Abstract
This study uses the optical results obtained by a double-beam interference polarized microscope connected to a mechanical device to measure the molecular orientation produced in polyester (PET) fibres. The samples were boiled for various periods oftime and stretched at room temperature. The changes in the molecular orientation were evaluated to obtain the values ofthree orientation functions. The results of the extension were used to calculate some mechanical factors and the shrinkage stress. In addition, the crystalline and amorphous orientation functions, the dielectric constant, the dielectric susceptibility and the number of moles of network chains per unit volume were among the calculated parameters. The present work throws light on how the thermal treatment and the applied stress affect the molecular orientation factors and the calculated structural parameters. Relationships among the calculated parameters and both the draw ratios and the boiling time are given. for illustration.