Polyesters are those fibers containing at least 85% of a polymeric ester of a substituted aromatic carboxylic acid including but not restricted to terephthalic acid and f-hydroxybenzoic acid. The major polyester in commerce is polyethylene terephthalate, an ester formed by step growth polymerization of terephthalic acid and the diolethylene glycol.
Polyethylene terephthalate polyester is the leading man-made fiber in production volume and owes its popularity to its versatility alone or as a blended fiber in textile structures. When the term "polyester" is used, it refers to this generic type. It is used extensively in woven and knitted apparel, home furnishings, and industrial appl ications. Modification of the molecular structure of the fiber through texturizing and or chemical finishing extends its usefulness in various applications.
The cyclohexylene group within this fiber provides additional rigidity to the molecular chains, but the packing of adjacent polymer chains may be more difficult due to the complex structure (Figure 7-2). As a result, the fiber has a lower tenacity than polyethylene terephthalate.
The properties of this fiber were not sufficiently different from other
polyesters to achieve reasonable market penetration, and the fiber has been
Modified Terephthalate Polyesters
Poor dyeabi1ity and the moderate flammabi1ity of polyester have resulted in formulation of modified terephthalate esters to improve the dyeability and the flame retardant properties of the fiber.