Abstract: Usually studies concerning the improvement of fracture resistance of epoxy based matrix composites only focus on the improvement of the interface epoxy matrix and fiber．In parallel to that‚ a usual way to improve the fracture toughness of epoxy resins consists in the addition of an initially miscible thermoplastic （such as polyetherimide） which at a particular conversion depending on composition and reaction temperature‚phase separates．The final morphology results from a competition between
the rates of phase separation and of epoxy reaction．In this work‚the effect of reinforcing fibers （glass and carbon） on the formation of the morphology of different epoxy systems toughened by an initially miscible polyetherimide is studied．The presence of fibers in these systems is found not to affect the phase separation process of the matrix‚but the final morphology of the system is changed．The modification of the morphology is found to be less related to the nature of the fiber．The viscosity of the dif-ferent components of the matrix is found to be the determinant factor in the formation of the morphology in the composites．

Key words: thermoplastic toughening thermoseting resin, fiber reinforced composite, epoxy resin, polyetherimide