Opto-mechanical properties of fibres. Part 3. Structural characterization of uniaxial orientation in drawn poly(ethylene terephthalate) by means of optical parameters

Abstract

Changes in the structure of polyethyleneterephthalate (PET) (Egyptian woollen type) fibres, with strain produced by different stresses, are evaluated from optical and density measurements. Calculation of the optical parameters is carried out using two-beam interference fringes, and the density data are obtained from the resultant optical data. The results are utilized for calculating the virtual refractive index, the harmonic mean polarizability of the dielectric, the harmonic mean specific refractivity, the form birefringence and the number of monomeric units per unit volume. Relations between the structural parameters with different strains are given for these PET fibres. Calculations are also carried out to evaluate some other parameters and constants. A comparison between Hermans' optical orientation function formula and the corrected formula by de Vries is given. Microinterferograms and curves are given for illustration.