Patent Description:
The present disclosure relates generally to electrically conductive sized fiber including a fiber and a sizing composition adhered to a surface of the fiber, wherein the sizing composition includes at least one sizing compound and a plurality of graphene oxide nanoparticles. The present disclosure also relates generally to fiber-reinforced resin composite including electrically conductive sized fibers, articles including fiber-reinforced resin composites and methods of making such electrically conductive sized fibers.

In general, the fiber-reinforced resin composites display good longitudinal electrical conductivity, but poor through-thickness transverse electrical conductivity. Hence, there is a need for an improved fiber-reinforced resin composite with improved through-thickness transverse electrical conductivity.

In an aspect, there is an electrically conductive sized fiber according to claim <NUM>.

In another aspect, there is a method comprising the steps of:.

In yet another aspect, there is a fiber-reinforced resin composite comprising:.

In yet another aspect, there is an article comprising at least two components adhesively bonded to each other, wherein at least one of the at least two components comprises the fiber-reinforced resin composite, as disclosed hereinabove,.

In another aspect, there is a spar cap comprising a fiber-reinforced resin composite comprising:.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one (several) embodiment(s) of the invention, and together with the written description, serve to explain certain principles of the invention.

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

The wind energy industry requires lightning protection for the blades in which carbon fiber-reinforced resin composites have been commonly used for the spar caps. Due to the strong anisotropy of the electrical conductivity of the carbon fibers and uni-directional planar tow form of these carbon fiber-reinforced resin composites, the lengthwise conductivity of these carbon fiber-reinforced resin composites can be four orders of magnitude higher than transverse conductivity. Hence, as a result of this anisotropy, when a lightning strike, the high energy electricity would flow lengthwise, but would arc transversely, which could result in elevation in temperature, and thereby can cause delamination or incineration of the spar cap. Therefore, it has been discovered that there is a need to effectively enhance the through-thickness transverse electrical conductivity of the carbon fiber-reinforced resin composites forming the spar cap. It has been contemplated to increase the electrical conductivity of materials by various techniques, such as:.

To the extent that these approaches have various issues, alternative approaches may be more efficient and cost effective for enhancing the electrical conductivity of the carbon fiber-reinforced resin composite.

Disclosed herein is an electrically conductive sized fiber, a fiber-reinforced resin composite, articles including such electrically conductive sized fiber and fiber-reinforced resin composite and methods of making thereof.

In an aspect, there is an electrically conductive sized fiber including a fiber and a sizing composition adhered to a surface of the fiber. In such an embodiment, the sizing composition can include at least one sizing compound and a plurality of graphene oxide nanoparticles. In an embodiment, the sizing composition is substantially free of graphene nanoparticles.

As used herein, the term substantially free of graphene nanoparticles means that the graphene nanoparticles are not added to the sizing composition, but may be present as an impurity in a minor amount along with graphene oxide nanoparticles.

As used herein, the term "graphene oxide" refers to an oxidized derivative of graphene, with a resultant hydrophilic nature and colloidal stability in aqueous media. Furthermore, as used herein, the term "graphene oxide" does not include graphene, graphyne and graphone.

Graphyne is a two-dimensional carbon allotrope of graphene with honeycomb structure and directional electronic properties. Graphone is a hydrogenated derivative of graphene and is more useful for nanoelectronics and spintronics. Graphene composition is largely dependent upon the purity of the graphite from which it was produced, as it is, by definition (Webster) "an extremely electrically conductive form of elemental carbon that is composed of a single flat sheet of carbon atoms arranged in a repeating hexagonal lattice" - so although the intent is pure carbon (C), but impurities such as oxygen (O) may be present. Thus, while graphyne, graphone and graphene are hydrophobic, graphene oxide is hydrophilic in nature.

