Popular Science | Not all polyester fibers are called polyester

Polyester (polyester) usually refers to a polymer compound obtained by the condensation of dibasic acid and dihydric alcohol, with esters between the basic chains key connection. There are many types of polyester fibers, such as polyethylene terephthalate (PET) fiber, polybutylene terephthalate (PBT) fiber, polypropylene terephthalate (polypropylene terephthalate) , PPT) fibers, etc., among which fibers with a polyethylene terephthalate content of more than 85% are the main ones. The molecular weight is generally controlled between 18,000 and 25,000. The simplified main molecular structure is as follows:

Above: The molecular structure of polyester.

The research on polyester began in the 1930s and was invented by the British Whinfield and Dickson. It was realized in the UK in 1949 and in the United States in 1953. Industrialized production, it is a late-developing product among the large varieties of synthetic fibers, but it develops very quickly.

The molecular weight of polyester is 18,000 to 25,000, and the degree of polymerization is 100 to 140. Macromolecules have a symmetrical chemical structure. Under suitable conditions, macromolecules can easily form crystals and have a tight fiber structure. Polyester macromolecules contain benzene rings, which are basically rigid macromolecules, and also contain aliphatic hydrocarbon chains, which give the molecules a certain degree of flexibility. In addition to the presence of two terminal alcohol hydroxyl groups in the macromolecule,�, no other polar groups. It has a high ester group content and will undergo hydrolysis and thermal cracking at high temperatures. Polyester is melt-spun. Its cross-section is circular, its longitudinal direction is glass rod-shaped, straight and smooth, and its density is 1.38~1.40g/cm3.

China refers to fibers with a polyethylene terephthalate content of more than 85% as polyester, commonly known as “Qianliang”. 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.

Introducing binding cations into the PET molecular chain By removing the acidic groups of dyes, modified polyester (CDP) that can be dyed with cationic dyes can be produced. CDP was first developed by DuPont in the United States. At the end of the 20th century, its output accounted for 1/6 of the total PET fiber output. Its typical varieties include Dacron T64, Dacron T65, etc. CDP not only has good dyeing properties, but can also be dyed in the same bath with natural fibers such as wool, which simplifies the dyeing process of blended fabrics. If blended and interwoven with ordinary polyester, it can also produce a different-color effect in the same bath, greatly enriching the color of the fabric. Therefore, CDP has become a rapidly developing variety among modified polyester. The preparation of CDP mainly uses copolymerization, graft copolymerization and other methods to add a third monomer or a fourth monomer to the PET macromolecular chain, such as sodium dimethyl sulfonate isophthalate (SIPM). Since a negatively charged sulfonic acid group is added to the CDP molecular chain, the metal ions on the sulfonic acid group will exchange with the cations in the dye during dyeing, so the dye ions are fixed on the macromolecular chain of CDP. The salts generated by dyeing are continuously removed in the aqueous solution, and the reaction continues, eventually achieving the dyeing effect.

CDP production The process is similar to that of PET, and can be divided into continuous and intermittent. Due to different sources of raw materials, it can be divided into DMT route and PTA route. CDP adds new groups to the macromolecular chain, thus destroying the original structure of the fiber. The melting point, glass transition temperature and crystallinity of the fiber are reduced. In the amorphous zone, the inter-molecule gaps are increased, which is beneficial to the penetration of dye molecules into the fiber. However, the strength of CDP is lower than that of ordinary polyester, but the fabric is more resistant to fluffing. The pilling performance is improved, making the hand feel soft and plump, and can be used to make high-grade wool-like products. The dyeing of ordinary CDP still requires high temperature (120~140℃) or the condition of adding a carrier, so as to have better dyeability. Therefore, when choosing dyes, you must pay attention to the fact that the selected dyes must have good thermal stability

In the ordinary PET polymerization process, adding a small amount of the fourth monomer can produce ECDP, a dyeable polyester at normal temperature and pressure. This is mainly due to the introduction of polyethylene glycol flexible segments into the PET macromolecular chain, which makes the molecular structure of the fiber looser and increases the amorphous area, which is more conducive for cationic dyes to enter the interior of the fiber and interact with more sulfonates. Acid groups are combined, so it can be dyed under normal pressure boiling dyeing conditions. ECDP fiber feels softer and has better wearability than CDP and PET fibers. However, due to the lower bond energy of the fourth monomer polyethylene glycol segment, the thermal stability of the ECDP fiber is reduced. At the ironing temperature of 180°C, the strength loss of the ECDP fiber reaches more than 30%. Therefore, fabrics made of ECDP fibers require special attention during finishing, washing and ironing.

PTT fiber is the abbreviation of polypropylene terephthalate fiber. Some people abroad call PTT a large-scale fiber in the 21st century. Fiber, its trade name is “Corterra”

PTT, PET and PBT belong to the same polyester family and have similar properties. PTT fiber has the characteristics of both polyester and nylon. It is easy to wash and quick-dry like polyester, has good elastic recovery and wrinkle resistance, and has good stain resistance, sun resistance and hand feel. It has better dyeing performance than polyester and can be dyed under normal pressure. Under the same conditions, the dye’s penetration into PTT fiber is higher than that of PET, and the dyeing is uniform and the color fastness is good. Compared with nylon, PTT fiber also has better wear resistance and stretch recovery, and has the characteristics of high elasticity and good fluffiness, so it is more suitable for making carpets and other materials.

