EFFECT OF ANNEALING ON THE OPTICAL AND MECHANICAL-PROPERTIES OF COLD DRAWN POLYPROPYLENE FIBERS

Refractive indices and birefringence changes with strain produced by d ifferent stresses in annealed and unannealed polypropylene fibres (4:1 draw ratio, 515 tex polypropylene from Bolton, UK) were measured inte rferometrically. Calculations were carried out using multiple-beam Fiz eau fringes in transmission to determine the Cauchy's constants, dispe rsive coefficient and the dielectric constant at infinity. The orienta tion factor and orientation angle of the fibre material were calculate d for different strain values. Poisson's ratio and the strain optical coefficient were also determined. An empirical formula is suggested to correlate the orientation factor, orientation angle, area of cross-se ction and birefringence with the draw ratio, and the constants of this formula were determined. The effect of the draw ratio on the refracti ve index profile was studied. Microinterferograms and curves are given as illustrations.