Measurements to characterise the uniaxial orientation in nylon 6-6 fibres caused by thermal treatments

This paper gives relations between a number of optical properties of nylon 6-6 fibres annealed at various temperatures. Their mechanical loss factors, densities, crystallinities and mean square density fluctuations are presented. The densities and mechanical loss factors were determined using an acoustic method. The changes in molecular orientation were evaluated from the resulting optical data by using a polarizing Pluta interference microscope. Relationships are given between the optical parameters as a function of temperature for these fibres. The results obtained were utilized for calculations of the isotropic refractive indices and polarizabilities per unit volume, and relationships between these new parameters under various thermal conditions are given. The value of Delta alpha/3 alpha(o) (the ratio between the difference of the electric polarizability for one molecule and the isotropic polarizability) depends upon the molecular structure of the polymer and it remained constant. The results were used to calculate the form birefringence, virtual refractive index, harmonic mean polarizability of the dielectric, and the specific refractivity of the isotropic dielectric. The generalized Lorentz-Lorenz equation given by de Vries was used to determine nylon 6-6 fibre structural parameters. A comparison between the Hermans optical orientation function formula and the corrected formula by de Vries is given. The change in the refractive index profile of the annealed fibres is given. Illustrations are supplied using graphs and microinterferograms.