Optothermal properties of fibers?20?relation between physical structure and mechanical properties of cold drawn polypropylene fibers

Abstract

The structure of annealed polypropylene (PP) fibers is studied interferometrically using two-beam Pluta polarizing interference microscope connected to a device to study the draw ratio with birefringence changes dynamically. Relations of drawing changes with some optical and physical parameters are given. Evaluation of average work per chain, work per unit volume, reduction in entropy caused by elongation, and the work stored in the body as strain energy were determined. Also the resulting optical data were utilized to evaluate the orientation factor, the orientation angle, the virtual refractive index, and the number of molecules per unit volume. The value of (Δα/3α0), which depends upon the molecular structure of the polymer, remains constant. Relations between the physical and optical parameters with different strains are given for these fibers. The generalized Lorentz–Lorenz equation given by de Vries is used to determine polypropylene fiber structural parameters. Comparison between Hermans optical orientation function formula and the corrected formula by de Vries are given. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 819–831, 1999