Polybutylene terephthalate (PBT) is polycondensed by esterification of dimethyl terephthalate (DMT) or terephthalic acid (TPA) and butylene glycol. In recent years, PBT fiber has been produced on a large scale due to its abundant raw materials and similar production process to polyester. The molecular formula of PBT is [(CH2)4OOCC6H4COO]n, which has 2 more methylene chains than PET molecules, and the backbone structure of the larger methylene molecules of PBT is helical, similar to the molecular structure of nylon, and the methylene chain segment is longer than that of PET, so the softness, abrasion resistance and elasticity of PBT fiber are similar to those of nylon, and its chemical properties are similar to those of PET fiber. Because the molecules of PBT fibers can move freely, PBT fibers have excellent tensile compression elasticity and wrinkle resistance. Compared with the poor dyeability of PET, the glass transition temperature of PBT is only 22°C, and it can be boiled at atmospheric pressure with disperse dyes without a carrier, but PBT has poor dimensional stability at high temperatures due to the presence of A-type and B-type crystalline deformation.
Due to PBT fiber's excellent resilience, mildew and moth resistance, good crimp elasticity, antistatic properties and dyeability, PBT fiber has a large number of applications in elastic clothing such as swimsuits, sportswear, ski wear, jumpsuits, dance tights, etc. Spandex is more expensive and has poor lightfastness and is easy to produce yellowing, while the elasticity of PBT fiber is second only to spandex and better than nylon, and it can completely replace spandex in some fabrics, such as in stretch jeans, spandex is usually used as elastic yarn, but the strength of spandex is low, and it is easy to break after wearing and rubbing for a long time, and the use of PBT fiber instead of spandex as elastic yarn can effectively improve the situation. Due to its wool-like feel, PBT fiber can be interwoven with cotton, linen, etc. as autumn and winter clothing in the wool industry, and is also an ideal imitation down and filling material.
In addition to being used as a textile material alone, the modification application of PBT fiber has also been researched and developed in many aspects in recent years. For example, PBT/PET composite spinning fiber not only has good spinnability, but also the fabric feels soft, high fluffy, easy to dye, which can be used as imitation wool fiber and can replace spandex; at this stage, the elasticity of PBT block copolymer fiber can reach 80% of spandex, and other properties are better than spandex, and the appearance of this fiber is similar to silk, and can be interwoven with silk into a special style fabric.