WO2016193927A1

WO2016193927A1 - Method of sizing carbon fibers, sized carbon fibers, and carbon fiber composites

Info

Publication number: WO2016193927A1
Application number: PCT/IB2016/053233
Authority: WO
Inventors: Abdullah-Al KAFI
Original assignee: Sabic Global Technologies B.V.
Priority date: 2015-06-05
Filing date: 2016-06-01
Publication date: 2016-12-08

Abstract

Sized carbon fibers, methods for the manufacture and use thereof, and carbon fiber polymer composites made from such compositions. In particular, sized carbon fibers are manufactured by a method including: contacting a plurality of carbon fibers with a sizing composition to form coated carbon fibers, wherein the sizing composition comprises a polyoxazoline sizing agent, preferably a poly[2-ethyl 2-oxazoline] sizing agent, dissolved in a solvent; and removing the solvent from the coated carbon fibers to form sized carbon fibers comprising the sizing agent.

Description

METHOD OF SIZING CARBON FIBERS, SIZED CARBON FIBERS, AND

CARBON FIBER COMPOSITES

BACKGROUND

[0001] Disclosed herein are water soluble sizing agents for use with carbon fibers, methods for sizing the carbon fibers, and uses thereof.

[0002] Composites comprising carbon fibers in a polymer matiix are widely used in industrial applications. The carbon fibers are often treated with a sizing agent during processing. The sizing agent can be selected to reduce static electricity, to maintain bundle (tow) integrity, to modify adhesion to the polymer, or to provide lubrication to protect both the carbon fibers and equipment during processing. A combination of these functions is often desired .

[0003] The carbon fibers are combined with the polymers by one of two methods, melt processing (compounding) or by solution processing, such as wet paper processing. The two methods have different requirements for formation of composites with good properties.

Compounding depends on melt distribution and wet-out, and for some polymers, requires sizing agents that are stable at high temperatures, for example up to 400°C. Wet paper processing depends on the coating surviving very high water ratios and high agitation. The method used to apply the sizing can therefore dictate the sizing agent used. For example, sizing agents for melt processing are often higher molecular weight oligomers that can withstand higher temperatures, while sizing agents for solution processing are lower weight, solvent-soluble emulsions. It would be preferable to select the sizing agent based on the type of carbon fiber being used, target polymer matrix, and the desired application.

[0004] Another limitation of current sizing formulations is that the sizing may need to be removed during processing. Sizing is generally applied after carbonization in the processing. It may need to be later removed, for example to permit application of another sizing, to improve electrical performance in the final products, to provide improved adhesion to a specific matrix, or to improve the modulus of carbon fiber. Often the sizing is difficult to remove by washing with water or solvent, or aggressive solvents and conditions must be used. For example the sizing may only be removable by heating the coated fiber to a high temperature under vacuum for a prolonged period, which is costly, time consuming, and may even degrade the fiber significantly.

[0005] Accordingly, there remains a need in the art for sizing agents and sizing agent compositions and that can be used for carbon fibers processed in either melt compounding or solution processing. There further remains a need for sizing that can be removed under mild conditions. A sizing having both of these characteristics would be particularly valuable.

SUMMARY

[0006] Disclosed herein is a method of manufacture of sized carbon fibers, the method comprising: contacting a plurality of carbon fibers with a sizing composition to form coated carbon fibers, wherein the sizing composition comprises a polyoxazoline sizing agent, preferably a poly[2-ethyi 2-oxazoline] sizing agent, dissolved in a solvent; and removing the solvent from the coated carbon fibers to form sized carbon fibers comprising the sizing agent in an amount of 0.01 to 1.2 weight percent based on the total weight of the sized carbon fibers, preferably 0.1 to 1.0 weight percent based on the total weight of the sized carbon fibers.

[0007] Also disclosed herein is a sized carbon fiber composition comprising: a plurality of carbon fibers comprising a coating comprising a polyoxazoline, preferably a polyoxazoline sizing agent, preferably a poly[2~efhyl 2-oxazoline] sizing agent, in an amount of 0.01 to 1.2 wt%, based on the weight of the sized carbon fibers.

[0008] Further disclosed herein is a method of producing a processed carbon fiber composition, the method comprising: providing the sized carbon fiber composition as disclosed herein; processing the sized carbon fiber composition; and at least partially removing the sizing from the processed, sized carbon fiber composition to produce the processed carbon fiber composition.

[0009] Also disclosed herein is a polymer composite comprising: the sized or processed carbon fiber composition as described herein; and a polymer.

[0010] The above described and other features are exemplified by the following detailed description.

DETAILED DESCRIPTION

[0011] The inventors hereof have discovered that carbon fibers can be sized by either melt compounding or by wet paper processing with small quantities (less than 1.2% by weight) of a polyoxazoline sizing agent, preferably a poly(2-ethyl-2-oxazoline) sizing agent. In a further advantageous feature, the sizing is readily removable with an aqueous solvent. The sizing improves the propensity of the fibers to be bundled into a tow that exhibits good handling properties during processing while also providing good spreading properties. In addition, the sizing is stable at higher temperatures, in particular temperatures as high as 400°C. It is also stable to chemicals and moisture, non-toxic, and available over a broad range of molecular weights.

[0012] In a preferred embodiment, the sizing agent is a polyoxazoline, specifically a poly(2-ethyl-2-oxazoline) (PEOX) having repeating units of formula (1).

