Method of improving adhesion of carbon fibers with a polymeric matrix

• US 10,351,683 B2
• Filed: 05/18/2016
• Issued: 07/16/2019
• Est. Priority Date: 02/28/2012
• Status: Active Grant

• Current Assignee: UT-Battelle LLC
• Original Assignee: UT-Battelle LLC
• Inventors: Vautard, Frederic, Ozcan, Soydan, Paulauskas, Felix Leonard
• Primary Examiner(s): Penny, Tabatha L
• Application Number:
  US15/158,036
• Publication Number:
  US 20160257797A1
• Time in Patent Office: 1,154 Days
• Field of Search: 427333
• CPC Class Codes: C08J 2333/04 esters
• CPC Class Codes: C08J 2363/00 Characterised by the use of epoxy resins; Derivatives of epoxy resins
• CPC Class Codes: C08J 2463/00 Characterised by the use of epoxy resins; Derivatives of epoxy resins
• CPC Class Codes: C08J 5/06 using pretreated fibrous materials
• CPC Class Codes: C08L 63/10 Epoxy resins modified by unsaturated compounds
• CPC Class Codes: Y10T 428/249948 Fiber is precoated
• CPC Class Codes: Y10T 428/2918 including free carbon or carbide or therewith [not as steel]

Abstract

A method of making a carbon fiber having on its surface a partially cured sizing agent, the method comprising covalently binding on the surface of said carbon fiber a sizing agent comprised of an epoxy resin, and partially curing said sizing agent by contact thereof with a curing agent such that at least a portion of epoxide groups remain uncrosslinked on said surface, which corresponds to a curing degree of epoxide groups of no more than about 0.6, and further comprising reacting at least a portion of said epoxide groups with a bifunctional molecule that contains first and second reactive groups, the first reactive group being reactive with and forming a covalent bond with the epoxy group, and the second reactive group being unsaturated and accessible for reaction with a carbon-carbon double bond of an unsaturated resin via a vinyl addition reaction.

Claims

1. A method of making a carbon fiber having on its surface a partially cured sizing agent, the method comprising covalently binding on the surface of said carbon fiber a sizing agent comprised of an epoxy resin, and partially curing said sizing agent by contact thereof with a curing agent such that at least a portion of epoxide groups remain uncrosslinked on said surface, which corresponds to a curing degree of epoxide groups of no more than about 0.6, and further comprising reacting at least a portion of said epoxide groups with a bifunctional molecule that contains first and second reactive groups, the first reactive group being reactive with an epoxide group and thus forming a covalent bond with the epoxy group, and the second reactive group being unsaturated and reactive with a carbon-carbon double bond via a vinyl addition reaction, wherein said second reactive group is unreacted and accessible for reaction with a carbon-carbon double bond of an unsaturated resin.

2. The method of claim 1, wherein less than a stoichiometric amount of said curing agent is used.

3. The method of claim 1, wherein, prior to covalent binding of said sizing agent on the surface of the carbon fiber, said carbon fiber is surface-treated by a process that incorporates on said surface reactive functional groups that react with and form covalent bonds with said sizing agent.

4. The method of claim 3, wherein said reactive functional groups are selected from hydroxyl, carboxyl, and amine groups.

5. The method of claim 1, wherein said epoxy resin is comprised of a difunctional epoxy resin.

6. The method of claim 5, wherein said difunctional epoxy resin is selected from one or both of bisphenol A diglycidyl ether and ethylene glycol diglycidyl ether.

7. The method of claim 1, wherein said epoxy resin is a trifunctional or a higher functional epoxy resin.

8. The method of claim 1, wherein said curing agent is comprised of an organoamine containing at least two amine groups selected from primary and secondary amine groups.

9. The method of claim 1, wherein an amount of curing agent is selected that provides a curing degree of surface epoxide groups of no more than about 0.6.

10. The method of claim 1, wherein an amount of curing agent is selected that provides a curing degree of surface epoxide groups of no more than about 0.5.

11. The method of claim 1, wherein an amount of curing agent is selected that provides a curing degree of surface epoxide groups of no more than about 0.4.

12. The method of claim 1, wherein said partially cured sizing agent is a flexible gel.

13. The method of claim 1, wherein said sizing agent is made to covalently bind to the surface of the carbon fiber by, first, providing a carbon fiber containing on its surface groups reactive with said sizing agent to form a covalent bond with said sizing agent, and contacting said carbon fiber with a solution or emulsion of said sizing agent under conditions that cause the sizing agent to react with surface reactive groups and form covalent bonds with the carbon fiber, wherein said solution or emulsion is comprised of said sizing agent dispersed in a solvent carrier.

14. The method of claim 13, wherein said sizing agent is in an amount of up to 10% by weight in said solution or emulsion.

15. The method of claim 13, wherein said solvent carrier is aqueous.

16. The method of claim 13, wherein the sizing agent on the carbon fiber is selectively adjusted in thickness by corresponding selective adjustment in the concentration of the sizing agent in said solution.

17. The method of claim 1, wherein the sizing agent on the carbon fiber is selectively adjusted in viscosity by corresponding selective adjustment in the amount of curing agent used.