Brief description of the drawings

Various aspects of the present general inventive concept will be more readily understood from the following description of certain exemplary embodiments, which is provided below and shown in the accompanying drawings.

Fig. 1 shows the results of the "drape test" performed on various reinforcing fibers.

Fig. 2 illustrates the range of stiffness achieved by the surface treated carbon fibers (tape and multi-start roving) compared to an otherwise identical untreated carbon fiber tape.

Fig. 3 illustrates the range of stiffness achieved for a surface treated multi-start fiber glass roving compared to an otherwise identical untreated multi-start fiber glass roving.

Brief description of the drawings

Various aspects of the present general inventive concept will be more readily understood from the following description of certain exemplary embodiments, which is provided below and shown in the accompanying drawings.

Fig. 1 shows the results of the "drape test" performed on various reinforcing fibers.

Fig. 2 illustrates the range of stiffness achieved by the surface treated carbon fibers (tape and multi-start roving) compared to an otherwise identical untreated carbon fiber tape.

Fig. 3 illustrates the range of stiffness achieved for a surface treated multi-start fiber glass roving compared to an otherwise identical untreated multi-start fiber glass roving.

Detailed description of the invention

While the present general inventive concept may be susceptible to embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an exemplary general inventive concept. Therefore, the present general inventive concept is not intended to be limited to the specific embodiments shown herein.

Unless otherwise defined, terms used herein have the same meaning as commonly understood by one of ordinary skill in the art around the general inventive concept. The terminology used herein is for the purpose of describing exemplary embodiments of the general inventive concept only and is not intended to be limiting of the general inventive concept. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "about" means within +/-10% of the value, or more preferably within +/-5% of the value, and most preferably within +/-1% of the value.

As used herein, the term "wetting" refers to the ability of a resin to bind to the surface of a fiber and to spread out and bind to the surface of the fiber uniformly. Wetting is caused by intermolecular interactions between the liquid and the solid surface.

As used herein, the term "tow" refers to a large collection of filaments, typically formed simultaneously and optionally coated with a sizing composition. Tows are named by the number of filaments they contain. For example, a 12k tow contains about 12,000 filaments.

As used herein, the term "roving" refers to a collection of parallel strands (assembled roving) or parallel continuous filaments (direct roving) that are not intentionally twisted. Rovings include single end rovings and multiple end rovings ("MERs"). Single end rovings refer to a single bundle of fibers that bind continuous filaments into discrete strands. A multi-start roving is made up of a plurality of discrete strands, each strand having a plurality of continuous filaments. The term "continuous" as used herein in connection with a filament, strand or roving means that the filament, strand or roving typically has a significant length, but it is not to be understood that the length is infinite or infinite.

The present invention relates to a method of imparting increased, adjustable stiffness to reinforcing fibers, such as carbon fibers. The reinforcing fibers may include any type of fiber suitable to provide the resulting composite with the desired structural qualities and, in some cases, also enhance thermal properties. Such reinforcing fibers may be organic, inorganic or natural fibers. In some exemplary embodiments, the reinforcing fibers are made of any one or more of glass, carbon, aramid, polyester, polyolefin, polyamide, silicon carbide (SiC), boron nitride, and the like. In some exemplary embodiments, the reinforcing fibers comprise one or more of glass, carbon, and aramid fibers. In some exemplary embodiments, the reinforcing fibers are carbon fibers. It should be understood that although the present application generally refers to reinforcing fibers as carbon fibers, the reinforcing fibers are not so limited and may alternatively or additionally include any reinforcing fibers described herein or known in the art (now or in the future).

