The basic constituent of polyester is polyethylene terephthalate, the molecular formula HO-H2C-H2C-O[-OC-Ph-COOCH2CH2O-]n, which is called polyester fiber because of the large amount of ester groups present in the molecular chain. The chemical structure of the long-chain molecule is H(OCH2CCOCO)NOCH2CH2OH, and the relative molecular weight of the polyester used for the fiber is generally about 18,000-25000. The molecular weight of the wool-like polyester is lower, and the molecular weight of the industrial polyester is higher. In fact, there are still a small amount of monomers and oligomers present. These oligomers have a low degree of polymerization and are present in a cyclic form. Polyethylene terephthalate can be obtained by polycondensation of terephthalic acid (PTA) and ethylene glycol (EG) by direct esterification to obtain ethylene terephthalate 9BHET).
From the molecular composition of polyester, it is composed of a short aliphatic hydrocarbon chain, an ester group, a benzene ring, and a terminal alcohol group. In addition to the presence of two terminal alcoholic hydroxyl groups in the polyester, there are no other polar groups, and thus the polyester fibers are extremely poor in hydrophilicity. The polyester molecule contains about 46% ester group. The ester group can be hydrolyzed and thermally cracked when it is above 200 °C. It will be hydrolyzed in the case of strong alkali, so that the degree of polymerization is lowered. The detergent detergent powder of 100 ° C or less does not have any polyester detergent. The polyester molecule also contains an aliphatic hydrocarbon chain, which can make the polyester molecule have a certain flexibility. However, since the polyester molecule has a benzene ring which cannot be rotated inside, the polyester macromolecule is basically a rigid molecule, and the molecular chain is easy to maintain. Line type. Therefore, the polyester macromolecule easily forms crystals under this condition, so the crystallinity and orientation of the polyester are high.