Raman spectroscopy of Kevlar 49 fibre

The Raman spectrum of poly(p-phenylene terephthalate) fibre, Kevlar 49, is reported. Fibre which had been exposed to heat, stress and radiation indicated that within experimental error, no general change takes place in the chemical structure of the material as a whole. However the spectrum of a filament under stress shows that all bands in the spectrum become increasingly polarized with increased stress. The spectral characteristics of the stress fibre lead to a possible explanation of the polymer's response to deformation — opening of the angles in the amide linkage of the polymeric chain and improved alignment of crystallites along the fibre axis.