The effect of hot multistage drawing on molecular structure and optical properties of polyethylene terephthalate fibers

In this work, mechanical and structural parameters related to the optical properties of polyethylene terephthalate (PET) fibers drawn at hot multistage have been investigated. The changes in optical parameters upon changing draw ratio are used to obtain the mechanical orientation factors and , various orientation functions f2(θ), f4(θ) and f6(θ), and amorphous and crystalline orientation functions (f a and f c). Also, the numbers of random links between the network junction points (N1), the average optical orientation (Fav), and the distribution function of segment ω(cos θ) were calculated. In addition, an empirical formula was suggested to correlate changes in the birefringence with the draw ratio and its constants were determined. The study demonstrated change on the molecular orientation functions and structural parameters upon hot multistage drawing. Significant variations in the characteristic properties of the drawn PET fibers were due to reorientation of the molecules caused by applied heat and external tension