[0013] Other polyoxazolines include poly[2-(Co-6 alkyl) 2-oxazoline]s, preferably poly[2-(Ci_6 alkyl) 2-oxazoline]s can be used as the sizing agent, including those including units of formula (2)

wherein R is hydrogen (a Co alkyl group) or a Ci_6 alkyl group optionally substituted with 1-3 halogens, nitrile, or nitro groups. Preferably, R is a Ci_3 alkyl group, most preferably ethyl. Methods for the manufacture of polyoxazolines, particularly PEOX, are known, and the polyoxazolines, particularly PEOX, can be obtained from a variety of commercial sources, i.e. Polymer Chemistry Innovations, Inc. in Tucson, Arizona, commercially known as AQUAZOL.

[0014] The polyoxazolines, particularly PEOX, can have a weight average molecular weight (MW) of 1,000 to 800,000 grams per mole (g/mol), preferably 2,000 to 600,000 g/mol, or 3,000 to 120,000 g/mol, or 3,000 to 100,000 g/mol, or 4,000 to 60,000 g/mol. In some embodiments the polyoxazolines, particularly PEOX, can have a weight average molecular weight of 3,000 to 200,000 g/mol, preferably 5,000 to 150,000 g/mol, or 10,000 to 120,000 g/mol. Polyoxazolines having a weight- average molecular weight less than 1,000 g/mole can have poor heat resistance, whereas polyoxazolines having a weight-average molecular weight greater than 800,000 g/mol may not be sufficiently soluble for smooth, even application to the fibers. In an embodiment, the molecular weight is selected to provide carbon fibers having the desired flexibility and a good balance between the bundling and spreading properties. Higher molecular weights provide higher bundling, but where the molecular weight is too high, the individual fibers being bundled so tightly during tow formation so as to reduce the spreadability of the tows. Lower molecular weights tend to provide lower bundling and higher flexibility.

[0015] In an important feature, the polyoxazolines are used in amounts effective to provide less than 1.2 weight percent (wt.%) of polyoxazoline based on the total weight of the sized carbon fibers. Use of higher amounts adversely affects the bundling and spreading properties of the sized fibers. As the amount of the sizing agent is increased, the propensity of the carbon fibers to be bundled into a tow is increased, thereby decreasing the flexibility of the fibers, and possibly impregnation of the fibers. Increased amounts of the sizing agent also adversely impacts easy removal of the sizing agent. As a lower limit, the amount of sizing agent is that effective to provide the desired sizing properties. For example, the sizing agent can be used in amount effective to provide 0.01 to 1.2 weight percent (wt.%) of sizing agent, or 0.05 to 1.1 wt.% of sizing agent, or 0.1 to 1.2 wt.% of sizing agent, each based on the weight of the sized carbon fibers. In a preferred embodiment, the sizing agent is used in amount effective to provide 0.1 to 1.0 wt.%, of sizing agent, based on the weight of the sized carbon fibers.

[0016] It is contemplated that the polyoxazolines are most useful as a solution in water or an aqueous solvent. However, if a solution or dispersion of the sizing agent is used, the average particle size of the dispersed sizing agent can be 5 micrometers (μπι) or smaller, for example 3 μτη or smaller, or 1 μπι or smaller. An aqueous dispersion containing the particles of the sizing agent having a particle size of greater than 5 μιη may not be practical because the sizing agent cannot be applied uniformly on reinforcement fiber and the dispersion is not stable during storage. Average particle size can be the average value calculated from, the particle size distribution determined with a laser diffraction/scattering particle size distribution measurement apparatus (LA-910, produced by Horiba, Ltd.).

[0017] Methods for making the solution, dispersion, or emulsion of the sizing agent is not specifically restricted and known methods can be used. For example method of sizing fibers comprises contacting a plurality of carbon fibers with a sizing composition to form coated carbon fibers. The sizing agents are thus applied as a solution, dispersion, or emulsion in a solvent. The solvent can be water, a protic polar organic solvent, an aprotic polar organic solvent, or a combination comprising at least one of the foregoing. Specific protic organic solvents include alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, pentanol, hexanoi, cyclohexanol, benzyl alcohol, and decanoi. Specific polar aprotic solvents include dioxane, tetrahydrofuran, γ-butyrolactone, 3-methyl-2-oxazolidone, ethylene carbonate, propylene carbonate, acetone, methyl ethyl ketone, acetonitrile, aniline, pyridine, N-methyl pyrrolidone, dimethyl acetamide, dimethyl formamide, 3-methyl-2-oxazolidone, hexamethyl phosphoric triamide, dimethyl sulfoxide, sulfolane, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, and ethylene glycol sulfite.

[0018] Preferably the solvent is an aqueous solvent comprising water and a water- miscible solvent can be used, for example methanol, ethanol, n-propanol, i-propanol, dioxane, tetrahydrofuran, acetone, or acetonitrile. The volume ratio of water:organic solvent can vary- widely, for example from 99: 1 to 10:90, or from 99: 1 to 50:50, or from 99:1 to 70:30. In an embodiment, the solvent is water, which is preferred for reasons of cost, each of the components constituting the sizing composition can beaded to water with agitation to be dispersed, emulsified or dissolved, or each of the components are mixed, heated to a temperature above their softening points, agitated in a homogenizer, mixer, or ball mill with mechanical shear, and emulsified through phase conversion by gradually adding water.

[0019] Preferably the sizing agent is dissolved or dispersed in the solvent (preferably water) as uniformly as possible. For example, in an embodiment the solution has such a turbidity that it transmits at least 10% of the light having a wavelength of 560 to 570 nm, at least 20%, or at least 30%.