The graphene oxide (GO) is typically produced directly from graphite through the use of strong oxidizing agents and concentrated acids using Hummer's Method (<NPL>). The typical graphene oxide (GO) from Hummer's Method contains a variety of functional groups attached to the hexagonal carbon sheet, including carboxylic groups (O-C=O), carbonyls (C=O), epoxides (C-O-C), hydroxyls (C-OH), and others. For example, the GO can be produced by a wet-milling process, resulting in an edge-functionalized version with carboxylic (O-C-O) and hydroxyl (C-OH) functionalities.

A composition of an exemplary graphene oxide available from Graphen-AD has <NUM>% carbon, <NUM>% oxygen, <NUM>% sulfur, <NUM>% hydrogen and <NUM>% nitrogen and another exemplary composition of graphene oxide available from Garmor has <NUM>-<NUM>% carbon and corresponding <NUM>-<NUM>% oxygen, without the other impurities.

In an embodiment, the graphene oxide nanoparticles are in the form of graphene oxide nanoplatelets (GONP). In another embodiment, the graphene oxide nanoparticles are edge oxidized graphene oxide nanoplatelets (GONP), as shown in <FIG>. The graphene oxide nanoplatelets can have a particle size distribution in the range of <NUM> to <NUM> or <NUM> to <NUM> with an average size in the range of <NUM> to <NUM> and thickness in less than <NUM>. The graphene oxide nanoplatelets have an average aspect ratio in the range of <NUM>-<NUM>.

The sizing composition may include graphene oxide nanoparticles in an amount in the range of <NUM>-<NUM>%, or preferably <NUM>-<NUM>%, or more preferably <NUM>-<NUM>% by weight, based on the total solid content of the sizing composition. In an embodiment, graphene oxide may be present in the sizing composition in an amount of at least, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% by weight and at most of <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% by weight, based on the total solid content of the sizing composition. As used herein, the term "solid content of the sizing composition" refers to the total amount of plurality of graphene oxide nanoparticles and at least one sizing compound.

The sizing composition may include at least one sizing compound from among film formers, coupling agents, and processing aids. The film formers play a vital role in protecting the fibers from abrasion and may be present in an amount in the range of <NUM>-<NUM>%. , or <NUM>-<NUM>%, or <NUM>-<NUM>% by weight, based on the total solid content of the sizing composition. Suitable examples of film formers include, but are not limited to polyvinyl acetate, epoxy, polyester, polyurethane, etc. Suitable examples of coupling agents include, but are not limited to, chromium (III) methacrylate (available as Volan® from Zacion LLC), chromium (III) methacrylate, silanes, titanates, etc. Suitable examples of processing aids include, but are not limited to, lubricants, wetting agents, neutralizing agents, antistatic agents, antioxidants, nucleating agents, crosslinkers, and any combination thereof.

<CIT> discloses in §<NUM>-<NUM> <FIG> an electrically conductive sized fiber comprising a fibre (carbon fiber <NUM>), and a sizing composition adhered to a surface of the fiber, wherein the sizing composition comprises at least one sizing compound (matrix material <NUM>) and a plurality of graphene oxide nanoparticles (<NUM> GNP).

In an embodiment, the sizing composition further includes an aqueous solvent, such that the at least one sizing compound and a plurality of graphene oxide nanoparticles are dispersed in the aqueous solvent, thereby forming an aqueous dispersion. The aqueous solvent may be present in an amount in the range of <NUM>-<NUM>%, or <NUM>-<NUM>%, or <NUM>-<NUM>% by weight based on the total weight of the sizing composition.

In another embodiment, the sizing compositions of the present invention have a long, useful shelf life, as compared to most aqueous dispersions, which have very limited shelf lives. <FIG> shows a picture of a sizing composition comprising at least one sizing compound and a plurality of graphene oxide nanoparticles, being stable after standing over a period of <NUM> week. In an embodiment of the present invention, the sizing composition can be non-hazardous and imposes no environmental effect when disposed of as compared to most aqueous dispersions, the disposal of which incurs expensive disposal fees.

