An investigation into the relationship between processing, structure and properties for high-modulus PBO fibres. Part 1. Raman band shifts and broadening in tension and compression

This study is concerned with an investigation into the relationship between morphology and mechanical properties for poly(p-phenylene benzobisoxazole) (PBO) fibres performed using Raman spectroscopy. The three fibres studied have different modulus values tin the range 180-360 GPa), as a result of di fferent processing conditions leading to different molecular orientation an d the presence of density fluctuations along the fibre axis. It is found th at the 360 Cpa modulus fibre has a strain-induced Raman band shift value of -12 cm(-1)/% which is the highest reported value for aromatic polymer fibr es such as PBO and(l-aramids, The strain-induced Raman band broadening valu e of this fibre is the lowest among the fibres studied. Compressive strengt hs for the PBO fibres were also measured and found to be similar (0.29-0.35 GPa). It was also shown that the Raman band broadening becomes less in com pression, which is different from the behaviour of carbon fibres and a char acteristic feature of PBO fibres. The relationship between the band broaden ing and fibre morphology is discussed in detail. (C) 2000 Elsevier Science Ltd. All rights reserved.