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

Abstract

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 (in the range 180–360 GPa), as a result of different processing conditions leading to different molecular orientation and the presence of density fluctuations along the fibre axis. It is found that the 360 GPa modulus fibre has a strain-induced Raman band shift value of −12 cm −1/% which is the highest reported value for aromatic polymer fibres such as PBO and p-aramids. The strain-induced Raman band broadening value of this fibre is the lowest among the fibres studied. Compressive strengths 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 compression, which is different from the behaviour of carbon fibres and a characteristic feature of PBO fibres. The relationship between the band broadening and fibre morphology is discussed in detail.