Carbon fibers are generally hydrophobic, electrically conductive fibers that have high stiffness, high tensile strength, high temperature resistance, and low thermal expansion, and are generally lightweight, making them popular in forming reinforced composites. However, carbon fibers can cause processing difficulties, resulting in slower and more costly product manufacturing. For example, conventional carbon fibers often sag and bend due to gravity when held parallel to the ground. Due to the lack of stiffness, the fibers are difficult to chop and use in downstream manufacturing processes. Further problems include the tendency of the fibers to break and/or fray during the rubbing, drawing and stretching movements that occur during processing. Such breakage and abrasion can result in the release of particles into the atmosphere and the formation of "fuzz" on the fibers. In addition to processing difficulties, carbon fibers are hydrophobic and tend to agglomerate, making them more difficult to wet than hydrophilic glass fibers in conventional matrices.

The carbon fibers may be turbostratic or graphitic carbon fibers, or have a mixed structure in which turbostratic and graphitic portions are present together, depending on the precursor used to make the fibers. In turbostratic carbon fibers, sheets of carbon atoms are randomly folded or crimped together. Carbon fibers derived from Polyacrylonitrile (PAN) are turbostratic elastomers, while carbon fibers derived from mesophase pitch are graphitic carbon fibers after heat treatment at temperatures in excess of 2200 ℃. In some exemplary embodiments, the carbon fibers of the present invention are derived from PAN.

In some exemplary embodiments, the reinforcing fibers of the present invention are coated with a sizing composition to protect the fibers, improve mechanical properties, and/or promote thermal and hydrolytic stability during processing. The sizing composition may also form surface functional groups to promote improved chemical bonding and uniform mixing within the polymer matrix. The uniform mixing of fibers or "wetting" within the polymer matrix material is a measure of how well the reinforcement material is encapsulated by the polymer matrix. It is desirable to have the reinforcing fibers completely wet and free of dry fibers. Incomplete wetting during this initial processing can negatively impact subsequent processing and the surface characteristics of the final composite.

At any time during the fiber forming process (e.g., prior to packaging or storing the formed fibers), the sizing composition may be applied to the reinforcing fibers in an amount of from about 0.5% to about 5% by weight of fiber solids, or from about 1.0% to about 2.0% by weight of fiber solids. Alternatively, the fibers can be coated with the sizing composition after the fibers are formed (e.g., after the fibers are packaged or stored). In some exemplary embodiments, the sizing composition is an aqueous-based composition, such as a suspension or emulsion. The sizing composition may include at least one film forming agent. The film former holds the individual filaments together to aid in forming the fiber and to protect the filaments from damage due to abrasion, including, but not limited to, interfilament abrasion. Acceptable film forming agents include, for example, polyvinyl acetate, polyurethane, modified polyolefin, polyester, epoxy, and mixtures thereof. The film former also assists in improving the bonding characteristics of the reinforcing fibers to various resin systems. In some exemplary embodiments, the sizing composition aids in the compatibilization of the reinforcing fibers with epoxy, polyurethane, polyester, nylon, phenolic, and/or vinyl ester resins.

In particular for carbon fibres, these fibres are usually supplied in the form of a continuous tow wound on a reel. Each carbon filament within the tow is a continuous cylinder having a diameter of about 5 μm to about 10 μm. Carbon tows have a wide variety of sizes, from 1k, 3k, 6k, 12k, 24k, 50k to more than 50k, etc. The K value represents the number of individual carbon filaments within the tow. For example, a 12k tow consists of about 12,000 carbon filaments, while a 50k tow consists of about 50,000 carbon filaments.

To obtain a fine tow (e.g., 12k or less), the carbon must be made into a fine carbon tow, or a larger carbon tow must be split to reduce its filament count. Splitting high carbon fiber bundles (e.g., 24k, 50k, or greater) into smaller splits (e.g., less than 12k) helps provide better resin impregnation and better dispersion when processing the fiber bundles.

In some exemplary embodiments, a carbon fiber tow may be spread to separate individual carbon filaments and begin to produce a plurality of thinner fiber bundles. The spread carbon fibers are then pulled under tension to maintain consistent spreading and further increase spreading between fibers. For example, a plurality of carbon fibers having a width of about 3/8 "to about 1/2 may be pulled under tension along various rollers to form about 3/4" to about 1¹/₂"spreading. The angle and radius of the rolls should be set to maintain a tension that is not too high, which can pull the spread fibers back together.

