Polyester usually refers to a high molecular compound obtained by polycondensation of dibasic acid and dibasic alcohol, and its basic chain links are connected by ester bonds. There are many kinds of polyester fibers, such as polyethylene terephthalate (PET) fiber, polybutylene terephthalate (PBT) fiber, polypropylene terephthalate (PPT) fiber, etc. among them, the fibers with polyethylene terephthalate content of more than 85% are the main ones, and the molecular weight is generally controlled between 18000 and 25000. The main molecular structure is as follows:
1. Polyester (PET) fiber
The research of polyester began in the 1930s. It was invented by British people such as whinfield and Dickson. In 1949, it was industrialized in Britain and in 1953 in the United States. It is a product of large varieties of synthetic fibers that developed late, but developed rapidly.
The molecular weight of polyester is 18000 ~ 25000, and the degree of polymerization is 100 ~ 140. Macromolecules have 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. At the same time, they also contain aliphatic hydrocarbon chains, making the molecules flexible. There are no other polar groups in the macromolecule except two alcohol terminated hydroxyl groups. With high ester content, hydrolysis and thermal cracking will occur at high temperature. Polyester is melt spun. Its cross section is round, its longitudinal direction is glass rod, and its density is 1.38 ~ 1.40g/cm3.
In China, the fiber with polyethylene terephthalate content greater than 85% is referred to as polyester, commonly known as “Dacron”. There are many foreign commodity names, such as “Dacron” in the United States, “tetoron” in Japan, “terlenka” in the United Kingdom, and “lavsan” in the former Soviet Union.
2. Cationic dyeable polyester (CDP) fiber
Modified polyester (CDP) can be dyed with cationic dyes by introducing acidic groups that can bind cationic dyes into PET molecular chains. CDP was first developed by American DuPont company. 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, dacron T65, etc. CDP not only has good dyeing performance, but also can be dyed in the same bath with natural fibers such as wool, which is convenient for simplifying the dyeing process of blended fabrics. If it is blended and interwoven with ordinary polyester, it can also produce the same bath different color effect, which greatly enriches the color of fabrics. Therefore, CDP has become a rapidly developing variety of modified polyester. CDP is mainly prepared by adding the third or fourth monomer, such as sodium dimethyl isophthalate sulfonate (SIPM), to the pet macromolecular chain by copolymerization and graft copolymerization. As a negatively charged sulfonic acid group is added to the CDP molecular chain, when dyeing, the metal ions on the sulfonic acid group will exchange with the cations in the dye, so the dye ions will be fixed on the CDP macromolecular chain. The salts generated by dyeing will be continuously removed in the aqueous solution, and the reaction will continue. Finally, the dyeing effect will be achieved.
The production process of CDP is similar to that of pet, which can be divided into continuous and intermittent. Due to different sources of raw materials, CDP can be divided into DMT route and PTA route. CDP destroys the original structure of the fiber due to the addition of new groups in the macromolecular chain, which reduces the melting point, glass transition temperature and crystallinity of the fiber. In the amorphous region, the intermolecular space increases, which is conducive to dye molecules penetrating into the fiber. The strength of CDP is lower than that of ordinary polyester, but the anti pilling property of the fabric is improved, and the handle is soft and plump. It can be used to make high-grade wool like products. The dyeing of common CDP still needs high temperature (120 ~ 140 ℃) and high pressure or under the condition of adding carrier, so as to have better dyeing property. Therefore, when selecting dyes, it must be noted that the selected dyes must have better thermal stability.
3. Room temperature and atmospheric pressure dyeable polyester (ECDP) fiber
The dyeable polyester ECDP at normal temperature and pressure can be prepared by adding a small amount of the fourth monomer in the process of ordinary pet polymerization. This is mainly because the polyethylene glycol flexible chain segment is introduced into the pet macromolecular chain, which makes the molecular structure of the fiber more loose and the amorphous region larger, which is more conducive to the entry of cationic dyes into the fiber and the combination with more sulfonic acid groups. Therefore, it can be dyed under normal pressure boiling dyeing conditions. ECDP fiber has softer hand feel and better wearability than CDP and PET fiber. However, due to the low 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, the fabric made of ECDP fiber should be paid special attention in the post-treatment, washing and ironing.
4. PTT fiber
PTT fiber is the abbreviation of polypropylene terephthalate fiber. Some people abroad call PTT the large fiber of the 21st century, and its trade name is “Corterra”.
PTT, pet and PBT belong to polyester family, and their properties are similar. PTT fiber has the characteristics of both polyester and nylon. It is as easy to wash and dry as polyester, has good elasticity recovery and crease resistance, and has good pollution resistance, light resistance and hand feel. It has better dyeing performance than polyester, and can be dyed under normal pressure. Under the same conditions, the penetration of the dye to 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 tensile recovery, and has the characteristics of large elasticity and good fluffy, so it is more suitable for making carpets and other materials.
