Opto-mechanical properties of fibres. Part 1. Optical properties and orientation of drawn polyethylene fibres

Changes in the structure of different drawn polyethylene (PE) fibres are st udied by the Becke' line method and interferometrically. The Becke' line me thod is used to study the changes in the optical properties of the skin lay er of PE undrawn fibres. A Pluta polarizing interference microscope is used to determine the mean refractive indices and mean birefringence of the dra wn fibres. Some structural parameters, such as optical orientation function , electric polarizability difference and isotropic polarizability (Delta al pha/3 alpha(o)), are determined. This last parameter is found to be constan t and depends only on the fibre structure. The number of molecules per unit volume and the distribution of segments at an angle with respect to the dr aw ratio are also determined. The generalized Lorentz-Lorenz equation given by de Vries is used to determine PE fibre structural parameters. A compari son between the experimental and those obtained using the Lorentz-Lorenz eq uation is given. A refractive index profile can assist fibre characterizati on. An empirical formula is suggested to correlate the changes in A, Delta n,f(theta) and theta with the draw ratio, and its constants are determined. Microinterferograms and curves are given for illustration. (C) 1999 Societ y of Chemical Industry.