It has been found that surface treating the reinforcing fibers at any time during the formation or processing of the reinforcing fibers can increase the stiffness of the fibers and improve their processability. The surface treatment may be performed when forming the reinforcing fibers (e.g., when PAN is converted to carbon fibers). Alternatively or additionally, the surface treatment may be performed after sizing the reinforcing fibers with the sizing composition and at least partially curing. Alternatively, additionally, the surface treatment may be performed after the reinforcing fibers are further treated, for example after the carbon fibers are spread and/or separated into smaller fiber bundles.

As used herein, the surface treatment may take a variety of forms, such as a coating composition. Exemplary coating compositions are disclosed in PCT/US16/55936, the disclosure of which is incorporated herein by reference in its entirety. The surface treatment may further comprise a heat treatment for promoting cross-linking of the previously applied chemical species present on the fibers from the sizing composition. In some exemplary embodiments, the heat treatment is performed by passing the fibers over heated rollers or by using heated air (e.g., an oven). In some exemplary embodiments, the surface treatment comprises exposing the fibers previously coated with the sizing composition to a high humidity environment whereby the chemicals present on the fibers form crosslinks by the addition of moisture. In other exemplary embodiments, the surface treatment may include a physical treatment and/or a plasma treatment.

In some exemplary embodiments, the surface treatment is an aqueous coating composition comprising from about 2.5% to about 5.0% by weight solids, or from about 3.0% to about 4.5% by weight solids, or from about 3.5% to about 4.0% by weight solids, based on the total solids content of the aqueous composition. Once applied to the fibers, the coating composition has a solids content of from about 0.1% to about 5.0% by weight, or an amount of active strand solids of from about 0.5% to about 2.0% by weight, or an amount of active strand solids of from about 0.5% to about 1.0% by weight.

In some exemplary embodiments, the aqueous coating composition includes at least one film former. For example, the coating composition may include one or more of polyvinylpyrrolidone (PVP), polyvinyl acetate (PVA), and Polyurethane (PU) and epoxy resin as film formers.

Polyvinylpyrrolidone exists in several molecular weight grades characterized by a K-value. For example, and in no way limiting, PVP K-12 has a molecular weight of about 4,000 to about 6,000; PVP K-15 has a molecular weight of about 6,000 to about 15,000; PVP K-30 has a molecular weight of about 40,000 to about 80,000; and PVP K-90 has a molecular weight of about 1,000,000 to about 1,700,000. In some exemplary embodiments, the film former comprises PVP K-90.

The film former is present in the coating composition in an amount of about 0.5 wt% to about 5.0 wt%, or about 1.0 wt% to about 4.75 wt%, or about 3.0 wt% to about 4.0 wt%, based on the total solids content of the aqueous composition. Once applied to the fiber strands, the film former may be present in an amount of about 0.1 to about 2.0 weight percent strand solids, or about 0.3 to about 0.6 weight percent strand solids.

In some exemplary embodiments, the coating composition additionally includes a compatibilizer. Compatibilizers may cooperate to provide various functions between the film former, reinforcing (e.g., carbon) fiber, and resin interface. In some exemplary embodiments, the compatibilizer includes a coupling agent such as a silicone-based coupling agent (e.g., a silane coupling agent), a titanate coupling agent, or a zirconate coupling agent. Silane coupling agents are conventionally used in sizing compositions for inorganic substrates having hydroxyl groups that are reactive with silanol-containing reactive groups. Although such coupling agents are conventionally used in sizing compositions for glass fibers, alkali metal oxides and carbonates cannot form stable bonds with Si-O. However, it has been surprisingly found that the use of such coupling agents in the surface treatment of the present invention does in fact serve to provide adhesion of the film-forming polymer to the non-glass (i.e., carbon) fibers and reduce the level of fuzzing or broken fiber filaments during subsequent processing and separation. Examples of silane coupling agents that may be suitable for use in the coating composition include those characterized by the functional groups acryloyl, alkyl, amino, epoxy, vinyl, azido, ureido, and isocyanate groups.

