Patent Application
20140283348
This invention relates to fiber composites. More specifically, it relates to the recycling of composite material comprising fabric or sheets having fibers that have been pre-impregnated with an epoxy resin.
Fiber reinforced polymer (also called fiber reinforced plastic) has become a popular material for the fabrication of various products due to its strength, durability and relative light weight. Fiber reinforced polymer (FRP) is a composite material comprising a polymer material reinforced by glass, carbon, aramid or other types of fibers. Products constructed from FRP are fabricated using a variety of manufacturing methods including the use of fabric comprising fibers that have been pre-impregnated with a resin. This pre-impregnated fabric, or “pre-preg,” is typically produced in the form of sheets or rolls of woven or uni-directional fibers bound together by a partially cured resin, which is usually an epoxy. The resin is only partially cured so that the pre-preg maintains a solid but flexible shape.
A pre-preg sheet is usually tacky or sticky, which is a characteristic of the uncured resin. Pre-preg sheets often have backing film on both sides of the sheets to facilitate easy handling and storage of the tacky material. Because a pre-preg comprises resin that has already undergone some curing, the material has a limited shelf life and may require cold storage to prevent complete curing, since complete polymerization is most commonly achieved by heating the pre-preg. Composite structures built of pre-preg typically require an oven or autoclave to complete polymerization. Typically, pre-preg material is sold with a guarantee shelf life of approximately twelve months when stored at specified cool temperatures.
After the pre-preg is considered to be expired, it cannot be used for any primary structural applications. Expired pre-preg material is currently disposed after expiration of the pre-preg resin. The pre-preg expires because the resin begins to oxidize, but the fibers do not usually lose their mechanical strength. Pre-preg material may be made from fiberglass, carbon and/or para-aramid synthetic fibers (e.g. Kevlar®) with different fiber orientations (unidirectional or woven). Composite laminates are assemblies of layers of fibrous pre-preg materials, which can be joined to provide required engineering properties.
The present invention is directed to a method and apparatus for recycling expired pre-preg material by dissolving expired resin from the material using solvent and recovering solvent, resin and pre-preg fiber for later use.
Other and further objects, benefits, and advantages of the present invention will become known to those skilled in the art upon review of the Detailed Description which follows.
The Applicant respectfully asserts that the following written Specification fully facilitates an understanding of the method steps of the invention; that as a result of such facilitation of understanding, no finding should be made under MPEP 608.02, ¶ 6.23, ¶ 6.2301, or PCT Art. 7(2)(ii); that the subject matter admits of illustration for such facilitation; and that no drawing submission requirement should be imposed.
The invention comprises methods and materials that allow expired pre-preg material to be recycled. In an embodiment of the invention, the expired pre-preg materials are sprayed with a jet of solvent at room temperature to remove the resin. Solvents that may be used to remove various types of resin include acetone, toluene, acetonitrile, dimethylformamid, hexane and tetrahydrofuran. Using a method according to the present invention, the orientations of the fibers remain intact and no damage is caused to the fibers. Different types of fibers typically used to construct resin impregnated materials, e.g. fiberglass, carbon, and polyaramid synthetic fibers, with different fiber orientations, can be recovered with minimal loss of the fiber strength. This method can be employed for all known pre-pregs and resin systems. The recovered fibers may be recycled and reused to manufacture a pre-preg material with a desired resin system with no or minimal loss in strength and other desired properties when compared to new material of the same type. The resin and solvent are collected after treatment of pre-preg material according to the present invention. Substantially all of the solvent used in the method or process is recovered by an evaporation and condensation process and the collected resin can also be reused. Therefore, this invention provides a technology that may be characterized as “Green” and environmentally friendly compared to other existing recycling techniques.
In another embodiment of the invention, expired pre-preg material is loaded into an intake of a solvent tank, typically via rollers. The pre-preg material is conveyed through the solvent tank for a specified/pre-determined amount of time as required to remove a substantial amount of resin from the pre-preg fibers. The fibers are conveyed from the tank, again, typically via rollers. Excess solvent is squeezed from the fibers and may return to the solvent tank or to another container. If required or desired, the fibers may be conveyed for another pass through the same solvent tank, or through a subsequent solvent tank, in order to further remove traces of resin. Solvent tanks may be formed from solvent resistant materials such as stainless steel, glass, polytetrafluoroethylene or other operable materials. Typically, the fibers are then washed with water and dried using pressured air, heat or a combination thereof. The fibers are then typically roller and stored until required for shipping or use.
Fluid remaining in a solvent tank after extraction of resin from pre-preg material contains a mixture of solvent and resin. A solvent tank may be provided with an outlet proximate the bottom of the tank to allow the fluid mixture to flow through the outlet to a collection container, such as a flask. Either a simple distillation method and apparatus or a rotary evaporator apparatus and method may be used to separate the solvent from the resin. With either method, fluid in a collection container is typically heated at least to the boiling temperature of the solvent. Solvent vapor is channeled into a condenser where solvent vapors are condensed to liquid state and collected for recycling. Following separation of the solvent through evaporation, the collection container contains substantially only recovered resin which may also be recycled for further use.
While the principles of the method of the invention have been made clear in the above Detailed Description, those skilled in the art may make modifications to the method steps including their identity, character, and sequence of performance without departing from those principles. Accordingly, it is intended that the description be interpreted as exemplary and not in the limiting sense, and that the invention be given a scope commensurate with the appended claims.
This non-provisional patent application claims the benefit of and priority from U.S. provisional patent application No. 61/833,442 filed Jun. 10, 2013. The inventor disclosed in and applicant of said provisional application is the same person as the person who is disclosed as the inventor in and applicant of the instant application. The applicant asserts that method and process steps disclosed and described in the instant application are substantially identical to those disclosed in said provisional application.
