The basic composition of polyester fabric is polyethylene terephthalate, molecular formula [-OC-Ph-COOCH2CH2O-]n, so it is also called polyester fiber (PET), and the chemical structure formula of its long chain molecule is H(OCH2CCOCO )NOCH2CH2OH, the relative molecular weight is generally around 18000~25000. In fact, there are also small amounts of monomers and oligomers present. These oligomers have a low degree of polymerization and exist in a cyclic form. Polyethylene terephthalate can be produced by polycondensation of terephthalic acid (PTA) and ethylene glycol (EG) through direct esterification to obtain ethylene terephthalate (9BHET).
From the perspective of polyester molecular composition, it is composed of short aliphatic hydrocarbon chains, ester groups, benzene rings, and terminal alcohol hydroxyl groups. In addition to the existence of two terminal alcohol hydroxyl groups in polyester seeds, there are no other polar groups, so the hydrophilicity of polyester fibers is extremely poor. Polyester molecules contain about 46% ester groups. The ester groups can be hydrolyzed and thermally cracked at high temperature, and saponolyzed when encountering alkali, which reduces the degree of polymerization. Polyester molecules also contain aliphatic hydrocarbon chains, which can make polyester molecules have a certain degree of flexibility, but because there are benzene rings in polyester molecules that cannot rotate internally, polyester macromolecules are basically rigid molecules, and the molecular chain is easy to maintain a linear shape. . Therefore, polyester macromolecules are easy to form crystals under this condition, so the crystallinity and orientation of polyester are relatively high.