Toughening by polyetherimide(PEI) in bisphenol-A dicyanate(BPACY) matrix composite was investigated. Modification was achieved through two types of specimens having different morphology. One was a conventional semi-IPN matrix from solution blend impregnation. The other type was a concentration and morphology gradient matrix, that is, the PEI concentration decrease as the distance increases from the ply to ply interface. Catalyst was used for the matrix having gradient morphology to control the polymerization rate of BPACY.
The interlaminar fracture toughness of the carbon fiber-PEI modified BPACY composite was measured using double-cantilever- beam(DCB) and end-notch-flexure(ENF) methods, conventional semi-IPN and uncatalyzed gradient semi-IPN composites showed modest increase under Mode I, and Mode II loading, while significant increase was obtained in catalyzed gradient composite. With the observation of the fracture surfaces by scanning electron microscopy(SEM) and optical microscopy, interfacial adhesion between fiber and matrix was substantially improved at low PEI composition, and the neat PEI layer at ply to ply interface which remained undissolved was plastically deformed at high PEI composition. The result shows that concentration and morphology gradient structure has a beneficial influence on the interlaminar fracture toughness of carbon fiber composite.