Suitable silane coupling agents for use in the coating composition include, but are not limited to, gamma-aminopropyltriethoxysilane (A-1100), n-trimethoxy-silyl-propyl-ethylenediamine (A-1120), gamma-methacryloxypropyltrimethoxysilane (A-174), gamma-glycidoxypropyltrimethoxysilane (A-187), methyl-trichlorosilane (A-154), methyl-trimethoxysilane (A-163), gamma-mercaptopropyl-trimethoxysilane (A-189), bis- (3- [ triethoxysilyl ] propyl) tetrasulfane (A-1289), gamma-chloropropyl-trimethoxysilane (A-143), vinyl-triethoxysilane (A-151), Vinyl-tris- (2-methoxyethoxy) silane (A-172), vinylmethyldimethoxysilane (A-2171), vinyl-triacetoxysilane (A-188), octyltriethoxysilane (A-137), methyltriethoxysilane (A-162), polyazamidosilane (A-1387), and gamma-ureidopropyltrialkoxysilane (A-1160).

In some exemplary embodiments, the compatibilizer comprises a mixture of two or more silane coupling agents. For example, the compatibilizer may include a mixture of: aminopropyltriethoxysilane (A-1100) and one or more of methyl-trimethoxysilane (A-163) and gamma-methacryloxypropyltrimethoxysilane (A-174). In some exemplary embodiments, the compatibilizer includes one or more of polyazamidosilane (A-1387) and gamma-ureidopropyltrialkoxysilane (A-1160).

In some cases, the compatibilizer includes a ratio of about 1: 1 to about 3: 1 a-1100 and a-163. In some cases, the compatibilizer is blended at a ratio of about 1: 1 to about 3: a ratio of 1 includes A-1100 and A-174.

In some exemplary embodiments, the compatibilizer includes an organic dialdehyde. Exemplary dialdehydes include glutaraldehyde, glyoxal, malondialdehyde, succindialdehyde, phthalaldehyde, and the like. In some exemplary embodiments, the organic dialdehyde is glutaraldehyde.

In some exemplary embodiments, the compatibilizer includes one or more antistatic agents, such as quaternary ammonium antistatic agents. The quaternary ammonium salt antistatic agent may include triethylammonium alkyl ether sulfate, which is a trialkyl alkyl ether ammonium salt having a trialkyl group, an alkyl ether group having 1 to 3 carbon atoms, and an ether group of ethylene oxide or propylene oxide, and/or an alkyl ether group having 4 to 18 carbon atoms. An example of ammonium triethylalkylether sulfate is EMERSTAT 6660A.

The compatibilizer may be present in the coating composition in an amount of about 0.05 wt% to about 5.0 wt% active solids, or in an amount of about 0.1 wt% to about 1.0 wt% active solids, or in an amount of about 0.2 wt% to about 0.7 wt% active solids. In some exemplary embodiments, the compatibilizer is present in the coating composition in an amount of about 0.3 to about 0.6 percent by weight active solids.

In some exemplary embodiments, the coating composition has a pH of less than about 10. In some exemplary embodiments, the pH of the coating composition is from about 3 to about 7, or from about 4 to about 6, or from about 4.5 to about 5.5.

Excess coating composition remaining on the fibers can be removed to at least partially dry the fibers. The fibers may be dried by any method known or familiar in the art.

