Patent ID: 8796164

Claim:
An uncured structural composite material comprising a plurality of layers of structural fibers; a thermoset resin component; and an interlayer positioned between adjacent layers of structural fibers, the interlayer comprising at least two different types of nonwoven fibrous material, each nonwoven fibrous material comprising polymeric fibers, wherein the layers of structural fibers are impregnated with the thermoset resin component, said at least two different types of nonwoven fibrous material comprises a first nonwoven fibrous material located in a core portion of the interlayer and a second nonwoven fibrous material located in outer portions of the interlayer that are on either side of the core portion, the polymeric fibers of the first and second nonwoven fibrous materials are formed from a polymeric material comprising: (a) at least one thermoplastic elastomer, and (b) at least one thermoplastic polymer or copolymer thereof, the interlayer comprises a compositional gradient in which the first nonwoven fibrous material in the core portion differs in composition from the second nonwoven fibrous material in the outer portions, and the second nonwoven fibrous material is more permeable to the thermoset resin component than the first nonwoven fibrous material such that, upon curing, the interlayer comprises a resin interpenetration gradient in which the resin penetration in the outer portions of the interlayer is higher than that in the core portion.