Opto-thermal properties of fibers. XV. A study of the drawing behavior of quenched poly(ethyleneterephthalates) fibers

Studies of the mechanical and optical properties of undrawn uniaxially stre tched polyester PET (Egyptian manufacture) fibers by annealing and cold dra wing were performed. The optical properties and strain produced in PET fibe rs at different conditions were measured interferometrically at room temper ature. A two-beam interferometric technique was used to determine refractiv e indices and birefringence of the investigated PET samples with strain pro duced by different stresses. Using a microstrain device attached to a micro scope stage and through the application of the appropriate mathematical equ ations, the refractive indices and the birefringence values were determined as a function of the draw ratios. The resulting data were utilized to calc ulate the polarizability per unit volume, the number of molecules per unit volume, Poisson's ratio, the strain optical coefficient, and several other parameters and constants. Also, some structural parameters are determined, such as form birefringence, the virtual refractive index, the harmonic mean polarizability of the dielectric, the harmonic mean specific refractivity, and the isotropic refractive index. The generalized Lorentz-Lorenz equatio n given by de Vries is used to determine PET fiber structure parameters. Co mparison between the results have been compared with Hermans' optical orien tation function. Relationships between the various optical parameters and t he draw ratios are plotted, and the effect of draw ratio on the refractive index profile is studied. Microinterferograms are given for illustration. ( C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1869-1880, 1999.