Carbon fibers with surface modification

Abstract

Typical commercial surface treatments for continuous carbon fibers are often unavailable for discontinuous fibers. As such, there is little variety of chopped fiber surfaces leading to non-ideal coating solutions which result in poor interfacial compatibility between fibers and a composite matrix. A method of applying a highly effective coating using a high throughput technique for chopped carbon fibers. The method provides the ability to tune both the coating thickness and chemical functionality using processing parameters. The coatings are evaluated using X-ray photoelectron spectroscopy (XPS) for uniformity and composition. Using this technique, thermoplastic composites are highlighted showing an increase in interfacial shear strength (IFSS) of 25 MPa. This process shows promise for increasing the throughput of surface treatment of chopped fiber on the industrial scale.

1 . A method of modifying a surface of carbon fiber having a functional moiety, said method comprising steps of:
 (a) contacting the surface of the carbon fiber with a vapor phase containing a solvent and a silane capable of covalent bonding to the functional moiety on the surface of the carbon fiber; wherein said contacting step is conducted in a sealed container under vacuum pressure from the vapor pressure of the silane to up to 50662.5 Pa for a sufficient time to covalently bond at least some of said silane to the functional moiety on the surface of the carbon fiber; and   (b) exposing the carbon fiber produced in step (a) to a temperature of from about 25° C. to about 200° C. for a period of from about 1 minute to about 96 hours to crosslink at least some of the silane on the surface of the carbon fiber.   
     
     
         2 . Surface modified carbon fiber produced by the method of  claim 1 . 
     
     
         3 . The surface modified carbon fiber of  claim 2 , having an interfacial shear strength of an interface between the modified carbon fiber surface and a polymer matrix that is increased as compared to the interfacial shear strength of the surface of the same carbon fiber in neat, oxidized form without silanization and the same polymer matrix. 
     
     
         4 . The surface modified carbon fiber of  claim 3 , wherein the increase in interfacial shear strength is from about 1 MPa to about 100 MPa. 
     
     
         5 . The surface modified carbon fiber of  claim 3 , wherein the increase in interfacial shear strength is from about 13 MPa to about 38 MPa. 
     
     
         6 . The surface modified carbon fiber of  claim 3 , having an interfacial shear strength of an interface between the modified carbon fiber surface and the polymer matrix increased as compared to the interfacial shear strength of a surface of a carbon fiber having silane modified surface obtained by silanization using a silane solution at a pressure of 101325 Pa and the same polymer matrix. 
     
     
         7 . The surface modified carbon fiber of  claim 3 , having 1 to 10 layers of silane groups on the surface of the carbon fiber. 
     
     
         8 . The surface modified carbon fiber of  claim 3 , having a monolayer of silane groups on the surface of the carbon fiber. 
     
     
         9 . A polymer composite comprising the surface modified carbon fiber of  claim 3 . 
     
     
         10 . A surface modified carbon fiber comprising:
 a carbon fiber having an outer surface,   1-10 layers of silane groups on the outer surface of the carbon fiber.   
     
     
         11 . The surface modified carbon fiber of  claim 10 , wherein interfacial shear strength is increased by 1 MPa to 100 MPa as compared to the carbon fiber in an unmodified, neat, oxidized form. 
     
     
         12 . The surface modified carbon fiber of  claim 10 , wherein interfacial shear strength is increased by 13 MPa to 38 MPa as compared to the carbon fiber in an unmodified, neat, oxidized form. 
     
     
         13 . The surface modified carbon fiber of  claim 10 , wherein interfacial shear strength is increased by at least 25 MPa as compared to the carbon fiber in an unmodified, neat, oxidized form. 
     
     
         14 . The surface modified carbon fiber of  claim 10 , wherein the coupling agent used to surface modify the carbon fiber contains at least one hydrolysable alkoxy group attached to a silicon atom and the silicon atom is also attached to an organic functionality. 
     
     
         15 . The surface modified carbon fiber of  claim 14 , wherein the coupling agent is selected from the group consisting of (3-aminopropyl) trimethoxysilane, (3-aminopropyl) triethoxysilane, (3-acryloxypropyl) triethoxysilane, (3-triethoxysilyl) propyl succinic anhydride and ((chloromethyl) phenylethyl) trimethoxy silane. 
     
     
         16 . The surface modified carbon fiber of  claim 10 , having a surface concentration of silane molecules of greater than 1 wt. %. 
     
     
         17 . The surface modified carbon fiber of  claim 10 , wherein the oxygen concentration on an outer surface of the surface modified carbon fiber is increased compared to an oxygen concentration on the outer surface of the carbon fiber.