Particle Toughening for Improving Fracture Toughness

Abstract

A curable prepreg ply formed by applying two outer resin films to the top and bottom surfaces, respectively, of a layer of resin-impregnated reinforcement fibers. The outer resin films contains insoluble toughening particles, and partially soluble or swellable toughening particles, but the resin matrix which impregnates the reinforcement fibers does not contain the same toughening particles. The insoluble toughening particles are insoluble in the resin matrix of the resin films upon curing of the prepreg ply. The partially soluble or swellabbe toughening particles are partially soluble or swellable in the resin matrix of the resin films upon curing of the prepreg ply, but remain as discreet particles after curing.

1 - 10 . (canceled) 
     
     
         11 . A method for fabricating a curable prepreg ply comprising:
 moving a continuous layer of reinforcement fibers along a longitudinal path which comprises a plurality of pressure nips, each pressure nip being formed by two opposing consolidating rollers;   bringing two inner resin films into contact with the moving layer of reinforcement fibers before the layer of reinforcement fibers passes through a first pressure nip such that one of the inner resin films is in contact with a top surface of the layer of reinforcement fibers and the other inner resin film is in contact with the bottom surface of the layer of reinforcement fibers;   moving with the layer of reinforcement fibers with the inner resin films thereon through the first pressure nip and a second pressure nip to press the inner resin films onto the top and bottom surfaces of the layer of reinforcement fibers so as to form a resin-impregnated fiber layer having a top surface and a bottom surface;   bringing two outer resin films into contact with the resin-impregnated fiber layer before the resin-impregnated fiber layer passes through a third pressure nip such that one of the outer resin films is in contact with the top surface of the resin-impregnated fiber layer and the other outer resin film is in contact with the bottom surface of the resin-impregnated fiber layer; and   moving the resin-impregnated fiber layer with the outer resin films thereon through the third pressure nip and a fourth pressure nip to press the outer resin films onto the top and bottom surfaces of the resin-impregnated fiber layer,   wherein   the inner resin films are formed from a first curable resin matrix comprising at least one thermoset resin, but is void of any toughening particles,   the outer resin films are formed from a second curable resin matrix comprising at least one thermoset resin, and a mixture of two different types of toughening particles: (i) insoluble toughening particles, and (ii) partially soluble or swellable toughening particles, and   said insoluble toughening particles are insoluble in the second resin matrix upon curing of the prepreg ply, and said partially soluble or swellable toughening particles are partially soluble or swellable in the second resin matrix upon curing of the prepreg ply, but remain as discreet particles after curing.   
     
     
         12 . A method for fabricating a composite structure comprising:
 forming a plurality of prepreg plies, each prepreg ply being formed by the method of  claim 11 ;   laying up the prepreg plies in a stacking arrangement to form a laminate structure; and   curing the laminate structure,   wherein the insoluble toughening particles are insoluble in the second resin matrix upon curing, and the partially soluble or swellable toughening particles are partially soluble or swellable in the second resin matrix upon curing, but remain as discreet particles after curing.   
     
     
         13 . The method of  claim 11 , wherein the second resin matrix comprises at least one epoxy resin, and said insoluble toughening particles are thermoplastic particles that are insoluble in epoxy resin upon curing of the epoxy resin. 
     
     
         14 . The method of  claim 11 , wherein the second resin matrix comprises partially soluble toughening particles, which are thermoplastic particles that decrease in volume by more than 5% upon curing of the prepreg ply, but remain as discreet particles after curing. 
     
     
         15 . The method of  claim 11 , wherein the second resin matrix comprises swellable toughening particles, which are thermoplastic particles that increase in volume by more than 5% prior to or during curing of the prepreg ply. 
     
     
         16 . The method of  claim 11 , wherein the second resin matrix comprises a combination of insoluble thermoplastic particles and swellable, crosslinked thermoplastic particles,
 said crosslinked thermoplastic particles comprising one of:   (a) a crosslinking network created by crosslinking a cross-linkable thermoplastic polymer having at least one reactive group with a cross-linking agent that is chemically reactive to the reactive group, and   (b) an inter-penetrating polymer network (IPN) comprising thermoplastic polymer chains intertwined with a separate cross-linking network, said IPN being created by reacting at least one compound having one or more reactive groups with a cross-linking agent that is chemically reactive to the one or more reactive groups, in the presence of a thermoplastic polymer.   
     
     
         17 . A method for fabricating a curable prepreg ply comprising:
 moving a continuous layer of reinforcement fibers along a longitudinal path which comprises a plurality of pressure nips, each pressure nip being formed by two opposing consolidating rollers;   applying a first curable resin in the form of a resin bead ahead of a first pressure nip as the layer of reinforcement fibers passes through the first pressure nip, wherein the resin content is controlled by altering the gap between the consolidating rollers of the first pressure nip to form a resin-impregnated fiber layer;   moving the resin-impregnated fiber layer through a second pressure nip;   pressing an outer resin film onto the top surface of the resin-impregnated fiber layer and an outer resin film onto the bottom surface of the resin-impregnated fiber layer by moving the the resin-impregnated fiber layer with the outer resin films thereon through pressure nips located downstream from the second pressure nip,   wherein   the outer resin films are formed from a second curable resin, which comprises at least one thermoset resin, and a mixture of two different types of toughening particles: (i) insoluble toughening particles, and (ii) partially soluble or swellable toughening particles,   said first curable resin comprises one or more thermoset resins, but is void of the same insoluble and partially soluble or swellable toughening particles, and   said insoluble toughening particles are insoluble in the second resin upon curing of the prepreg ply, and said partially soluble or swellable toughening particles are partially soluble or swellable in the second resin upon curing of the prepreg ply, but remain as discreet particles after curing.   
     
     
         18 . The method of  claim 17 , wherein the second resin matrix comprises at least one epoxy resin, and said insoluble toughening particles are thermoplastic particles that are insoluble in epoxy resin upon curing of the epoxy resin. 
     
     
         19 . The method of  claim 17 , wherein the second resin matrix comprises partially soluble toughening particles, which are thermoplastic particles that decrease in volume by more than 5% upon curing of the prepreg ply, but remain as discreet particles after curing. 
     
     
         20 . The method of  claim 17 , wherein the second resin matrix comprises swellable toughening particles, which are thermoplastic particles that increase in volume by more than 5% prior to or during curing of the prepreg ply. 
     
     
         21 . The method of  claim 17 , wherein the second resin matrix comprises a combination of insoluble thermoplastic particles and swellable, crosslinked thermoplastic particles,
 said crosslinked thermoplastic particles comprising one of:   (a) a crosslinking network created by crosslinking a cross-linkable thermoplastic polymer having at least one reactive group with a cross-linking agent that is chemically reactive to the reactive group, and   (b) an inter-penetrating polymer network (IPN) comprising thermoplastic polymer chains intertwined with a separate cross-linking network, said IPN being created by reacting at least one compound having one or more reactive groups with a cross-linking agent that is chemically reactive to the one or more reactive groups, in the presence of a thermoplastic polymer.