In some exemplary embodiments, the surface treated fibers may be dried, for example, by pulling the fibers through a dryer, such as an oven. In some exemplary embodiments, the oven is an infrared or convection oven. The oven may be a non-contact oven, meaning that the carbon fiber tow is pulled through the oven without being contacted by any portion of the oven. The oven temperature can be any temperature suitable for suitably drying the coating composition on the carbon fibers. In some exemplary embodiments, the oven temperature is from about 230 ° F to about 600 ° F, or from about 300 ° F to about 500 ° F.

Once dried, the surface treated fibers can be wound by a winder to produce high stiffness fiber packages, or the fibers can be used immediately in downstream processes, such as for compounding with thermoplastic compositions in long fiber thermoplastic compression molding processes, or chopped for use in compounding processes, such as SMC. In some exemplary embodiments, the surface treated high stiffness fiber tows are used to produce hybrid assembled rovings, as described in PCT/US15/54584, the disclosure of which is incorporated herein by reference.

In forming fiber reinforced composites, prepregs, fabrics, non-woven fabrics, and the like, the polymeric resin matrix material may comprise any suitable thermoplastic or thermoset material, such as polyester resins, vinyl ester resins, phenolic resins, epoxy resins, polyimides, and/or styrenes, and any desired additives, such as fillers, pigments, UV stabilizers, catalysts, initiators, inhibitors, mold release agents, and viscosity modifiers, among others. In some exemplary embodiments, the thermoset material comprises a styrenic resin, an unsaturated polyester resin, or a vinyl ester resin. In structural SMC applications, the polymer resin film may comprise a liquid, while in class a SMC applications, the polymer resin matrix may comprise a paste.

In some exemplary embodiments, the surface treatment imparts increased stiffness to the reinforcing fibers. For example, the surface-treated reinforcing fiber exhibits at least a 50% increase in stiffness, or at least a 60% increase in stiffness, or at least a 70% increase in stiffness, or at least an 80% increase in stiffness, or at least a 90% increase in stiffness, or at least a 100% increase in stiffness, as compared to an otherwise identical reinforcing fiber that has not been surface-treated. The stiffness imparted to the fibers is tunable (i.e., tunable properties).

In some exemplary embodiments, the surface treatment imparts a higher loft to the reinforcement fibers that have been cut. Higher truncated bulkiness (loft) results in higher truncated density, which may affect the ability of the truncated fibers to wet out in the resin matrix material. In particular, with respect to carbon fibers, the carbon fiber tow may be divided into a plurality of finer carbon fiber bundles, each bundle comprising no greater than about 15,000(15k) carbon filaments. This separate carbon fiber tow further increases the density of the truncated loft. In some exemplary embodiments, the carbon fiber bundle comprises less than about 12,000 carbon filaments, or less than about 10,000 carbon filaments, or less than about 9,000 carbon filaments, or less than about 8,000 carbon filaments, or less than about 7,000 carbon filaments, or less than about 6,000 carbon filaments, or less than about 5,000 carbon filaments, or less than about 4,000 carbon filaments, or less than about 3,000 carbon filaments, or less than about 2,000 carbon filaments, or less than about 1,000 carbon filaments. In some exemplary embodiments, the carbon fiber tow comprises from about 1,000 to about 12,000 carbon filaments, or from about 2,000 to about 6,000 carbon filaments, or from about 2,000 to about 3,000 carbon filaments. The carbon fiber bundle has a diameter of about 0.5mm to about 4.0mm, or about 1.0mm to about 3.0 mm.

In some exemplary embodiments, the surface treatment improves the compatibility of the reinforcing fibers with the polymeric resin matrix material used in the composite production. The compatibilization of the carbon fibers with the matrix material enables the carbon fibers to flow and wet properly, thereby forming a substantially uniform dispersion of the carbon fibers within the polymer matrix material. The surface treatment also enhances cohesion, thereby improving the fiber cut and improving wettability during consolidation.

