The present disclosure generally relates to carbon fibers and, more specifically, to methods of reclaiming carbon fibers from composite parts for re-use.
Carbon fiber composites are being increasingly used for part fabrication in a number of industries, such as the automotive, aerospace, and military industries. As carbon fiber composite materials are lightweight and high in strength, such materials offer a number of advantages including improved fuel efficiencies for machines using them without compromising part durability. Carbon fiber composite materials include a matrix and a reinforcement. The reinforcement includes woven or non-woven carbon fibers, while the matrix is a polymer resin, such as epoxy resin.
Many methods exist to fabricate carbon fiber composites. In a dry layup process, layers of dry, woven or non-woven carbon fibers are laid up in a stack, and a resin matrix is subsequently applied or infused into the carbon fiber stack. In a wet layup process, each carbon fiber layer is coated or impregnated with resin during the layup process. The laminate stack may then be consolidated and cured by placing the stack in a vacuum bag and applying pressure and heat. There are many other alternative methods to fabricate carbon fiber composites as well.
While effective, carbon fibers and composite parts formed therefrom may be very expensive, particularly depending on the weave of the carbon fibers, the curing time used to fabricate the part, as well as the size and complexity of the part. In addition, the recycling of waste carbon fiber composite parts is often precluded as such parts cannot be melted and remolded into new parts without significant degradation. Given that the carbon fibers in carbon fiber composite materials are deeply impregnated with resin, it may be difficult to efficiently extract the resin from the carbon fibers for reuse of the carbon fibers. Methods of extracting pure carbon fiber from waste carbon fiber composite parts for incorporation into new parts are wanting. U.S. Pat. No. 6,245,822 discloses a method of recycling resin from mostly metallic composite waste articles by treatment with a decomposing solvent, but does not specifically target carbon fibers for reclamation and recycling.
As many industries may benefit from significantly reduced manufacturing costs that may result from the reuse of carbon fibers obtained from waste composite parts, there is clearly a need for effective methods for reclaiming pure carbon fiber from waste composite parts in significant yields. The present disclosure addresses this and other problems of the prior art.
In accordance with one aspect of the present disclosure, carbon fiber reclaimed from a composite part is disclosed. The composite part may include the carbon fiber and a resin. The carbon fiber may be reclaimed from the composite part by a method comprising placing the composite part and a first solvent in an interior portion of a centrifuge insert that is defined by a wall having a plurality of perforations extending therethrough. The method may further comprise centrifuging the composite part and the first solvent contained in the centrifuge insert to allow extraction of the first solvent and at least a portion of the resin through the perforations of the centrifuge insert, and allowing the carbon fiber to collect in the interior portion of the centrifuge insert. The carbon fiber collected in the interior portion of the centrifuge insert may be at least partially separated from the resin.
In accordance with another aspect of the present disclosure, a method for reclaiming carbon fiber from a composite part that includes the carbon fiber and a resin is disclosed. The method may comprise placing the composite part and methyl acetate in an interior portion of a centrifuge insert. The centrifuge insert may have a double-conical shape and may be defined by a wall having a plurality of perforations extending therethrough. The method may further comprise centrifuging the composite part and the methyl acetate contained in the centrifuge insert to allow extraction of the methyl acetate and at least a portion of the resin through the perforations of the centrifuge insert. In addition, the method may further comprise allowing the carbon fiber to collect in the interior portion of the centrifuge insert. The carbon fiber collected in the interior portion of the centrifuge insert may be at least partially separated from the resin.
In accordance with another aspect of the present disclosure, a centrifuge insert for reclaiming carbon fiber from a composite part that includes the carbon fiber and a resin is disclosed. The centrifuge insert may comprise a wall defining the centrifuge insert, a center, and two ends on opposing axial sides of the centrifuge insert with respect to a longitudinal axis of the centrifuge insert. A radial diameter of the centrifuge insert may increase gradually from the center to each of the two ends such that the centrifuge insert has a double-conical shape. The centrifuge insert may further comprise a plurality of perforations extending through the wall, and an interior portion configured to contain the composite part and a solvent during centrifugation. The resin and the solvent may be extracted through the perforations during centrifugation of the composite part, leaving the carbon fiber at least partially separated from the resin in the interior portion.
These and other aspects and features of the present disclosure will be more readily understood when read in conjunction with the accompanying drawings.