[0020] The sizing agent can be present in the solvent in any amount effective to provide the desired weight of sizing agent on the carbon fibers. In an embodiment, the sizing composition comprises 0.01 to 40 wt.%, or 0.1 to 30 wt.%, or 0.5 to 20 wt.% of the sizing agent, each based on the total weight of the composition. In a preferred embodiment the sizing composition comprises 1 to 10 wt.% of the sizing agent based on the total weight of the composition.

[0021] Other components can be present in the sizing composition, for example a lubricant, a preservative, an antioxidant, a flame retardant, an antiseptic, a thixotropic agent, a titanate, a smoothing agent, a dispersing agent, a plasticizing agent, an antistatic agent, a dispersant, or the like, or a combination comprising at least one of the foregoing components. Each can be present in an amount of 0.01 to 5 wt.%, or 0.1 to 2 wt.%, or 0.01 to 1 wt.%, each based on the weight of the sizing agent in the sizing composition. An advantage of the polyoxazolines is that the compositions can easily applied, and good sizing properties can be obtained in the absence of the foregoing additives. Thus, in an embodiment, the sizing compositions contain none of the foregoing additives. In another embodiment, no dispersant, smoothing agent, or preservative is present.

[0022] All of the components of the sizing composition can be combined before applying to the carbon fibers, or the components can be separately applied to the carbon fibers in two or more steps. For efficiency, preferably ail of the components of the sizing composition are combined before applying to the carbon fibers.

[0023] The method of applying the sizing agent to the carbon fibers is not specifically restricted and any methods can used, for example spraying the carbon fibers with the sizing composition, impregnating the carbon fibers in the sizing composition, or immersing the carbon fibers, for example drawing the carbon fibers through the sizing composition with rollers.

Drawing with rollers allows uniform application for continuous carbon fibers. Preferably the sizing composition should be uniformly deposited on the fibers, which can be achieved by proper control of factors such as form, concentration, and temperature of the sizing composition, residence time in the sizing compositions, as well as the applied tension during application.

[0024] The sizing agent can be used with a wide variety of types of carbon fibers in various forms. The carbon fibers comprise graphite, expanded graphite, graphene, a pyrolyzed carbon fiber, a carbon nanotube, graphitized carbon black, or a combination comprising at least one of the foregoing types. The carbon fibers can be in a tow, knitted, braided, or in a mat that is woven or nonwoven. The fibers can be continuous or chopped. The dimensions of the fibers can vary greatly, and depend on the intended function of the fibers. For example, reinforcement fibers are often used in a form of chopped fiber cut into 1 to 15 mm long for manufacturing fiber-reinforced composites.

[0025] After the carbon fibers are contacted with the sizing composition, the solvent is removed, generally by drying. The drying method is not specifically restricted, and the sized carbon fiber strand can be air dried at ambient temperature, or heated and dried with heater rollers, hot airs, ovens, hot plates, or the like. Before or after drying, the coated or sized carbon fibers can be further processed by filament winding, knitting, braiding, weaving, or fabricated into a woven or nonwoven mat. The reinforcing fibers thus treated with the sizing agent can be stored, transported, or directly fed continuously to a composite manufacturing process.

[0026] The sized carbon fiber compositions produced by the above methods comprise a plurality of carbon fibers having a coating comprising the polyoxazoiine, specifically PEOX, in an amount of 0.01 to 1.2 wt.% of sizing agent, or 0.05 to 1.1 wt.% of sizing agent, or 0.1 1.2 wt.% of sizing agent, each based on the weight of the sized carbon fibers. In a preferred embodiment, the sizing agent is present in an amount of 0.1 to 1.0 wt.%, of sizing agent based on the weight of the sized carbon fibers. As used herein, a '"coating" can be a continuous or discontinuous layer disposed on the carbon fibers.

[0027] As stated above, an advantage of the polyoxazoiine sizing agents is their ready removal from the carbon fibers when desired. Thus, the carbon fibers can be sized, processed, and then treated to partially or fully remove the sizing before further storage, transport, or processing. There is no particular limit on the intermediate processing steps after obtaining the sized carbon fibers. For example, the processing can include one or more of storing the carbon fibers, heating the carbon fibers, weaving the carbon fibers, forming a mat or other shape from the carbon fibers, knitting the carbon fibers, braiding the carbon fibers, stitching the carbon fibers, making a prepreg from the carbon fibers, packaging the carbon fibers, transporting the carbon fibers, and the like.

[0028] To remove the sizing the processed, sized carbon fiber is contacted with a solvent under conditions effective to remove the sizing from the carbon fibers. The solvent can be any of those listed above for forming the sizing composition, in an embodiment, the solvent is water, and the contacting is at a temperature of 21 to 100°C, 40 to 90°C, or 50 to 70°C.

Contacting can be by any method, for example spraying the processed carbon fibers with the solvent, immersing the processed carbon fibers in the solvent, or drawing the carbon fibers through the solvent with rollers. Contacting is continued until the desired degree of removal is achieved.

[0029] The sized carbon fibers, or the processed carbon fibers with the poiyoxazoiine sizing agents at least partially removed can be used in a wide variety of applications. In an embodiment, the carbon fibers are used as a reinforcement fiber for a composite containing the carbon fibers disposed in a polymer matrix.

