Tensile and compressive deformation of polypyridobisimidazole (PIPD)-based'M5' rigid-rod polymer fibres

The tensile and compressive deformation behaviour of a new type of heterocy clic rigid-rod polymer fibre, polypyridobisimidazole 'PIPD' or 'M5', produc ed by the spinning of liquid-crystalline solutions, have been studied. The Young's moduli and tensile strengths for the two different PIPD or M5 fibre s have been determined to be greater than 300 GPa and 4 GPa, respectively. Molecular deformation in the fibres has been monitored using Raman spectros copy and it has been shown that the peak positions of the Raman bands in th e fibres are sensitive to the application of mechanical stress and strain. This has enabled a detailed study of molecular deformation to be undertaken for both tensile and compressive deformation. Full tensile-compression str ess-strain curves have been derived and the compressive modulus and compres sive strength of the PIPD fibres have been determined to be greater than 30 0 GPa and up to 1 GPa, respectively, which are both considerably higher tha n values for other high-performance polymer fibres. The potential use of PI PD fibres as reinforcing fibres in high-performance composites is discussed . (C) 1999 Elsevier Science Ltd. All rights reserved.