OPTOTHERMAL PROPERTIES OF FIBERS - XIII - EVALUATION OF THE FORM BIREFRINGENCE AND SOME OTHER STRUCTURAL PARAMETERS DUE TO THERMAL ANNEALING FOR POLYESTER (PET) FIBERS

In this work, changes in the structure of polyester [poly(ethylene-ter ephtalate) (PET)] fibers after annealing at constant temperature (120 and 140 degrees C) and different times were studied interferometricall y. The density of annealed PET fibers were measured by a system based on vibrating string. The Pluta polarizing interference microscope was used to determine the optical parameters of these fibers. The density and optical results were used to calculate the degree of crystallinity , the form birefringence, the number of monomeric units per unit volum e, harmonic mean polarizability of the dielectric, harmonic mean speci fic refractivity, and the virtual refractive index. The behavior of fi ber crystallinity at different annealing conditions were discussed wit h different optical parameters. Hermans optical orientation function h ave been compared with the generalized Lorentz-Loranz equation given b y de Vries. Microinterferograms and curves are given for illustration. (C) 1998 John Wiley & Sons, Inc.