[0030] The polymer matrix can include one or more thermoplastic or thermoset polymers. Examples of thermoplastic polymers that can be used include polyacetals, polyacrylates, poiyacrylics, polyamideimides, polyamides, polyanhydrid.es, polyaramides, polyarylates, polyarylene ethers (e.g., polyphenylene ethers), polyarylene sulfides (e.g., polyphenyiene sulfides), polyarylsulfones, polycarbonates (including polycarbonate copolymers such as polycarbonate-siloxanes, polycarbonate-esters, and polyearbonate-ester-siloxanes), polyesters (e.g., polyethylene terephthalates and polybutylene terephthalates),

polyetheretherketones, poiyetherimides (including copolymers such as polyetherimide-siloxane copolymers), poiyetherketoneketones, polyetherketones, poiyefhersuifones, polyimides

(including copolymers such as polyimide-siloxane copolymers), polyolefins (e.g., polyethylenes, polypropylenes, polytetrafluoroethylenes, and their copolymers), polyphthalides, polysilazanes, polysiloxanes, polystyrenes including copolymers such as aciylonitrile-butadiene-styrene (ABS) and methyl methacrylate-butadiene-styrene (MBS), polysuifides, polysulfonamides, polysulfonates, polysulfones, polythioesters, polytriazines, polyureas, polyvinyl alcohols, polyvinyl esters, polyvinyl ethers, polyvinyl halides, polyvinyl ketones, poly vinylidene fluorides, silicones, or the like, or a combination comprising at least one of the foregoing thermoplastic polymers. Polyacetals, polyamides (nylons), polycarbonates, polyesters, polyetherimide, polyoiefins, and polystyrene copolymers such as ABS, are especially useful in a wide variety of articles, have good processability, and are recyclable. Examples of thermoset polymers include epoxies, phenoiics, and polyurethanes.

[0031] As stated above, an advantageous feature of carbon fibers sized with

polyoxazoline sizing agents is that the fibers can be processed by either melt compounding or solvent processing. Thus, the manufacturing method of the composite is not restricted, and can include filament-winding processes, a prepreg processes, sheet-molding processes, powder deposition processes, or molding, for example injection molding processes. Thus, the polymer or prepolymer composition (i.e., a curable thermosetting composition) can be in the form of a dry polymer powder composition, a melted thermoplastic polymer composition, or other form of polymer. When processing carbon fibers by any of the foregoing methods melt compounding or solvent processing, the concentration or sizing agent can be adjusted as described herein.

[0032] In processes using melt compounding, the carbon fibers are generally combined with the solid or the molten polymer, for example in an extruder. For example, powdered thermoplastic polymer, and other optional components are first blended, optionally with the carbon fibers or any other fillers, in a high speed mixer or by hand mixing. The blend is then fed into the throat of an extruder via a hopper. Alternatively, the carbon fibers can be incorporated into the polymer by feeding it directly into the extruder at the throat and/or downstream through a sidestuffer, or by being compounded into a masterbatch with a desired polymer and fed into the extruder. The extruder is generally operated at a temperature higher than that necessary to cause the composition to flow. The composition can be extruded to provide a desired shape, or the extrudate can be immediately quenched in a water bath and pelletized. Such pellets can be used for subsequent molding, shaping, or forming, in an alternative melt process, the fibers (e.g., fibers in the form of a mat) are impregnated with molten polymer, and cooled.

[0033] In solution processing, the fibers can be impregnated with a solution comprising the polymer, and the solvent subsequently removed. The solution can be effective to dissolve the polymer, but not the sizing agent. Alternatively, the solution processing can be a wet paper process, comprising contacting the carbon fibers with a particulate polymer dispersed in an aqueous solvent, followed by consolidating the particular polymer to prove the polymer composite. Wet paper processing generally produces a prepreg that can be used in further manufacturing steps. A number of binding agents for producing prepregs are known, for example organic materials such as sugar or synthetic polymers such as polyvinyl alcohol, use of a polyoxazoline sizing agent such as PEOX produces a prepreg that can withstand subsequent processing at high temperatures, for example up to 400°C. Articles produced from these prepregs accordingly have fewer defects associated with the degradation of binders that degrade at these temperatures,

[0034] Alternatively, a dry particulate polymer, i.e., a dry polymer powder can be used. The composite can be manufactured by combining the sized or processed carbon fiber composition with the dry polymer powder by known methods of powder coating or impregnation. An example of a powder impregnation method is the "D-Preg" technology available from Fibroline, which utilizes a system of two spaced, face-to-face electrodes connected to an alternative high tension generator. The powder is applied to the carbon fibers, which are placed between the two electrodes, and an alternative electric field is created to impregnate the fibers. The polymer powder is subsequently consolidated by heat, for example by passing the powder-coated carbon fibers through a heated roller, heating in an oven, or other method. This method can be used to produce a unidirectional thermoplastic tape, for example. Other powder deposition methods can also be used.

[0035] Other methods of processing include contacting the sized or processed carbon fiber composition with a thermosetting polymer precursor composition by any of the above methods, particularly solution or powder processing; and curing the thermosetting polymer precursor composition to provide the polymer composite. The curing can be by heat, chemical cure, or radiation cure. For example, the precursor composition comprising the carbon fibers can be reaction injection molded. Alternatively, during powder processing where the powder is a prepolymer composition, curing the prepolymer composition can be performed by heating the deposited powder under conditions effective to cure and consolidate the powder onto the sized or processed carbon fibers.

[0036] The amount of carbon fibers contained in a fiber-reinforced composite can vary widely and is selected according to the type and form of carbon fiber, the type of polymer matrix, and the intended use of the composite. For example, the amount of carbon fiber in a composite can be 0.01 to 80 wt.% based on the total weight of the composite, or 0.01 to 60 wt.% based on the total weight of the composite, or 0.01 to 50 wt.% based on total weight of the composite.