PBT fiber is polybutylene terephthalate fiber Abbreviation. PBT fiber is made from the polycondensation of dimethyl terephthalate (DMT) or terephthalic acid (TPA), the main raw material of polyester, and 1,4-butanediol. DMT and 1,4-butanediol are used to perform a polycondensation reaction at a high temperature and vacuum, using organic titanium or tin compounds and tetrabutyl titanate as catalysts, and then melt spinning to make PBT fibers. The polymerization, spinning, and post-processing processes and equipment of PBT fiber are basically the same as those of polyester.

PBT The fiber has the same characteristics as polyester, such as good strength, easy washing and quick drying, dimensional stability, and good shape retention. The most important thing is that the flexible part of its macromolecular chain is longer, so it has long elongation at break and good elasticity. The elasticity does not change much and the hand feel is soft. Another advantage of PBT fiber is that it has better dyeability than polyester. PBT fabric can be dyed with disperse dyes under normal pressure boiling dyeing conditions. In addition, PBT fiber has better dyeing effect. Anti-aging, chemical resistance and heat resistance. PBT fiber is widely used in engineering plastics, household appliance casings, and machine parts.

PEN fiber is the abbreviation of polyethylene naphthalate fiber. Like polyester, PEN fiber is a semi-crystalline thermoplastic polyester material. It was originally launched by the American KASA company. Its production process is through 2,6-dimethyl naphthalate (NDC) and ethylene glycol (EG). It is obtained by transesterification and then polycondensation; another method is to directly esterify 2,6-naphthalenedicarboxylic acid (NDCA) and ethylene glycol (EG), and then by polycondensation. If a small amount of compounds containing organic amines and organic phosphorus are added, the thermal stability of PEN can be improved.

PEN fiber The spinning process is similar to that of polyester, and its process flow is: slice drying → high-speed spinning → drafting. Since the glass transition temperature of PEN fiber is higher than that of polyester, the drafting process must be changed accordingly. Multi-pass drafting should be used and the drafting temperature should be increased to avoid affecting the quality of the fiber due to slow molecular orientation. Compared with conventional polyester, PEN fiber has better mechanical and thermal properties, such as high strength, high modulus, good tensile resistance, high rigidity; good heat resistance, stable dimensions, not easy to deform, and has better Flame retardant; good chemical resistance and hydrolysis resistance; UV resistance and aging resistance.

By changing the fiber cross-sectional shape, the gaps between single fibers are increased, and the specific surface area is increased And the capillary effect greatly improves the moisture conductivity and makes moisture conductive and dry polyester filament. This fiber fabric has excellent moisture conductivity and moisture diffusion properties. When paired with fibers with good hygroscopicity such as cotton fiber and a reasonable organizational structure, the effect is better. The clothing made is dry, cool and comfortable to wear, and is suitable for knitting sports. Clothing, woven shirts, summer clothing fabrics, polyester stockings, etc.

Du Pont has developed a four-dimensional Tefra-Channel polyester fiber has excellent wicking ability. It is a highly moisture-conducting fiber made of hydrophobic synthetic fibers. It can wick sweat from highly sweaty skin to the surface of the fabric for evaporation.But. Research shows that the moisture removal percentage after 30 minutes is 52% for cotton fibers and 95% for four-channel polyester fibers. This fiber is particularly effective when used in sportswear and military thin thermal underwear. It can keep the skin dry and comfortable, and has excellent thermal insulation and cold protection functions.

WELLKEY was developed to use liquid sweat as Object to achieve thorough sweat absorption and quick drying. WELLKEY is a polyester hollow fiber. From the surface of the fiber, there are many pores that penetrate into the hollow part. Liquid water can penetrate from the fiber surface into the hollow part. This fiber structure aims at the maximum water absorption speed and moisture content. During the spinning process, a special micropore-forming agent is blended and then dissolved to form this fiber structure. This fiber has excellent sweat-absorbing and quick-drying properties and is mainly used as fabric for petticoats, tights, sportswear, shirts, training clothes, jackets and other clothing. In addition, due to its water-absorbing and quick-drying properties and low drying cost, it is used in non-wearing applications. It also has broad application prospects in the fields of medicine and health.

Early three-dimensional crimped fiber was made by using two polymers with different shrinkage properties through composite spinning technology and a specific cooling forming process. After stretching, due to the shrinkage It is made by the method of forming natural curls due to differences. The current preparation process has been greatly developed, that is, the unique patented technology of eccentric spinneret design is used, combined with the asymmetric forming cooling system and the corresponding subsequent stretching and shaping process. The fiber produced has high curl, natural and permanent curl, and good warmth retention. Currently, three-dimensional curled hollow fibers with four holes, seven holes, and even nine holes are widely used in the fields of filling and thermal insulation fibers. /p>