The electrically conductive sized fiber can include any suitable fiber, including, but not limited to, carbon fibers. In an embodiment of the electrically conductive sized fiber of the present invention, the fiber is a polyacrylonitrile (PAN)-based carbon fiber. The electrically conductive fiber can be in any suitable form including, but not limited to, a dry tow, a fabric, a felt, a scrim, a prepreg with thermoplastic or thermosetting resin, a pultruded plate, or a sheet molding compound. In an embodiment, the electrically conductive sized fiber has a sizing composition in an amount (also referred to as sizing level) in the range of <NUM>-<NUM>%, <NUM>-<NUM>%, or <NUM>-<NUM>%, by weight, based on the total amount of fiber and sizing composition after drying.

In an embodiment, the carbon fibers have an electrical resistivity of about <NUM> Ohm-cm. The carbon fibers can have an average diameter in the range of <NUM>-<NUM> microns, and any suitable length. In an embodiment, milled carbon fibers can have an average diameter of <NUM> microns.

The carbon fiber can have any suitable tow bundle size, including, but not limited to, at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>,.

Suitable examples of commercially available carbon fibers include, but are not limited to: PX35 available from Zoltek, TORAYCA® T700 and T800, all available from Toray, SIGRAFIL available from SGL, Grafil available from Mitsubishi, AKSAKA available from DowAksa, Tenax available from Toho.

In an aspect, there is a method for manufacturing an electrically conductive sized fiber; the electrically conductive sized fiber comprising a fiber and a sizing composition adhered to a surface of the fiber, wherein the sizing composition includes at least one sizing compound and a plurality of graphene oxide nanoparticles.

<FIG> shows an exemplary method comprising the step of first providing a sizing composition comprising at least one sizing compound and plurality of graphene oxide nanoparticles, followed by coating a sized or an un-sized fiber tow with the sizing composition by drawing the un-sized fiber tow through a sizing bath containing the sizing composition such that the un-sized fiber tow is immersed in the sizing composition. The sizing composition contained in the sizing bath can include at least one sizing compound and a plurality of graphene oxide nanoparticles. As shown in <FIG>, the method can further include the step of drying the coated fiber tow to form an electrically conductive sized fiber including the fiber and the sizing composition adhered to a surface of the fiber, the sizing composition includes the at least one sizing compound and the plurality of graphene oxide nanoparticles. The step of drying can be carried out at a temperature in the range of <NUM>-<NUM>, or <NUM>-<NUM>, or <NUM>-<NUM> for an amount of time in the range of <NUM>-<NUM> minutes, or <NUM>-<NUM> minutes, or <NUM>-<NUM> minutes, in air, inert atmosphere like nitrogen, argon, etc, or under vacuum. In an embodiment, the drying step can be carried out in a forced air, multi-zone, such as a <NUM>-zone continuous oven. In another embodiment, the drying step can be carried out at for example around <NUM> for about <NUM> minutes in forced air / <NUM>-zone continuous oven. The method also includes a step of spooling the electrically conductive sized fiber.

In an embodiment, the step of providing a sizing composition comprises adding a plurality of graphene oxide nanoparticles in solid form to at least one sizing compound. In another embodiment, the step of providing a sizing composition comprises adding an aqueous dispersion of the plurality of graphene oxide nanoparticles to at least one sizing compound. In yet another embodiment, the method may further include re-dispersing graphene oxide nanoparticles in the aqueous dispersion by any suitable mechanical means, such as sonication including horn sonication or bath sonication, and high speed shear mixing, before the step of adding the graphene oxide dispersion to the sizing composition, as shown in <FIG>. The amount of time required for re-dispersing graphene oxide nanoparticles will depend upon the graphene oxide composition and the mechanical means and can be in the range of <NUM> seconds to <NUM> minutes, or preferably <NUM> to <NUM> minutes.

