Opto-thermal properties of fibres: 5. Structure variations in nylon 66 fibres due to different thermal conditions

Abstract

Nylon 66 fibres were annealed at a temperature of 90–180°C for 6 h and quenched in coarse ice. Refractive indices and birefringence were measured interferometrically. Three independent techniques have been used to study the optical anisotropy in these fibres. The first technique is to study the geometrical parameters from the diffraction pattern using a He–Ne laser beam, the second is the application of two-beam interferometry to determine the mean refractive indices and double refraction of annealed samples. The third, acoustic method has been used for measuring the density and the mechanical loss factor of these fibres. The optical results data were used to calculate the mean polarizability per unit volume, the isotropic refractive indices, and optical orientation. The value of (Δ α/3 α 0) which depends upon the molecular structure of the polymer remains constant and is in agreement with previous published data. Behaviour of optical properties at different annealing conditions is discussed. The density results were used to calculate the degree of crystallinity of nylon 66 fibres. In addition, the resulting data were used to calculate the mean density fluctuation at different annealing conditions. The results obtained clarify the new reorientation and change occurring due to annealing at different conditions. The changes in the refractive index profile of annealed and quenched nylon 66 fibres at different conditions are given. Microinterferograms and curves are given for illustration.