5. PBT fiber
PBT fiber is the abbreviation of polybutylene terephthalate fiber. PBT fiber is made of dimethyl terephthalate (DMT) or terephthalic acid (TPA), the main raw material of polyester, and 1,4 – butanediol. PBT fibers were prepared by melt spinning of DMT and 1,4 – butanediol at high temperature and vacuum, using organic titanium or tin compounds and tetrabutyl titanate as catalysts. The polymerization, spinning, post-processing technology and equipment of PBT fiber are basically the same as those of polyester.
PBT fiber has the same characteristics as polyester fiber, such as good strength, easy washing and quick drying, stable size, good shape retention, etc. the most important thing is that the flexible part of its macromolecular chain is long, so it breaks and stretches, has good elasticity, has little change in elasticity after heating, and feels soft. Another advantage of PBT fiber is that its dyeability is better than that of polyester. The PBT fabric can be dyed with disperse dyes under the condition of boiling dyeing at atmospheric pressure. In addition, PBT fiber has good aging resistance, chemical resistance and heat resistance. PBT fiber is widely used in engineering plastics, household appliance shells and machine parts.
6. Pen fiber
Pen fiber is the abbreviation of polyethylene naphthalate fiber. Like polyester, pen fiber is a semi crystalline thermoplastic polyester material, which was initially introduced by KASA company of the United States. Its production process is through transesterification of dimethyl 2,6 – naphthalene dicarboxylate (NDC) and ethylene glycol (eg), and then polycondensation; Another method is direct esterification of 2,6 – naphthalene dicarboxylic acid (NDCA) and ethylene glycol (eg), and then polycondensation. The thermal stability of pen can be improved by adding a small amount of compounds containing organic amines and organic phosphorus.
The spinning process of pen fiber is similar to that of polyester. The process flow is: chip drying → high-speed spinning → drafting. As the glass transition temperature of pen fiber is higher than that of polyester fiber, the drafting process should be changed accordingly. Multi pass drafting should be adopted and the drafting temperature should be increased to avoid affecting the fiber quality due to the slow molecular orientation speed. Compared with conventional polyester, pen fiber has better mechanical and thermal properties, such as high strength, high modulus, good tensile resistance and high rigidity; Good heat resistance, stable size, not easy to deform, good flame retardancy; Good chemical resistance and hydrolysis resistance; UV resistance and aging resistance.
7. Wet and dry polyester filament
By changing the cross-section shape of the fiber, the gap between the single fibers is increased, the specific surface area is increased, and the capillary effect greatly improves its moisture conductivity, so as to make the wet and dry polyester filament. The fiber fabric has excellent moisture conductivity and moisture diffusion performance. It is matched with cotton fiber and other fibers with good moisture absorption. With a reasonable organizational structure, the effect is better. The clothing is dry, cool and comfortable. It is suitable for knitted sportswear, woven shirts, summer clothing fabrics, polyester stockings, etc.
8. High dehumidification four channel polyester fiber
Du Pont has developed a TEFRA – channel polyester fiber with excellent wicking capacity. It is a high moisture conducting fiber made of hydrophobic synthetic fiber, which can wick sweat from highly sweating skin to the fabric surface for evaporative cooling. The results showed that the moisture removal percentage of cotton fiber was 52% and that of four channel polyester fiber was 95% after 30min. This kind of fiber is especially effective in sports clothing and military lightweight thermal underwear, which can keep the skin dry and comfortable, and has excellent heat preservation and cold proof functions.
9. Polyester porous hollow section fiber “wellkey”
Wellkey’s development purpose is to take liquid sweat as the object to achieve complete sweat absorption and quick drying. Wellkey is a polyester hollow fiber. From the surface of the fiber, there are many pores penetrating into the hollow part. Liquid water can penetrate into the hollow part from the fiber surface. This fiber structure aims at the maximum water absorption rate and moisture content. In the spinning process, a special pore forming agent was blended and dissolved to form the fiber structure. The fiber has excellent perspiration absorption and quick drying characteristics, and is mainly used as the fabric of petticoats, tights, sportswear, shirts, training clothes, coats and other clothing. In addition, due to its advantages of water absorption and quick drying and low drying cost, it also has broad application prospects in non wearing fields and medical and health fields.
10. Three dimensional crimped hollow polyester fiber
The early three-dimensional crimp fiber was made by using two polymers with different shrinkage properties through composite spinning technology and specific cooling forming process. After drawing, it formed natural crimp due to the difference in shrinkage. The current preparation process has made great progress, that is, it adopts the unique patented technology of eccentric spinneret hole design, combined with asymmetric forming cooling system and corresponding subsequent drawing and shaping process, The prepared fiber has high curl degree, natural and permanent curl and good warmth retention. At present, the developed varieties include four hole, seven hole or even nine hole three-dimensional crimped hollow fibers. Three dimensional crimped hollow fiber is widely used in filling and thermal fiber fields.
Data collection: dyeing and finishing Encyclopedia
From: official account fabric course
Post time: Jun-21-2022