In an aspect, the method further comprises forming a fiber-reinforced resin composite in the form of a pultruded sheet or a resin-infused fabric, or a preimpregnated tape (prepreg, impregnated with a thermoplastic resin or a thermosetting resin), or a sheet molding compound (SMC). In an embodiment, the step of forming a fiber-reinforced resin composite can include arranging the electrically conductive sized fiber into a fabric and infusing the fabric with a binder resin to form a resin infused fabric or a prepreg. In another embodiment, the step of forming a fiber-reinforced resin composite can include arranging the electrically conductive sized fiber into a planar tow form, infusing the planar tow form with a binder resin and pultruding the resin infused planar tow form to form a pultruded sheet,.

In another embodiment, the step of forming a fiber-reinforced resin composite can include arranging a combination of electrically conductive sized fiber and fabric made with electrically conductive sized fiber into a structural cross section form, infusing the structural cross section form with a binder resin and pultruding the resin infused section form to result in a pultruded structural section (for example a C-section, J-section, or Pi-section). <FIG> shows a picture of an exemplary C-section, in accordance with various embodiments of the present invention.

In another embodiment, the step of forming a fiber-reinforced resin composite can include compounding at least one of a plurality of chopped or a plurality of continuous electrically conductive sized fibers with a binder resin and compression molding or injection molding the resulting composition into an article.

In another aspect, the method can further include forming an article by adhesively bonding at least two components to each other. In such an embodiment, at least one of the at least two components can include the fiber-reinforced resin composite, as disclosed hereinabove.

In an embodiment, the electrically conductive sized fiber of the present invention is suitable for use in wind blade applications.

In an aspect, there is a fiber-reinforced resin composite including the electrically conductive sized fiber, as disclosed hereinabove and a binder resin.

In an embodiment of the fiber-reinforced resin composite, the fiber is a carbon fiber.

The fiber-reinforced resin composites according to the present invention may be formed from and based on any binder resin known in the art.

Non-limiting examples of a binder resin that is a thermoset (co)polymer includes unsaturated polyesters, epoxy resins, vinyl ester resins, phenolic resins, thermoset polyurethanes, polyimides, bismaleimide resins, benzoxazine resins, and silicone resins.

Non-limiting examples of a binder resin that is a thermoplastic (co)polymer includes, polyolefins, cyclic polyolefins, acrylonitrile butadiene styrene, polyvinyl chloride, polystyrene, thermoplastic polyesters, polyvinyl alcohols, polymethyl methacrylates, styrene maleic anhydrides, polyoxymethylene (acetals), thermoplastic polyurethanes, polyethylene terephthalates, polytrimethylene terephthalates, polybutylene terephthalates, polyamides, polycarbonates, polyvinylpyrrolidone, polytetrafluoroethylene, polysulfones, polyethersulfones, polyphenylene sulfides, polyetherimides, polyamide-imides, polyetheretherketones, and polyaryletherketones, including alloys and blends.

In an embodiment, the fiber-reinforced resin composite is in the form of a pultruded sheet, a fabric, or a prepreg. In another embodiment, the fiber-reinforced resin composite in the form of a pultruded sheet incudes carbon fibers in a planar tow form fused with the binder resin. In yet another embodiment, the fiber-reinforced resin composite in the form of a fabric includes a multidirectional fabric, a uni directional fabric or a woven fabric.

