WO2014089001A1

WO2014089001A1 - Post-coated carbon enhanced reinforcement tow and chopped strands and method for forming same

Info

Publication number: WO2014089001A1
Application number: PCT/US2013/072743
Authority: WO
Inventors: Teresa Wagner; Stephanie Ann RINNE; Scott William SCHWEIGER; William Edwin SMITH; Desmond VANHOUTEN; Leonard J. Adzima
Original assignee: Ocv Intellectual Capital, Llc
Priority date: 2012-12-05
Filing date: 2013-12-03
Publication date: 2014-06-12

Abstract

A post-coated carbon enhanced reinforcement ("CER") chopped strand including a CER chopped strand that includes at least one reinforcement fiber having a plurality of carbon nanostructures ("CNSs") disposed thereon. The CNSs extend from the at least one reinforcement fiber. The post-coated carbon enhanced reinforcement further includes a post- coat composition substantially coating the CER chopped strand, forming a post-coated CER chopped strand.

Description

POST-COATED CARBON ENHANCED REINFORCEMENT TOW AND CHOPPED STRANDS AND METHOD FOR FORMING SAME

RELATED APPLICATIONS

[0001] The present application claims priority to U.S. provisional application no.

61/733,672, filed on December 5, 2012, which is hereby incorporated by reference in its entirety.

FIELD

[0002] The general inventive concepts relate generally to carbon enhanced reinforcement (CER) fibers, and more particularly, to post-coated CER tow and post-coated CER chopped strands for improved thermoplastic processing. A method for manufacturing a post-coated CER tow and post-coated CER chopped strands with improved properties and dispersibility is also provided.

BACKGROUND

[0003] Fibers, such as glass fiber, carbon fiber, carbon enhanced reinforcement (CER) fiber, metal fiber, natural fiber, synthetic fiber, or combinations thereof, or the like, are widely used for many different purposes. For example, glass fibers are used as reinforcements in polymeric matrix material to form glass fiber reinforced composites.

[0004] There has been an increasing interest in developing conductive polymer composites including carbon nanotechnology due to their superior electrical, thermal and mechanical properties. These properties make carbon nanomaterials useful as additives in various structural materials.

[0005] Carbon nanostructures (CNSs) include carbon nanomaterials, such as carbon nanotubes, for example, that have unique properties that position them for a wide scope of possible applications in suspensions and polymer based solutions, melts, and composites. CNSs are fullerene-related structures of graphite cylinders with unique atomic structures that provide high mechanical properties, namely tensile strength and elastic modulus, excellent thermal and electrical conductivities, and high aspect ratios. One type of CNS includes carbon nanotubes ("CNTs"), which are generally un-branched and may comprise single walled carbon nanotubes (SWCNTs), double walled carbon nanotubes (DWCNTs), and multi- walled carbon nanotubes (MWCNTs).

[0006] The unique structure of CNSs manifest both electrical and thermal conductivity, high strength, stiffness, and very high aspect ratios. Discovery of these structures has enabled the development of electrically conductive polymeric composites finding use in automotive applications, aerospace applications, battery applications, thermal management applications, electromagnetic interference (EMI) shielding applications, and many other applications.

[0007] However, CNSs exhibit strong van der Waals forces that attract individual CNSs to one another, causing the CNSs to aggregate into bundles, aggregates, or groupings, making dispersion of the CNSs difficult. However, the development of carbon enhanced reinforcement ("CER") fibers has led to an improvement in the dispersibility of CNSs. CER fibers comprise CNSs grown in situ on fiber substrates, or otherwise affixed, adhered, bonded, or attached to fiber substrates.

[0008] Various methods have been developed for growing CNSs on fiber substrates, or otherwise affixing, adhering, bonding or otherwise attaching CNSs to fiber substrates to form carbon enhanced reinforcement (CER) fiber. The CNSs grow radially outward from the fiber substrates in a random and structurally entangled manner, forming a percolated network as they grow. Percolation is the formation of well connected pathways of conductive media. The CNSs generally remain directly bonded to the individual fiber substrates throughout processing, such that the fibers act as a scaffold to assist in dispersing CNSs throughout a dispersion media. By grafting or otherwise bonding or adhering individual CNSs to the fibers, the CNSs are pre-dispersed over the surface of the fiber substrate. If the CNSs are not adhered to a substrate, the attractive forces of the CNSs tend to cause the CNSs to agglomerate. It is believed that growing the CNSs on the substrate, or otherwise tethering, grafting, bonding the CNSs to the substrate, aids in the dispersion of the CER in a media and thereby the overall formation of a percolated network.