In addition, the surface treatment improves the ability to treat carbon fiber tows by reducing the occurrence of fuzz, fiber breakage, and/or fiber abrasion as compared to otherwise identical carbon fibers coated with only the sizing composition. When carbon fibers are chopped for downstream processing, the formation of fuzz prevents the chopped fibers from dispersing in the matrix material. Thus, by surface treating the carbon fibers, the formation of fuzz is reduced, thereby improving fiber dispersion.

As noted above, it has been found that the surface treatment can be tailored to "tune" the specific properties obtained by the treated fibers. For example, the surface treatment may be adjusted to increase or decrease fiber stiffness and/or bulk. Such adjustments include increasing or decreasing the surface treatment solids content (LOI), exposing the surface treated fibers to varying temperatures at different rates, adjusting the moisture content of the surface treated fibers, adjusting the angle of contact points encountered by the fibers, changing the particular type of surface treatment applied to the fibers, and/or combining various surface treatments.

In some exemplary embodiments, stiffened reinforcing fibers are used as large rigid strips (at least 24k) in the formation of composite materials, such as in the formation of wind turbine blades. As a result of using the surface treatment disclosed herein, the rigid fiber tape has a low solids content (0.5 to 3.0 wt% solids), which results in improved composite properties.

The stiffened reinforcing fibers may then be used to form a reinforcing material, such as a reinforced composite, prepreg, fabric, nonwoven, and the like. In some exemplary embodiments, the coated fibers may be used in sheet molding compound ("SMC") applications to form SMC materials. During SMC production, a layer of polymeric film (e.g., a polyester resin or vinyl ester resin pre-blend) is metered onto a plastic carrier sheet that includes a non-adhesive surface. Reinforcing fibers are then deposited on the polymer film, and a second, non-adhesive carrier sheet comprising a second layer of polymer film is placed on the first sheet such that the second polymer film contacts the reinforcing fibers and forms an interlayer material. This sandwich material is then compacted to distribute the polymer resin matrix and fiber bundles throughout the SMC material, which is then rolled for later molding processes.

In the production of SMC compounds, it is desirable that the reinforcing material is in uniform contact and mixed within the polymer matrix material. One way of such uniform mixing is known as wetting, which is a measure of the extent to which the reinforcement material is encapsulated by the matrix resin material. It is desirable to have the reinforcement material fully wetted without dry fibers. Incomplete wetting in this initial process can adversely affect subsequent processing and the surface properties of the final composite. For example, poor wetting may result in poor molding characteristics of the SMC, resulting in low composite strength and surface defects in the final molded part. The productivity of the SMC manufacturing process, such as line speed and productivity, is limited by the degree and speed at which the fibers can be fully wetted.

The SMC material may then be stored for 2-5 days to allow the resin to thicken and mature. During this maturation time, the viscosity of the SMC material increases in the range of about 1500 to about 4000 kilo-centipoise.

Once the SMC material reaches the target viscosity, the SMC material may be cut and placed into a mold having the desired shape of the final product. The mold is heated to an elevated temperature and closed to increase the pressure. This combination of high temperature and high pressure causes the SMC material to flow and fill the mold. The matrix resin then undergoes a maturation period in which the material continues to increase in viscosity in the form of a chemical thickening or gel. Exemplary molded composite parts formed using the coated reinforcing fibers may include exterior automotive body parts and structured automotive body parts.

In some exemplary embodiments, the resulting SMC material has a tensile modulus from about 10GPa to about 35GPa, or from about 15GPa to about 30GPa, including all combinations and subranges subsumed therein. In other exemplary embodiments, the resulting SMC material has a tensile modulus of from about 22GPa to about 29GPa, or about 26GPa, including all combinations and subranges subsumed therein.

In some exemplary embodiments, the resulting SMC material has a tensile strength of from about 50MPa to about 300MPa, or from about 100 to about 250MPa, including all combinations and subranges contained therein. In other exemplary embodiments, the resulting SMC material has a tensile strength of from about 160MPa to about 210MPa or about 200MPa, including all combinations and subranges contained therein.

