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

Nylon 66 fibres were annealed at a temperature of 90-180 degrees C for 6 h and quenched in coarse ice. Refractive indices and birefringence were measu red interferometrically. Three independent techniques have been used to stu dy 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 determin e the mean refractive indices and double refraction of annealed samples. Th e third, acoustic method has been used for measuring the density and the me chanical loss factor of these fibres. The optical results data were used to calculate the mean polarizability per unit volume, the isotropic refractiv e indices, and optical orientation. The value of (Delta alpha/3 alpha(0)) w hich depends upon the molecular structure of the polymer remains constant a nd is in agreement with previous published data. Behaviour of optical prope rties at different annealing conditions is discussed. The density results w ere used to calculate the degree of crystallinity of nylon 66 fibres. In ad dition, the resulting data were used to calculate the mean density fluctuat ion at different annealing conditions. The results obtained clarify the new reorientation and change occurring due to annealing at different condition s. The changes in the refractive index profile of annealed and quenched nyl on 66 fibres at different conditions are given. Microinterferograms and cur ves are given for illustration. (C) 1999 Elsevier Science Ltd. All rights r eserved.