Morphology, deformation and failure behaviour of homo- and copolyimide fibres 1. Fibres from 4,4 '-oxybis(phthalic anhydride) (DPhO) and p-phenylenediamine (PPh) or/and 2,5-bis(4-aminophenyl)-pyrimidine (2,5PRM)

The morphology, deformation and failure behaviour of new high-performance p olyimide (PI) fibres were examined by scanning electron microscopy (SEM), w ide angle X-ray diffraction (WAXD) and tensile measurements. PI fibres were prepared from rigid aromatic diamines p-phenylenediamine (PPh) and 2,5-bis (4-aminophenyl)-pyrimidine (2,5PRM) and semi-rigid 4,4'-oxybis(phthalic anh ydride) (DPhO) by wet-spinning of the N,N-dimethylacetamide solutions of th eir precursor poly(amic acids) in coagulation bath followed by thermal imid ization at 400 degrees C. The tensile properties and drawability of copolyi mide (coPI) fibres were better than those of homopolyimides (homoPI). The i mprovement in fibre modulus and tensile strength of the coPI fibres can be explained by the microblock structure on the X-ray level and composed morph ology on the macro level. Moreover, changes in the supermolecular structure and apparent fibril sizes, character of morphology, quantity of interfibri llar links, which affect the fracture mode were observed with the different composition of coPI. (C) 1999 Elsevier Science Ltd. All rights reserved.