What is the organizational structure of polyester fabrics?

What is the organizational structure of polyester fabrics?
1. Chemical structure The basic component of polyester is polyethylene terephthalate, with the molecular formula [-OC-Ph-COOCH2CH2O-]n, so it is also called polyester fiber (PET). The chemical structure of its long-chain molecule is H(OCH2CCOCO)NOCH2CH2OH, the relative molecular weight is generally about 18000~25000. In fact, there are still a small amount of monomers and oligomers. These oligomers have a low degree of polymerization and exist in cyclic form. Polyethylene terephthalate can be obtained by direct esterification of terephthalic acid (PTA) and ethylene glycol (EG) to obtain ethylene terephthalate (9BHET) and then polycondensation. 
From the perspective of polyester molecular composition, it is composed of short aliphatic hydrocarbon chains, ester groups, benzene rings, and alcohol-terminated hydroxyl groups. In addition to the presence of two alcohol-terminated hydroxyl groups in the polyester, there are no other polar groups, so the hydrophilicity of the polyester fiber is extremely poor. The polyester molecule contains about 46% ester groups. The ester groups can undergo hydrolysis and thermal cracking at high temperatures, and will be saponified when exposed to alkali, which reduces the degree of polymerization. Polyester molecules also contain aliphatic hydrocarbon chains, which can make the polyester molecules have a certain flexibility, but because there are benzene rings in the polyester molecules that cannot be rotated internally, the polyester macromolecules are basically rigid molecules, and the molecular chain is easy to maintain linearity. . Therefore, polyester macromolecules are easy to form crystals under this condition, so the crystallinity and orientation of polyester are relatively high. 

2. Physical structure The morphological structure of polyester made by melt spinning method observed in the microscope has a circular cross section and no special longitudinal structure. Filamentous fibril structure can be observed under the electron microscope. Shaped fibers can change the elasticity of the fibers, make the fibers have special luster and bulkiness, and improve the cohesion and covering ability of the fibers, as well as anti-pilling, reducing static electricity, etc. performance. For example, triangular fibers have a flashing effect. The five-lobed fiber has a fat-like luster, has a good feel, and resists pilling. The hollow fiber has low density and good warmth retention due to the cavity inside. 

3. The thickness of the polyester folded chain lamella measured by electron diffraction is about 10NM, and the length of the polyester single base is 1.075NM. Therefore, the thickness of the lamella can be considered to be equivalent to the single base length of 9 polyester molecules. . However, the polyester macromolecular chain length is about 1.075*130 (average degree of polymerization) = 140NM, which shows that the polyester lamella macromolecular chain must take a folded chain structure. Folding may occur at the -CH2-CH2- chain segment, because the chain is more flexible and easy to bend. In addition, because polyester macromolecules can also form straight chain crystals (fibrillated crystals). It can be seen that the internal folded chain crystals and fibril crystals coexist in polyester. The ratio of these two crystallizations varies with the stretching ratio and heat setting conditions.