In some exemplary embodiments, the resulting SMC material may have a flexural modulus of from about 10GPa to about 40GPa, including from about 12GPa to about 35GPa, from about 15GPa to about 30GPa, including from about 21GPa to about 26GPa, including all combinations and subranges subsumed therein. In other exemplary embodiments, the resulting SMC material has a bending strength of from about 200MPa to about 500MPa, including from about 250MPa to about 400MPa, from about 300MPa to about 360MPa, and from about 3200 to about 345MPa, including all combinations and subranges subsumed therein.

Having generally described various aspects of the general inventive concept, a further understanding can be obtained by reference to certain specific examples illustrated below. These examples are provided for illustrative purposes only and are not intended to be limiting unless otherwise specified.

Examples

The surface-treated fibers and untreated fibers were subjected to a "drape test". The surface treatment was a coating composition comprising a PVP film former and was applied at an LOI of about 2.0%. During the drape test, the fibers were cut to a length of 8 inches. The fiber is attached to a measuring bar (e.g., a ruler) and the distance measured along the x-axis is measured. Using this measurement, a perfectly straight fiber would measure 8 inches across, with less sagging fiber, as gravity overcomes the stiffness of the fiber and pulls it down.

Figure 1 shows various reinforcing fibers subjected to a drape test. It should be noted that each of the samples in fig. 1 was tested after winding except for the surface-treated carbon fiber tape, and thus part of the decrease in stiffness may be attributed to the winding process. As shown in fig. 1, the distance from the overhang point to the tip of the untreated carbon fiber tow (g) is about 3.75 inches. In contrast, the size of the surface treated carbon fiber tows (c) and 50k of the surface treated carbon fiber tape (h) is about 7.25 to 8 inches, which increases the stiffness by 93 to 113%. Similarly, the size of the surface treated glass multi-start roving (f) is about 7.875 to 8 inches, compared to 4.25 to 6 inches for the non-surface treated glass multi-start roving (e). This indicates a 33% to 85% increase in stiffness. The hybrid assembled roving (d) (mixed glass and surface treated carbon multi-end roving) measured about 4.875 to 7.5 inches (glass) and 7.625 to 8.0 inches (surface treated carbon). In addition, both the 6k surface-treated carbon fiber (b) and the 2k surface-treated carbon fiber bundle (a) measured higher than 6.0 inches compared to the untreated carbon ribbon (g) having a measured value of 3.75 inches. Table 1 lists this information in detail below.

TABLE 1

As shown in fig. 2, the surface-treated carbon fibers (multi-headed carbon fibers and carbon fiber ribbons) achieve a range of adjustable stiffness and improved stiffness relative to the stiffness of otherwise identical carbon fibers without surface treatment ("as-is" carbon fibers).

As shown in fig. 3, the surface treated multi-end glass roving achieves an adjustable range of stiffness and improved stiffness relative to an otherwise identical glass fiber that has not been surface treated ("as-is" glass fiber).

Although various exemplary embodiments have been described and suggested herein, it should be understood that numerous modifications may be made thereto without departing from the spirit and scope of the general inventive concept. All such modifications are intended to be included within the scope of this invention, which is limited only by the following claims.

All references to singular features or limitations of the present disclosure shall include the corresponding plural features or limitations and vice versa unless otherwise indicated herein or clearly contradicted by context of reference.

All combinations of method or process steps used herein can be performed in any order, unless otherwise specified or clearly contradicted by context corresponding to the recited combination.

The method may comprise, consist of, or consist essentially of the process steps described herein, or any additional or optional process steps described herein or otherwise useful.

In some embodiments, various concepts of the invention may be utilized in conjunction with each other (e.g., one or more of the exemplary embodiments of first, second, etc. may be utilized in conjunction with each other). In addition, any particular element recited in relation to a specifically disclosed embodiment should be construed as available for use with all disclosed embodiments unless the inclusion of the particular element would conflict with the wording terminology of the embodiment. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details, representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concept.