MOLECULAR DEFORMATION OF HIGH-MODULUS POLYETHYLENE FIBERS STUDIED BY MICRO-RAMAN SPECTROSCOPY

Raman spectra of the C-C stretching region of strained gel-spun ultradrawn ultrahigh-molecular weight polyethylene fibers were recorded. On the low-wavenumber side of both the asymmetric and symmetric band, an additional broad and appeared during straining of the fiber, indicating the presence of C-C bonds exhibiting high strain. The fraction of such C-C bonds was estimated to be 40%. At 4% strain, the shifts of the C-C stretching bands were found to increase linearly with the initial Young's modulus. From Raman spectra, information about strain distribution can be obtained. Considering the observed differences in strain distribution between fibers produced in a different way, it can be understood why one sample can be drawn to a higher extent without rupture of C-C bonds. The results were discussed in conjunction with results of X-ray measurements reported by Prasad and Grubb. It is suggested that the fibers can be described by two crystalline fractions mixed on the molecular level and an additional small amount of a third fraction with a low Young's modulus.