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Mechanical and structural parameters related to the optical properties of polyester (PET) (woollen type) fibres drawn at room temperature have been investigated. The changes in the strain were evaluated to obtain the molecular orientation factors 〈P2(cos θ)〉 and 〈P4(cos θ)〉. From the optical orientation, the values of f2(θ), f4(θ) and f6(θ) orientation parameters were calculated. The structure and properties of oriented PET have been studied in the light of the rubber elasticity theory. The dielectric constant, magnetic susceptibility, number N′ of chains between crosslinks per unit volume, optical configuration parameter and the segment anisotropy, were among the calculated parameters. The results of the extension were used to calculate the shrinkage factor. Relationships between the calculated parameters and the draw ratios, together with micro‐interferograms, are given for illustration. The present study throws light on how the applied stress changes the molecular orientation factors and the structural parameters. © 1999 Society of Chemical Industry

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A two-beam interferometric method is used to study the change of optical parameters of cold drawn boiled viscose fibers at different times. A stress-strain device conjugated to the Pluta polarizing interference microscope is used to investigate the dynamical behavior of opto-mechanical properties at room temperature. Some structural parameters such as the number of molecules per unit volume, the virtual and isotropic refractive indices, the optical orientation factor and angle, the strain and the stress optical coefficients are evaluated. Some mechanical parameters such as, Young's modules, elastic shear modules and the compressibility are calculated over different strain values. Also the number of network chain per unit volume N c , work per unit volume W, average work per chains WЈ, reduction in entropy ⌬S, and the optical configuration parameter ⌬␣ are determined. Also calculation of the constants of Moony-Rivilin equation are given. A systematic study over different wavelengths range extending from 405 to 590 nm was carried out to obtain the dielectric constant at infinity. The obtained results clarify that new reorientations occurred due to cold drawing at different conditions. Empirical formula is suggested to correlate the change in ⌬n, f( ), W, WЈ, A, , and N c with different draw ratio, and its constants were determined. Microinterferograms and curves are given for illustrations.