain, the metal ions on the sulfonic acid groups will be exchanged with the cations in the dye when dyeing, so the dye ions are fixed on the CDP macromolecular chain. The salts generated by dyeing are continuously removed in the aqueous solution, and the reaction is continuously carried out, and finally the dyeing effect is achieved.
The production process of CDP is similar to that of PET, which is divided into continuous and intermittent. Because of the different sources of raw materials, it can be divided into DMT route and PTA route. Because CDP adds new groups to the macromolecular chain, it destroys the original structure of the fiber and reduces the melting point, glass transition temperature and crystallinity of the fiber. In the amorphous region, the intermolecular voids increase, which is conducive to the penetration of dye molecules into the fiber. The strength of CDP is lower than that of ordinary polyester, but it improves the anti-pilling performance of the fabric, makes the hand feel soft and full, and can make high-end wool-like products. Ordinary CDP dyeing still needs high temperature (120～140℃) and high pressure or under the condition of adding carrier, so as to have better dyeability. Therefore, when choosing dyes, it is necessary to pay attention to the selected dyes to have better thermal stability. sex.
3. Normal temperature and pressure dyeable polyester (ECDP) fiber
In the ordinary PET polymerization process, adding a small amount of the fourth monomer can produce the normal temperature and pressure dyeable polyester ECDP. This is mainly due to the introduction of polyethylene glycol flexible segments on the PET macromolecular chain, which makes the molecular structure of the fiber looser and the The acid group is combined, so it can be dyed under normal pressure boiling dyeing conditions. ECDP fiber feels softer than CDP and PET fiber and has better wearing performance. However, due to the lower bond energy of the fourth monomer polyethylene glycol segment, the thermal stability of ECDP fiber is reduced, and the strength loss of ECDP fiber is more than 30% at the ironing temperature of 180℃. Therefore, fabrics made of ECDP fiber need to be extra careful when finishing, washing and ironing.