Composition and Molecular Structure of Polyester Fabric

The chemical name for polyester is polyethylene terephthalate (PET); it belongs to the class of aromatic polyester polymer compounds. Its basic structural unit is formed through the polycondensation reaction of terephthalic acid and ethylene glycol, and its molecular formula can be simplified to [C10H8O4]ₙ. For polyester intended for fiber production, the relative molecular weight typically ranges between 18,000 and 25,000; wool-like polyester variants generally possess lower molecular weights, while industrial-grade polyester variants tend to have relatively higher molecular weights.

The naming and classification of chemical fibers in textile products adhere to the standards stipulated in GB/T 4146.1-2009.

In terms of chemical composition, polyester macromolecules primarily consist of aliphatic chain segments (-OCH₂CH₂O-), ester groups (-COO-), benzene rings, and terminal hydroxyl groups. Ester groups account for approximately 46% of the molecule's content; aside from the terminal hydroxyl groups, the molecule lacks other hydrophilic polar groups. Consequently, the fiber exhibits strong hydrophobicity and extremely poor moisture absorption properties. Under high-temperature conditions, the ester groups may undergo thermal degradation; furthermore, in the presence of both high temperatures and water, hydrolysis reactions occur readily. Under strong alkaline conditions, saponification reactions may take place, leading to a reduction in the degree of polymerization; however, at temperatures below 100°C, standard concentrations of detergents generally have no significant adverse effect on polyester.

Regarding morphological structure, polyester fibers appear as smooth, uniform cylinders along their longitudinal axis, while their cross-sections are typically nearly circular. The nascent fibers produced via melt spinning possess an amorphous structure and exhibit relatively low mechanical properties; therefore, they must undergo drawing (orientation) and heat-setting treatments to meet practical application requirements. Finished polyester products are classified as semi-crystalline polymers, typically exhibiting a crystallinity level between 40% and 60%, along with a high degree of molecular orientation; these characteristics constitute the primary basis for the material's high strength, high modulus, and excellent dimensional stability. The benzene ring structures within the molecular chains impart a high degree of rigidity to the chain segments, thereby contributing to the material's strength and thermal resistance; conversely, the methylene chain segments (-OCH₂CH₂O-) provide a certain degree of flexibility, enabling the material to possess a balanced combination of robust mechanical properties and processability.