In an embodiment, the fiber-reinforced resin composite includes at least one of <NUM>-<NUM>% by volume of electrically conductive sized carbon fiber reinforcement and a vinyl ester resin, <NUM>-<NUM>% by volume of electrically conductive sized fiber reinforcement and a polyester resin or <NUM>-<NUM>% by volume of electrically conductive sized carbon fiber reinforcement and an epoxy resin, where the amount in % by volume is based on the total volume of the fiber-reinforced resin composite. In an embodiment, the fiber-reinforced resin composite is in the form of a pultruded sheet, a resin-infused fabric, a pre-impregnated tape, or a sheet molding compound. In the pultruded form, the electrically conductive sized fiber may be present in an amount in the range of <NUM>-<NUM>%, or preferably <NUM>-<NUM>%, by volume, based on the total volume of the fiber-reinforced resin composite. In the pultruded form, the electrically conductive sized fiber may be present in an amount in the range of <NUM>-<NUM>%, or preferably <NUM>-<NUM>%, by volume, based on the total volume of the fiber-reinforced resin composite. In the prepreg form, the electrically conductive sized fiber may be present in an amount in the range of <NUM>-<NUM>%, or preferably <NUM>-<NUM>%, by volume, based on the total volume of the fiber-reinforced resin composite. In the resin-infused fabric form, the electrically conductive sized fiber may be present in an amount in the range of <NUM>-<NUM>%, or preferably <NUM>-<NUM>%, by volume, based on the total volume of the fiber-reinforced resin composite.

In an embodiment, the fiber-reinforced resin composite in the form of a pre-impregnated tape comprises a preimpregnated unidirectional sheet of fibers or a preimpregnated fabric, where the fabric is one or more of a multidirectional fabric, a unidirectional fabric or a woven fabric.

In an embodiment, the fiber-reinforced resin composite in the form of a sheet molding compound comprises plurality of continuous or discontinuous carbon fibers, a multidirectional fabric, a unidirectional fabric, a woven fabric, or a non-woven fabric, combined with a binder resin.

The fiber-reinforced resin composite may also include any filler and/or particle, known in the art for reinforcing composites, such as polymer composites. Examples of such particles include, but are not limited to, talc, calcium carbonate, aluminum hydroxide, titanium oxides, and silica.

In another aspect, there is an article comprising at least two components adhesively bonded to each other, where at least one of the at least two components includes the fiber-reinforced resin composite, as disclosed hereinabove, including the electrically conductive sized fiber of the present disclosure.

<FIG> shows a sectional view of a portion of an exemplary article comprising a composite panel, in accordance with various embodiments of the present invention. The exemplary composite panel includes two components, a first component adhesively bonded to a second component, where at least one of the first component or the second component includes the electrically conductive sized fiber reinforcement of the present disclosure and a binder,.

<FIG> shows a sectional view of a portion of another exemplary article comprising a composite panel comprising a plurality of panels adhesively bonded to each other, such that at least one of the plurality of panels includes the electrically conductive sized fiber of the present disclosure. As shown in <FIG>, the exemplary composite panel comprises at least four panels, a first panel is adhesively bonded to a second panel, the second panel adhesively bonded to a third panel and the third panel adhesively bonded to a fourth panel. In an embodiment, the panels are stacked on top of each other such that at least one edge is slanted and has a slope.

The composite panels of the present invention can have any suitable thickness, such as in the range of <NUM>-<NUM>.

In an embodiment, the article is a spar cap including a fiber-reinforced resin composite and configured to distribute high energy electricity and reduce arcing or delamination when exposed to the high energy electricity. The spar cap includes the fiber-reinforced resin composite, as disclosed hereinabove, including, an electrically conductive sized fiber reinforcement and a binder resin. <FIG> shows a schematic sectional diagram of a portion of a spar cap.

In an embodiment of the spar cap, the fiber-reinforced resin composite comprises <NUM>-<NUM>% by volume of electrically conductive sized carbon fibers fused and a binder resin, wherein the amount in % by volume is based on the total volume of the fiber-reinforced resin composite. In an embodiment, the fiber-reinforced resin composite sheet includes <NUM>-<NUM>% by volume of electrically conductive sized carbon fibers fused with a vinyl ester resin. In another embodiment, the fiber-reinforced resin composite sheet includes <NUM>-<NUM>% by volume of electrically conductive sized carbon fibers fused with an epoxy resin. In yet another embodiment, the fiber-reinforced resin composite sheet includes <NUM>-<NUM>% by volume of electrically conductive sized fiber reinforcement fused with a polyester resin. In yet another embodiment, the fiber-reinforced resin composite sheet in the spar cap is a pultruded sheet comprising <NUM>-<NUM>%, or preferably <NUM>-<NUM>%, by volume of electrically conductive sized fiber, based on the total volume of the fiber-reinforced resin composite.