[0037] The polyoxazoline sizing agents accordingly provide flexibility in processing. The sizing agents can further be removed under mild conditions. The sizing agents have excellent wetting properties and impregnation properties for fiber surfaces, as well as for polymer matrices. Hence, composites compounded with the sized fibers can he free of voids and have improved mechanical properties. The poiyoxazoline sizing agents can further be processed at temperatures consistent for use with high-performance polymers such as polyetherimides, polyphenylene sulfones, and the like. A further advantage is that the poiyoxazoline sizing agents are stable over periods of storage, including under high humidity conditions that can cause hydrolysis of other sizing agents.

[0038] The following examples are provided by way of further illustration, and should not be construed as limiting.

EXAMPLES

Example 1

[0039] A sub-micrometer carbon fiber paper or tow was sized by spraying with a 1 wt.% water solution of PEOX (AQUAZOL 5, Polymer Chemistry innovations, Inc., Tucson, Arizona, MW = 5000 g/mole), then air-dried at 50°C in an oven. The resulting carbon fiber tow was slightly stiff, and easy to handle (easy to cut, transport, and consolidate), and the sizing agent can be removed after consolidation with warm water.

Example 2

[0040] A sub-micrometer carbon fiber paper or tow was sized by spraying with a 0.5 wt.% water solution of PEOX (AQUAZOL 5, Polymer Chemistry Innovations, Inc., Tucson, Arizona, MW = 5000 g/mole), then air-dried at 50°C in an oven. The resulting tow was less stiff than the above, and easy to handle (cut, transport, and consolidate), and the sizing agent can be removed after consolidation with warm water.

Example 3

[0041] A sub-micrometer carbon fiber paper or tow was sized by spraying the paper with a 1 wt.% water solution of PEOX (AQUAZOL 50, Polymer Chemistry Innovations, Inc., Tucson, Arizona, MW = 50,000 g/mole), then air-dried at 50°C in an oven. The resulting tow was stiffer, and more difficult to handle (cut, transport, and consolidate) than the tow made with MW 5000 PEOX, and the sizing agent can be removed after consolidation with warm water.

Example 4

[0042] A sub-micrometer carbon fiber paper or tow was sized by spraying with a 0.5 wt.% water solution of PEOX (AQUAZOL 50, Polymer Chemistry Innovations, Inc., Tucson, Arizona, MW = 50,000 g mole), then air-dried at 50°C in an oven. The resulting tow was less stiff, and easy to handle (easy to cut, transport, and consolidate) than the above, and the sizing agent can be removed after consolidation with warm water.

Example 5

[0043] A sub-micrometer carbon fiber paper or tow was sized by spraying with a 1 wt.% water solution of PEOX (AQUAZOL 200, Polymer Chemistry Innovations, Inc., Tucson, Arizona, MW = 200,000 g/mole), then air-dried at 50°C in an oven. The resulting tow was stiffer, and more difficult to handle (cut, transport, and consolidate) than the tow made using PEOX having a molecular weight of 5000 or 50,000, and the sizing agent can be removed after consolidation with warm water.

Example 6

[0044] A sub-micrometer carbon fiber paper or tow was sized by spraying with a 0.5 wt.% water solution of PEOX (AQUAZOL 200, trademark of Polymer Chemistry Innovations, Inc., Tucson, Arizona, MW = 200000 g/mole), then air-dried at 50°C in an oven. The resulting tow was less stiff, and less difficult to handle (cut, transport, and consolidate) than the mat made using the 1 wt.% water solution of Example 5, and the sizing agent can be removed after consolidation with warm water.

Example 7

[0045] A sub-micrometer carbon fiber paper or tow was sized by spraying with a 1 wt.% water solution of PEOX (AQUAZOL 500, Polymer Chemistry Innovations, Inc., obtained from PCI, Tucson, Arizona, MW = 500,000 g/mole), then air-dried at 50°C in an oven. The resulting tow was the stiffest, and most difficult to handle (cut, transport, and consolidate) among all the examples and the sizing agent can be removed after consolidation with warm water.

Example 8

[0046] A sub-micrometer carbon fiber paper or tow was sized by spraying with a 0.5 wt.% water solution of PEOX (AQUAZOL 500, Polymer Chemistry Innovations, Inc., Tucson, Arizona, MW = 500,000 g/mole), then air-dried at 50°C in an oven. The resulting tow was less stiff, and easier to handle (easy to cut, transport, and consolidate) than the 1 % MW 500000 example, and the sizing agent can be removed after consolidation with warm water. [0047] The invention is further illustrated by the following embodiments, which are not intended to limit the claims.

[0048] Embodiment 1. A method of manufacture of sized carbon fibers, the method comprising: contacting a plurality of carbon fibers with a sizing composition to form coated carbon fibers, wherein the sizing composition comprises a polyoxazoline sizing agent, preferably a poly[2-ethyl 2-oxazoiine] sizing agent, dissolved in a solvent; and removing the solvent from the coated carbon fibers to form sized carbon fibers comprising the sizing agent in an amount of 0.01 to 1.2 weight percent based on the total weight of the sized carbon fibers, preferably 0.1 to 1.0 weight percent based on the total weight of the sized carbon fibers.

[0049] Embodiment 2. The method of Embodiment 1 , wherein the contacting is by spraying the carbon fibers with the sizing composition, immersing the carbon fibers in the sizing composition, or drawing the carbon fibers through the sizing composition.

[0050] Embodiment 3. The method of any one or more of Embodiments 1 to 2, wherein the carbon fibers are continuous fibers.

[0051] Embodiment 4. The method of any one or more of Embodiments 1 to 3, wherein the carbon fibers are chopped fibers.