[0009] CER fibers may be included in matrix materials for formation of composite materials that provide such functions as reinforcement and electromagnetic shielding. Composite reinforcements have been developed where CER fibers are compounded into matrix materials to provide end products, such as EMI shielding.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figures l(a)-(c) illustrate an exemplary process in which a CER tow (1(a)), is post- coated (1(b)), and dispersed in a matrix material (1(c)). [0011] Figure 2 illustrates an exemplary post-coating process.

[0012] Figure 3 illustrates an exemplary process for chopping a post-coated CER tow.

[0013] Figure 4 illustrates various aspects of an exemplary post-coating process, including an exemplary comb to guide CER fiber tows into a post-coat bath (left top and bottom) and an exemplary stripper die (right top and bottom).

[0014] Figures 5(a) and (b) illustrate histograms of the average moisture uptake and solids content for various exemplary post-coated CER samples.

[0015] Figure 6 illustrates a comparison between exemplary in-line dried post-coated CER tow and post-coated CER chopped strands post-coated with both low and high solids loadings.

[0016] Figure 7 illustrates a comparison between exemplary offline and in-line dried post- coated CER tow and post-coated CER chopped strands.

[0017] Figures 8 illustrates an exemplary process for chopping a post-coated CER fiber tow.

[0018] Figures 9-1 1 illustrate the degree of post-coated CER fiber aggregates in various CER composite samples.

DETAILED DESCRIPTION

[0019] While various exemplary methods and materials are described herein, other methods and materials similar or equivalent to those described herein are encompassed by the general inventive concepts. All references cited herein, including published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, and any other references, are each incorporated herein by reference in their entireties, including all data, tables, figures, and text presented in the cited references.

[0020] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. In this connection, unless otherwise indicated, concentrations of ingredients given in this document refer to the concentrations of these ingredients in the master batch or concentrate, in keeping with customary practice.

[0021] As used herein, the terms "sizing agent," "fiber sizing agent," or "sizing," refer collectively to compositions used in the manufacture of fibers as a coating to protect the integrity of fibers, provide enhanced interfacial interactions between a fiber and a matrix material in a composite, and/or alter and/or enhance particular properties of the fibers.

[0022] In accordance with customary practice, the term "fiber" or "fiber material" refers to any material which has a fibrous structure as its elemental structural component. The term encompasses fibers, filaments, yarns, tows, tapes, woven and non-woven fabrics, plies, mats, and the like.

[0023] The general inventive concepts relate to a post-coated CER fiber tow and post-coated CER chopped strand and the process of manufacturing the post-coated CER tow and post- coated CER chopped strand to improve the downstream processing capability of the CER fibers. As used herein, the terms "CER," "CER fiber," "CER strand" and "CER fiber tow" refer collectively to fibers that include carbon nanostructure (CNS) grown in situ thereon. It should be understood that the general inventive concepts relate also to CER fiber which have not had CNSs grown in situ thereon, but rather CER fibers that include CNSs that are affixed, adhered, attached or otherwise bonded thereto. The post coating may be used for a variety of purposes, such as protecting the CNS growth on the fibers, improving the fiowability and processability of the CER fibers in a matrix, while maintaining dispersibility, and/or encapsulating the CNSs for health and safety purposes.

[0024] The CNSs used in the CER fiber structures may be formed according to any suitable nanostructure forming process, including conventional processes. The forming process may include growing a novel material composed of carbon nanostructures (CNSs) directly on a reinforcing fiber tow through a continuous chemical vapor deposition (CVD) process, which allows the CNSs to take on the dimensionality of MWCNTs. The input reinforcing substrate may comprise any conventional material, such as glass fibers, carbon fibers, and the like. The term "reinforcing" means the substrate may impart some beneficial or otherwise desirable property (e.g., increased strength) to another substrate or material. Other reinforcing substrates are also contemplated herein such as woven and non-woven fabrics, glass spheres, and the like. Although the reinforcing fibers will be described herein as glass fibers, it is to be appreciated that any conventional reinforcing fiber may be used.

