Single fibre deformation studies of poly(p-phenylene benzobisoxazole) fibres - Part I - Determination of Crystal Modulus

This paper constitutes the first part of a study to assess the influence of processing conditions on the final properties of poly(p-phenylene benzobis oxazole) PBO fibres. Three different samples were selected: as-spun (AS), h igh-modulus (HM), and ultra-high modulus (HM+) fibres. Synchrotron radiatio n was used to obtain single-fibre diffraction patterns. It is the first tim e this approach is taken to estimate the effects of deformation on the crys tal properties of PBO fibres. The crystal modulus of the different types of fibre was calculated from the variation with stress of the c-spacing deter mined from the shift of the (005) and (006) reflections. The HM fibre was f ound to have the highest crystal modulus of the three fibres, with AS and H M+ PBO being lower. In comparison with tensile data, none of the fibres wer e found to have a Young's modulus near to the crystal modulus value, althou gh the HM+ fibre was closest due to its production route. These results cou ld be compared to previous diffraction experiments, where the crystal modul us of PBO fibres were determined using fibre-bundles, assuming homogeneous stress in the bundle. Also, Raman spectroscopy experiments were carried out to examine the differences in Raman bandshift rates in response to both st ress and strain. The Raman results showed both the HM and HM+ fibres to hav e stress-induced bandshifts of approximately -4 cm(-1)/GPa. The AS fibre va lue was significantly lower, this being attributed to the non-uniformity of the fibre cross-section. The strain-induced Raman bandshifts were found to be dependent on the tensile modulus of the fibre. (C) 2001 Kluwer Academic Publishers.