Increasing the toughness or damage resistance/tolerance of composites has been a consistent theme in recent materials development, and one of the major motivating forces behind development of thermoplastic composites and thermoplastic/thermoset blends.
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To this end, Dr. Paul Steiner has explored methods of “inhomogeneous toughening” of discrete layers or regions in the laminate. One reason this approach is interesting is that prepregging and other processing requirements limit the amount of thermoplastic that can be incorporated into a thermoset matrix, and thus the amount of toughening that can be imparted. American Cyanamid has developed a method of interleaving discrete thermoset prepreg and thermoplastic resin layers to enhance delamination resistance, but at a sacrifice of stiffness, which requires a thicker, heavier overall laminate.
Dr. Steiner obtained encouraging results with an intermediate approach, whereby thermoplastic PEEK and polyethersulfone (PES) particles were dispersed in thermoset cyanate ester resin mainly in the interlaminar region between prepreg plies. This was accomplished by using large enough thermoplastic resin particles (11 microns) to be trapped in the outer regions of the prepreg by the carbon-fiber fabric.