[0052] Embodiment 5. The method of any one or more of Embodiments 1 to 4, wherein the carbon fibers are woven, knitted, braided, or nonwoven.

[0053] Embodiment 6. The method of any one or more of Embodiments 1 to 5, wherein the carbon fibers comprise graphite, expanded graphite, graphene, a pyroiyzed carbon fiber, or a combination comprising at least one of the foregoing.

[0054] Embodiment 7. The method of any one or more of Embodiments 1 to 6, wherein the sizing agent has a molecular weight of 1 ,000 to 800,000 g/mol , preferably 2,000 to 600,000 g/mol, or 3,000 to 120,000 g/mol, or 3,000 to 100,000 g/mol, or 4,000 to 60,000 g/mol.

[0055] Embodiment 8. The method of any one or more of Embodiments 1 to 7, wherein the solvent is water, a protic polar organic solvent, an aprotic polar organic solvent, or a combination comprising at least one of the foregoing, preferably an aqueous solvent.

[0056] Embodiment 9. The method of Embodiment 8, wherein the solvent is water.

[0057] Embodiment 10. The method of any one or more Embodiments 1 to 9, wherein the sizing composition comprises 1 to 40 weight percent, preferably 1 to 30 weight percent, or I to 20 weight percent, or 1 to 10 weight percent of the sizing agent.

[0058] Embodiment 1 1. The method of any one or more of Embodiments 1 to 10, wherein the sizing composition further comprises a lubricant, a preservative, an antioxidant, a flame retardant, an antiseptic, a thixotropic agent, a titanate, a smoothing agent, a dispersing agent, a plasticizing agent, an antistatic agent, a dispersant, or a combination comprising at least one of the foregoing.

[0059] Embodiment 12. A sized carbon fiber composition produced by method of any one or more of Embodiments 1 to 11.

[0060] Embodiment 13. A sized carbon fiber composition comprising: a plurality of carbon fibers comprising a coating comprising a poly[2-(Co-6 alkyl)-2-oxazoline], preferably a poly[2-ethyl 2-oxazoline] sizing agent, in an amount of 0.01 to 1.2 wt%, based on the weight of the sized carbon fibers.

[0061] Embodiment 14. The sized carbon fiber composition of Embodiment 13, wherein the sizing agent has a molecular weight of 1,000 to 800,000 g/mol, preferably 2,000 to 600,000 g/mol, or 3,000 to 120,000 g/mol, or 3,000 to 100,000 g/mol, or 4,000 to 60,000.

[0062] Embodiment 15. A method of producing a processed carbon fiber composition, the method comprising: providing the sized carbon fiber composition of any one or more of Embodiments 1 to 14; processing the sized carbon fiber composition; and at least partially removing the sizing from the processed, sized carbon fiber composition to produce the processed carbon fiber composition.

[0063] Embodiment 16. The method of Embodiment 15, wherein the processing comprises storing the carbon fibers, transporting the carbon fibers, heating the carbon fibers, shaping the carbon fibers, weaving the carbon fibers, knitting the carbon fibers, braiding the carbon fibers, stitching the carbon fibers, making a prepreg from the carbon fibers, packaging the carbon fibers, transporting the carbon fibers, or a combination comprising at least one of the foregoing.

[0064] Embodiment 17. The method of any one or more of Embodiments 15 to 16, wherein removing comprises contacting the processed, sized carbon fiber composition with a solvent under conditions effective to remove the sizing from the carbon fibers.

[0065] Embodiment 18. The method of Embodiment 17, wherein the solvent is water, and the contacting is at a temperature of 21 to 100°C, 40 to 90°C, preferably 50 to 70°C.

[0066] Embodiment 19. A processed carbon fiber composition produced by any one or more of the methods of Embodiments 15 to 18.

[0067] Embodiment 20. A method of manufacturing a polymer composite, the method comprising: contacting the sized or processed carbon fiber composition of any one or more of Embodiments 1 to 19 with a thermoplastic polymer composition to provide the polymer composite. [0068] Embodiment 2,1. The method of Embodiment 20, wherein contacting comprises contacting the sized or processed carbon fiber composition with a molten thermoplastic polymer composition.

[0069] Embodiment 22. The method of Embodiment 20, wherein contacting comprises: contacting the sized or processed carbon fiber composition with a dry particulate thermoplastic polymer composition; and heating the contacted dry polymer powder to consolidate the particulate thermoplastic polymer composition.

[0070] Embodiment 23. The method of Embodiment 20, wherein contacting comprises: contacting the sized or processed carbon fiber composition with a particulate polymer composition dispersed in an aqueous solvent; and consolidating the contacted fibers to provide the polymer composite.

[0071] Embodiment 24. A method of manufacturing a polymer composite, the method comprising: contacting the sized or processed carbon fiber composition of any one or more of Embodiments 1 to 19 with a polymer precursor composition; and curing the contacted thermosetting polymer precursor composition to provide the polymer composite.

[0072] Embodiment 25. The method of Embodiment 24, wherein curing the polymer precursor composition on the sized or processed carbon fiber composition comprises heating the contacted fibers.

[0073] Embodiment 26. The method of Embodiment 24, wherein contacting comprises contacting the sized or processed carbon fiber composition with a particulate polymer precursor composition dispersed in an aqueous solvent; and curing the contacted polymer precursor composition comprises heating the contacted fibers under conditions effective to cure and consolidate the particulate polymer precursor composition.

[0074] Embodiment 27. The method of any one or more of Embodiments 20 to 26, wherein the sized or processed carbon fibers are present in an amount of 0.01 to 80 weight percent, preferably 0.1 to 60 weight percent, or 0.01 to 50 weight percent of the combined weight of the sized or processed carbon fibers and the polymer.