[0025] The glass may include any type of glass suitable for a particular application and/or desired product specifications, including conventional glasses. Non-exclusive examples of glass compositions include A-type glass fibers, C-type glass fibers, AR-glass fiber, E-type glass fibers, S-type glass fibers, E-CR-type glass fibers (e.g., Advantex® glass fibers commercially available from Owens Corning), R-type glass fibers, wool glass fibers, or combinations thereof, which may be used as the reinforcing fiber. In some exemplary embodiments, the glass has both a high Young's modulus and high tensile strength, and may maintain some of these properties even in the presence of CNS growth and/or related processing, such as Young's modulus. In some exemplary embodiments, the input glass is Advantex® glass as a low cost, boron free E-glass and E-CR glass reinforcement. [0026] Alternatively, the reinforcing fiber may be fibers of one or more synthetic polymers such as polyester, polyamide, aramid, and mixtures thereof. The polymer strands may be used alone as the reinforcing fiber material, or they can be used in combination with glass fibers such as those described herein.

[0027] Exemplary structural fibrous materials include glass, in the form of glass fibers; carbon or graphite in the form of carbon or graphite fibers; non-graphite carbon fibers; vitreous carbon fibers; boron monolithic graphite and monolithic non-graphite carbon fibers; silicon; aramid; and other refractory materials. In addition, thermoplastic fibrous material may be used.

[0028] The glass fibers may be formed in any desired shape, such as, for example, circular, oval, ellipse, hollow, flat, rectangular, and square. The glass fibers may be formed having diameters ranging from about 2.0 microns to about 30.0 microns. In some exemplary embodiments, the fibers have a diameter from about 5.0 microns to about 24.0 microns. In some exemplary embodiments, the fibers have a diameter between 9.0 and 13.0 microns. However, it should be understood that any suitable diameter of fiber may be used.

[0029] The glass fiber input may be continuous or it may be chopped, segmented, or otherwise discontinuous. In some exemplary embodiments, the fibers are in the form of a continuous fiber tow. If the fibers are chopped, they may be sheared into segments having discrete lengths. In some exemplary embodiments, the chopped fibers may have a length of approximately 3.0 mm to about 25.0 mm in length. In some additional exemplary embodiments, the fibers have a length from about 20.0 mm to about 35.0 mm.

[0030] The individual glass fibers are loosely associated into a tow, which is a bundle of twisted or untwisted filaments or untwisted groups of fibers. Tex is a unit of measure for the linear mass density of fibers and is defined as the mass in grams per 1000 meters. In some exemplary embodiments, the tows may vary in weight and comprise a tex range that is generally between 100 and 9600, and particularly between 300 and 4800. In some additional exemplary embodiments, the tex range is between 400 and 735. If the fibers have a diameter of about 24 micron in a 4000 fiber roving, the tex is 4800. With diameters of about 9 or 10 micron, the tex is 400. In some exemplary embodiments, the tow is a 2000 fiber roving having 400 tex.

[0031] In some exemplary embodiments, the tows are wound on winders to collect the continuous glass fiber tows into wound packages, such as doffs or cakes. The wound packages may then be placed in an oven to evaporate the water in the sizing components and further processed in a number of ways. [0032] According to the general inventive concepts, the CNSs may be formed on the fiber substrates according to any suitable nanostructure forming process, including conventional processes, such as, for example, U.S. Patent Number 8,158,217 and U.S. Published Application Number 2010/0279569, each incorporated herein by reference in their entirety. In some exemplary embodiments, the forming process includes growing CNSs in situ on fiber substrates, or otherwise affixing, adhering, bonding, or attaching the CNSs to fiber tows using a process called continuous chemical vapor deposition (CVD). The CVD process allows the composition and structure of the CNSs to be tuned, selected, or otherwise controlled to tailor the properties of the resulting composite to the specific application needs. Such "tunable" properties include physical properties, such as density and thickness; mechanical properties, such as toughness and isotropy; thermal properties, such as heat stability and conductivity; electrical properties, such as shielding, storing, directing, and absorbing; and durability properties, including corrosion, wear, and fatigue resistance.

