The basic composition of polyester is polyethylene terephthalate, the molecular formula HO-H2C-H2C-O[-OC-Ph-COOCH2CH2O-]n, because there are a large number of ester groups on the molecular chain, it is called polyester fiber (PET ), the chemical structural formula of its long-chain molecule is H(OCH2CCOCO)NOCH2CH2OH. The relative molecular weight of polyester used for fibers is generally around 18000~25000, the molecular weight of wool-like polyester is lower, and the molecular weight of industrial polyester is higher. In fact, there are still small amounts of monomers and oligomers. These oligomers have a low degree of polymerization and exist in a cyclic form. Polyethylene terephthalate can be made by terephthalic acid (PTA) and ethylene glycol (EG) through direct esterification method to obtain terephthalate 9BHET) and then polycondensation.
From the molecular composition of polyester, it is composed of short aliphatic hydrocarbon chain, ester group, benzene ring and terminal alcoholic hydroxyl group. Except for the two terminal hydroxyl groups in the polyester, there are no other polar groups, so the polyester fiber is extremely poor in hydrophilicity. The polyester molecule contains about 46% ester groups. The ester groups can be hydrolyzed and thermally cracked when above 200 ℃, and they will be hydrolyzed in case of strong alkali, which will reduce the degree of polymerization. Impact; polyester molecules also contain aliphatic hydrocarbon chains, which can make polyester molecules have a certain degree of flexibility, but because polyester molecules also have benzene rings that cannot be rotated internally, polyester macromolecules are basically rigid molecules, and the molecular chain is easy to maintain Line style. Therefore, polyester macromolecules can easily form crystals under this condition, so the crystallinity and orientation of polyester are high.