It is believed that the inclusion of the graphene oxide nanoparticles in the electrically conductive sized fiber substantially enhances the electrical conductivity of the fiber-reinforced resin composite in the transvers direction. The resulting spar cap of the present invention will be far more lightning resistant in comparison to one without electrically conductive graphene oxide nanoparticles into the sizing of the fiber.

The introducing of electrically conductive graphene oxide nanoparticles into the sizing of the fiber, in accordance with the present invention provides several advantages:.

ZOLTEK PX-<NUM> carbon fiber bundle (having carbon size diameter of ~<NUM> in diameter) were obtained from Zoltek Corporation. Edge-Oxidized Graphene Oxide (EOGO), graphene oxide nanoplatelets (with carboxylic and hydroxyl groups) available as <NUM> weight% dispersion in water were obtained Garmor, Inc. (Orlando, FL). EOGO used herein had a composition of <NUM>-<NUM>% carbon and corresponding <NUM>-<NUM>% oxygen present in the form of carboxy! groups and hydroxyl groups, without the other impurities, and was produced by wet milling process. The graphene oxide nanoplatelets were used as is except the dispersion was sonicated before use to redisperse graphene oxide nanoparticles in water.

For the sizing, % solids was determined by moisture balance @ <NUM> until there was no change in weight.

For the fiber, % moisture was determined by weighing before and after heating at <NUM> hours in oven @ <NUM>; % size content was determined by weighing before and after solvent extraction; tow mass (g/m) was based on weight of <NUM> long sample; and fuzz (ppm) was determined by dragging the fiber across a rough surface and weighing before and after,.

Electrical conductivity was measured on a composite plate made of conductively sized carbon fiber and a thermoset resin with a PROSTAT PRS-<NUM> resistance system set. Measurement methods followed the industry standard tests ANSI/ESD STM11. <NUM> to measure surface resistance, and ANSI/ESD STM11. <NUM> to measure volume resistance.

<FIG> shows an overall process of making an electrically conductive sized fiber. The process included the following steps:.

The graphene oxide dispersion was re-sonicated for <NUM> minutes before adding to a general purpose epoxy-compatible sizing composition including at least one sizing compound. Then, the un-sized carbon fiber bundle (called a tow) was run through a bath of sizing which contained typical sizing compounds used for carbon fibers plus the inclusion of Graphene-oxide (GO) nano-platelets. Standard conditions, as would be used for sizing composition with graphene oxide nanoplatelets, but the amount of sizing deposited on the fiber was controlled through adjustment of the sizing concentration in the bath. The wetted, sized tow was then pulled through a set of nip rolls set at 50psi to reduce the moisture content to a target of <NUM>%. The wetted, sized fiber tow was then dried at <NUM> for <NUM> minutes under air and wrapped up on a spool.

The sizing composition with graphene oxide was found to be stable with solids constant over weekend and even one-week old sample appeared relatively stable, as shown in <FIG>. Some graphene oxide nanoparticles were found to settle to the bottom immediately, probably due to lack of functionalization.

Claim 1:
An electrically conductive sized fiber comprising:
a carbon fiber, and
a sizing composition adhered to a surface of the fiber, wherein the sizing composition comprises at least one sizing compound and a plurality of graphene oxide nanoparticles,
wherein the graphene oxide nanoparticles are in the form of graphene oxide nanoplatelets, and
wherein the graphene oxide nanoparticles are encapsulated by the at least one sizing compound and adhered to the surface of the fiber.