Referring now to the drawings, and with specific reference to
Turning now to
Referring specifically now to
The centrifuge insert 20 may be designed to fit inside of a centrifuge 24, as shown in
During the centrifugation 23 of the pieces 14 and the first solvent 22, the first solvent 22 may soften the composite material, allowing at least a portion of the resin to be drawn out of the composite material and into the first solvent 22. In addition, the rotation 38 of the centrifuge insert 20 about its longitudinal axis 40 may cause the extraction 41 of the first solvent carrying at least a portion of the resin 30 through the perforations 28 of the insert 20 (see
When using methyl acetate as the first solvent, applicants have found sufficient resin extraction from carbon fiber composites after about four days of centrifugation at room temperature and at a rotation speed of about 100 rotations per minute (rpm) under a pressurized atmosphere of about 20 pounds per square inch (psi) of CO2. It will be understood, however, that the centrifugation time, temperature, rotation speed, and CO2 (or other gas) pressure may vary in practice depending on a number of considerations such as the degree of resin impregnation, the type of resin, the structure of the carbon fiber (woven, nonwoven, etc), the curing time of the composite part, the choice of solvent, and other conditions.
With reference to
After completion of the first centrifugation step 23, the carbon fiber 46 may be collected from the interior portion 18 of the insert 20 and placed in an ultrasonic cleaner 60 with a second batch of the first solvent, as depicted in
Turning now to
During the centrifugation 63, the second solvent 62 and any remaining resin 30 may be extracted 41 through the perforations 28 of the insert 20 and into the reservoir 44, as best shown in
Upon completion of the second centrifugation step 63, the carbon fiber may be collected from the interior portion 18 of the insert 20 to provide the purified, reclaimed carbon fiber 10 (see
If desired, the reclaimed carbon fiber 10 may be forged into one or more carbon fiber sheets 64 for re-use in product manufacturing. Forging of the reclaimed carbon fiber 10 into the carbon fiber sheet 64 may be carried out as shown in
Notably, applicants have found that carbon fiber sheets 64 fabricated from the reclaimed carbon fiber 10 according to the methods disclosed herein have nearly identical interfacial shear and tensile strengths as carbon fiber sheets forged from virgin carbon fiber (see Table 1), thus emphasizing the suitability of the reclaimed carbon fiber 10 for reuse.
1MPa = megapascals;
2Carbon fiber reclaimed according to the sample protocol of Example 1.
Waste carbon fiber composite material (˜3.5 pounds) was chopped into about one inch square pieces in a Ceselcan KF chopping machine. The chopped pieces were then centrifuged in methyl acetate in the centrifuge insert 20 disclosed herein for a period of about four days at ambient temperature, a rotation rate of about 100 rpm, and a carbon dioxide pressure of about 20 psi. Carbon fiber was collected from the centrifuge insert and sonicated at 25-50 Hz in methyl acetate at ambient temperature for about one hour in an Ultra Clean ultrasonic cleaner. Carbon fiber was collected from the ultrasonic cleaner and centrifuged in 2-methyl-tetrahydrofuran in the centrifuge insert for a period of about four hours at ambient temperature, a rotation rate of about 100 rpm, and a carbon dioxide pressure of about 20 psi. Carbon fiber was collected from the centrifuge insert and allowed to dry for a period of about one day to yield the purified, reclaimed carbon fiber (˜3 pounds).
It can be seen from the above that the teachings of the present disclosure may find wide industrial applicability in a variety of settings including industries seeking lower cost carbon fiber and carbon fiber composite materials. The technology disclosed herein provides an efficient method to reclaim carbon fiber from waste composite materials in high purity and recovery yields (>95%). Specifically, sonication and centrifugation in selected solvents are used to break-up and soften the composite material to allow the release of resin from the carbon fiber into the solvents, and allow the resin and solvents to be extracted from the solid carbon fiber. As disclosed herein, suitable solvents for this purpose may be methyl acetate and 2-methyl-tetrahydrofuran, both of which have the advantage of being biodegradable and reusable. The technology disclosed herein also provides a novel centrifuge insert specifically designed to optimize resin extraction from the carbon fiber during centrifugation. Namely, the centrifuge insert includes a double-conical shape that allows for a gradation of rotation speeds, as well as a perforated body with a gradation of hole sizes to improve resin extraction.
A flowchart showing a series of steps that may be involved in reclaiming pure carbon fiber from a waste composite part in accordance with the present disclosure is shown in
After sonication, the solid carbon fiber pieces may be collected and placed in the centrifuge insert 20 in a bath of a second solvent, such as 2-methyl-tetrahydrofuran (block 80). Centrifugation of the carbon fiber in the second solvent according to a next block 82 may cause extraction of the second solvent and any remaining resin from the carbon fiber through the perforations 28 of the insert 20 into the collection reservoir 44 (see
The method disclosed herein thus provides access to purified carbon fiber from composite waste parts in high yields, an achievement heretofore unknown by applicants. The reclaimed carbon fiber may be recycled and reused in new products as a way to provide more cost-effective carbon fiber composite parts. For example, as disclosed herein, applicants have shown that the reclaimed carbon fiber may be forged into new carbon fiber sheets with strength profiles nearly identical to the strength profiles of carbon fiber sheets made from virgin carbon fiber. It is expected that the technology disclosed herein may find wide industrial applicability in a wide range of areas such as, but not limited to, automotive, marine, military, aerospace, and electronic applications.