[0075] Embodiment 28. A polymer composite made by the method of any one or more of Embodiments 20 to 27.

[0076] Embodiment 29. A polymer composite comprising: the sized or processed carbon fiber composition of any one or more of Embodiments 1 to 19; and a polymer.

[0077] Embodiment 30. 'The polymer composite of Embodiment 29, in the form of unidirectional tape comprising a thermoplastic polymer matrix. [0078] Embodiment 31. The method of Embodiment 1, wherein the carbon fibers are continuous fibers, or wherein the carbon fibers are chopped fibers, or wherein the carbon fibers are woven, knitted, braided, or nonwoven, or wherein the carbon fibers comprise graphite, expanded graphite, graphene, a pyrolyzed carbon fiber, or a combination comprising at least one of the foregoing.

[0079] Embodiment 32. A sized carbon fiber composition comprising: a plurality of carbon fibers comprising a coating comprising a poly[2-(Co-6 alkyI)-2-oxazoline] sizing agent, preferably comprising a poly[2-(Ci_6 atkyl)-2-oxazoline] sizing agent, most preferably a poly [2- ethyi 2-oxazoline] sizing agent, in an amount of 0.01 to 1.2 wt%, based on the weight of the sized carbon fibers, wherein the sizing agent has a molecular weight of 1,000 to 800,000 g/mol, preferably 2,000 to 600,000 g/mol, or 3,000 to 120,000 g/mol, or 3,000 to 100,000 g/mol, or 4,000 to 60,000.

[0080] Embodiment 33. A method of manufacturing a polymer composite, the method comprising: contacting a sized carbon fiber composition comprising: a plurality of carbon fibers comprising a coating comprising a poly[2-(Co-6 alkyl)-2-oxazoline] sizing agent, preferably comprising a poly[2-(Ci-e alkyi)- 2 -oxazoline] sizing agent, most preferably a poly [2 -ethyl 2- oxazoiine] sizing agent, in an amount of 0.01 to 1.2 wt%, based on the weight of the sized carbon fibers, wherein the sizing agent has a molecular weight of 1,000 to 800,000 g/moi, preferably 2,000 to 600,000 g/mol, or 3,000 to 120,000 g/moi, or 3,000 to 100,000 g/mol, or 4,000 to 60,000, or a processed carbon fiber composition produced by the method of one or more of Embodi ents 15 to 18 with a thermoplastic polymer composition to provide the polymer composite.

[0081] Embodiment 34. The method of Embodiment 33, wherein contacting comprises contacting the sized or processed carbon fiber composition with a molten thermoplastic polymer composition, or wherein contacting comprises: contacting the sized or processed carbon fiber composition with a dry particulate thermoplastic polymer composition; and heating the contacted dry polymer powder to consolidate the particulate thermoplastic polymer composition, or wherein contacting comprises: contacting the sized or processed carbon fiber composition with a particulate polymer composition dispersed in an aqueous solvent; and consolidating the contacted fibers to provide the polymer composite.

[0082] Embodiment 35. A method of manufacturing a polymer composite, the method comprising: contacting the sized or processed carbon fiber composition of Embodiment 32 or Embodiment 19 with a thermoplastic polymer composition to provide the polymer composite. [0083] Embodiment 36. The method of Embodiment 35, wherein contacting comprises contacting the sized or processed carbon fiber composition with a molten thermoplastic polymer composition, wherein contacting comprises: contacting the sized or processed carbon fiber composition with a dry particulate thermoplastic polymer composition; and heating the contacted dry polymer powder to consolidate the particulate thermoplastic polymer composition, or wherein contacting comprises contacting the sized or processed carbon fiber composition with a particulate polymer composition dispersed in an aqueous solvent; and consolidating the contacted fibers to provide the polymer composite.

[0084] Embodiment 37. A method of manufacturing a polymer composite, the method comprising: contacting the sized or processed carbon fiber composition of Embodiment 32 or Embodiment 19 with a polymer precursor composition; and curing the contacted thermosetting polymer precursor composition to provide the polymer composite.

[0085] Embodiment 38. The method of Embodiment 37, wherein curing the polymer precursor composition on the sized or processed carbon fiber composition comprises heating the contacted fibers, or wherein contacting comprises contacting the sized or processed carbon fiber composition with a particulate polymer precursor composition dispersed in an aqueous solvent; and curing the contacted polymer precursor composition comprises heating the contacted fibers under conditions effective to cure and consolidate the particulate polymer precursor

composition.

[0086] Embodiment 39. The method of any one or more of Embodiments 35 to 38, wherein the sized or processed carbon fibers are present in an amount of 0.01 to 80 weight percent, preferably 0.1 to 60 weight percent, or 0.01 to 50 weight percent of the combined weight of the sized or processed carbon fibers and the polymer.

[0087] Embodiment 40. A polymer composite comprising: the sized or processed carbon fiber composition of Embodiment 32 or Embodiment 19; and a polymer.

[0088] Embodiment 41. The polymer composite of Embodiment 40, in the form of unidirectional tape comprising a thermoplastic polymer matrix.

[0089] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. "Combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms "a" and "an" and "the" herein do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. "Or" means "and/or". Reference throughout the specification to "one embodiment", "another embodiment", "an embodiment", and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments, in addition, it is to be understood that the described elements may be combined in any sui table manner in the various embodiments.

