INFLUENCE OF PRIMARY QI ON PITCH PYROLYSIS WITH REFERENCE TO UNIDIRECTIONAL C C COMPOSITES/

The pyrolysis of four pitches of increasing quinoline insolubles (QI) content (0.5-11 wt%), prepared by blending, in different proportions, a commercial binder pitch with varying amounts of the same filtered pi tch (almost QI free), was studied by hot stage microscopy and thermogr avimetric analysis. Pyrolysis products of the pitches, obtained at 450 degrees C for 30 minutes, were examined by optical microscopy to moni tor the influence of QI on mesophase formation. The optical texture, c rack development, porosity and fibre/matrix bonding of the composites were considered in relation to the QI content of the pitch-matrix prec ursor. Bulk density, flexural strength and interlaminar shear strength of composites were explained in regard to their microstructure and th e composition of the pitch precursors. The restricted development of m esophase in the individual pitches was associated with the presence of QI and lead to the generation of intramatrix mosaics in the C/C compo sites, domains always being orientated around the fibre. QI improved f ibre/matrix bonding and the overall strength of the composites, but th e composites became more brittle. (C) 1998 Elsevier Science Ltd. All r ights reserved.