HETEROGENEOUS PHASE-SEPARATION AROUND FIBERS IN EPOXY PEI BLENDS AND ITS EFFECT ON COMPOSITE DELAMINATION RESISTANCE/

Blends of difunctional epoxy with poly(ether imide) modifier were prep ared and combined with unidirectional (UD) glass-fibre tape to produce prepregs. These prepregs were laid-up, autoclave cured into UD fibre- reinforced composites and tested under mode I loading. The phase separ ation in the curing PEI/epoxy blends was studied by microscopic techni ques and was compared to that developing in the presence of individual glass, carbon and aramid fibres. During cure, a discrete epoxy-rich l ayer formed around glass fibres, caused by preferential wetting of the fibre by the epoxy phase. The extent of the epoxy-rich layer was foun d to be dependent on the PEI concentration in the blend and on the pro ximity of other fibres. No such layer was detected in the presence of carbon or aramid fibres. The presence of this discrete epoxy-rich laye r in the glass-fibre composite resulted in premature failure upon load ing and hence limited the benefit of the thermoplastic modification to the fracture resistance of the composite. (C) 1997 Elsevier Science L imited.