[0090] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

CLAIMS What is claimed is:

1. A method of manufacture of sized carbon fibers, the method comprising:

contacting a plurality of carbon fibers with a sizing composition to form coated carbon fibers, wherein the sizing composition comprises a polyoxazoline sizing agent, preferably a poly[2-ethyl 2-oxazoline] sizing agent, dissolved in a solvent; and

removing the solvent from the coated carbon fibers to form sized carbon fibers comprising the sizing agent in an amount of 0.01 to 1.2 weight percent based on the total weight of the sized carbon fibers, preferably 0.1 to 1.0 weight percent based on the total weight of the sized carbon fibers.

2. The method of claim 1 , wherein the contacting is by spraying the carbon fibers with the sizing composition, immersing the carbon fibers in the sizing composition, or drawing the carbon fibers through the sizing composition.

3. The method of claims 1 or 2, wherein the carbon fibers are continuous fibers, or wherein the carbon fibers are chopped fibers, or wherein the carbon fibers are woven, knitted, braided, or nonwoven, or wherein the carbon fibers comprise graphite, expanded graphite, graphene, a pyrolyzed carbon fiber, or a combination comprising at least one of the foregoing.

4. The method of any one or more of claims 1 to 3, wherein the sizing agent has a molecular weight of 1,000 to 800,000 g/mol, preferably 2,000 to 600,000 g/mol, or 3,000 to 120,000 g/mol, or 3,000 to 100,000 g/mol, or 4,000 to 60,000 g/mol.

5. The method of any one or more of claims 1 to 4, wherein the solvent is water, a protic polar organic solvent, an aprotic polar organic solvent, or a combination comprising at least one of the foregoing, preferably an aqueous solvent.

6. The method of any one or more claims 1 to 5, wherein the sizing composition comprises 1 to 40 weight percent, preferably 1 to 30 weight percent, or 1 to 20 weight percent, or 1 to 10 weight percent of the sizing agent.

7. The method of any one or more of claims 1 to 6, wherein the sizing composition further comprises a lubricant, a preservative, an antioxidant, a flame retardant, an antiseptic, a thixotropic agent, a titanate, a smoothing agent, a dispersing agent, a plasticizing agent, an antistatic agent, a dispersant, or a combination comprising at least one of the foregoing.

8. A sized carbon fiber composition comprising:

a plurality of carbon fibers comprising a coating comprising a polyoxazoline sizing agent, most preferably a poly[2-ethyl 2-oxazoline] sizing agent, in an amount of 0.01 to 1.2 wt , based on the weight of the sized carbon fibers, wherein the sizing agent has a molecular weight of 1,000 to 800,000 g/mol, preferably 2,000 to 600,000 g/mol, or 3,000 to 120,000 g/mol, or 3,000 to 100,000 g/mol, or 4,000 to 60,000.

9. A method of producing a processed carbon fiber composition, the method comprising: providing the sized carbon fiber composition of claim 8;

processing the sized carbon fiber composition; and

at least partially removing the sizing from the processed, sized carbon fiber composition to produce the processed carbon fiber composition.

10. The method of claim 9, wherein the processing comprises storing the carbon fibers, transporting the carbon fibers, heating the carbon fibers, shaping the carbon fibers, weaving the carbon fibers, knitting the carbon fibers, braiding the carbon fibers, stitching the carbon fibers, making a prepreg from the carbon fibers, packaging the carbon fibers, transporting the carbon fibers, or a combination comprising at least one of the foregoing.

11. The method of any one or more of claims 9 or 10, wherein removing comprises contacting the processed, sized carbon fiber composition with a solvent under conditions effective to remove the sizing from the carbon fibers.

12. The method of claim 11, wherein the solvent is water, and the contacting is at a temperature of 21 to 100°C, 40 to 90°C, preferably 50 to 70°C.

13. A processed carbon fiber composition produced by any one or more of the methods of claims 9 to 12.

14. A method of manufacturing a polymer composite, the method comprising:

contacting the sized or processed carbon fiber composition of claim 8 or 13 with a thermoplastic polymer composition to provide the polymer composite.

15. The method of claim 14, wherein contacting comprises contacting the sized or processed carbon fiber composition with a molten thermoplastic polymer composition, wherein contacting comprises:

contacting the sized or processed carbon fiber composition with a dry particulate thermoplastic polymer composition; and

heating the contacted dry polymer powder to consolidate the particulate thermoplastic polymer composition, or wherein contacting comprises

contacting the sized or processed carbon fiber composition with a particulate polymer composition dispersed in an aqueous solvent; and

consolidating the contacted fibers to provide the polymer composite.

16. A method of manufacturing a polymer composite, the method comprising:

contacting the sized or processed carbon fiber composition of claims 8 or 13 with a polymer precursor composition; and

curing the contacted thermosetting polymer precursor composition to provide the polymer composite.

17. The method of claim 16, wherein curing the polymer precursor composition on the sized or processed carbon fiber composition comprises heating the contacted fibers, or wherein contacting comprises

contacting the sized or processed carbon fiber composition with a particulate polymer precursor composition dispersed in an aqueous solvent; and

curing the contacted polymer precursor composition comprises heating the contacted fibers under conditions effective to cure and consolidate the particulate polymer precursor composition.

18. The method of any one or more of claims 14 to 17, wherein the sized or processed carbon fibers are present in an amount of 0.01 to 80 weight percent, preferably 0.1 to 60 weight percent, or 0.01 to 50 weight percent of the combined weight of the sized or processed carbon fibers and the polymer.

19. A polymer composite comprising:

the sized or processed carbon fiber composition of claims 8 or 13; and

a polymer.

20. The polymer composite of claim 19, in the form of unidirectional tape comprising a thermoplastic polymer matrix.