[0033] In some exemplary embodiments, the CVD process includes catalytic or autocatalytic decomposition of carbon precursor molecules on the surface of a catalyst deposited on a support. In some exemplary embodiments, the carbon precursor is provided by a carbonaceous gas such as, for example, acetylene, methane, ethylene, nitrogen, and the like. In one exemplary embodiment, the gas comprises acetylene. This catalytic decomposition may be followed by diffusion of the carbon atoms that are subsequently produced. CNS growth may take places at the location of a catalyst particle. The catalyzed fiber may be fed into an enclosed heated chamber where the CNS growth occurs. The heated enclosed chamber supports an atmosphere including one or more chemical gases. The gas or gas mixture is introduced into the chamber to initiate CNS growth on the fibers. The gas is introduced or heated to a temperature sufficient to cause the carbon atoms from the carbon source to disassociate.

[0034] In some exemplary embodiments, CNSs grow directly on a glass fiber as cross-linked structures. The glass fibers with CNSs may be used without purification as a fiber tow, allowing for direct application into an industrial polymer process such as compounding.

[0035] In some exemplary embodiments, the CNSs grow radially outward from the glass fibers in a random and structurally entangled manner, forming a percolated network as they grow. Percolation is the formation of well connected pathways of conductive media. The individual CNSs may be branched and/or cross-linked, forming an entangled growth network. The percolation of the CNSs provides enhanced electrical conductivity for greater electrical performance. In some exemplary embodiments, the CNS branching may stem from catalyst particles that becomes deposited or located on individual CNSs. [0036] The CNSs may be CNTs that are single walled, or may include any number of walls, such as between 2 and 12 walls or more. In some exemplary embodiments the CNSs include between 4-8 walls. In some exemplary embodiments, the CNSs have 6 +/- 2 walls. The CNSs may vary in size, such as having inside diameters from about 2 nm to about 8 nm. In some exemplary embodiments the CNSs have inside diameters between about 3 nm and about 6 nm. In some exemplary embodiments, the CNSs may have outside diameters between about 5 nm and 20 nm and more. In some exemplary embodiments the CNSs have outside diameters between about 6 to about 10 nm. The CNSs may have lengths from about 5 microns to about 200 microns, and more particularly between 80 and 120 microns.

[0037] The CNS loading on the fiber substrates, forming the CER fibers, may be of any loading level desired for a particular application. In some exemplary embodiments, the CNS loading on the fiber substrate may be between about 1 and about 50 weight % loading on the fibers. In some exemplary embodiments, the CNS loading may be between about 10 and about 30 weight % loading on the fibers. In yet other exemplary embodiments, the CNS loading may be about 17 to 18 weight % loading. The amount of CNSs grown on the glass fibers may have a large effect on the properties of a downstream article. The CNS loading may be optimized for obtaining the desired properties of the downstream article. However, the level of CNS loading may be reduced to meet particular performance requirements, reduce costs, and improve the molding of final parts. Minimizing the CNS loading on the glass tow may allow the line speeds of the growth process to be increased, which leads to a reduction in the time required to produce the material and ultimately to produce a part at a reduced cost.

[0038] In some exemplary embodiments, the CER tow is post-coated by feeding the CER tow into a bath containing a polymeric post-coat composition. The fibers can be fed into the bath in the form of a CER tow or as individual fibers. The tow or individual fibers may be pulled to and from the bath using a puller, such that the tow or individual fibers are dipped though the bath, which enables each fiber to be generally uniformly coated with the post-coat composition.

[0039] In some exemplary embodiments, the post-coat composition may be aqueous or nonaqueous and include a variety of components, such as, for example, film formers, coupling agents, viscosity modifiers, and additives, such as, but not limited to lubricants, surfactants, anti-oxidants, and plasticizers. The particular chemistry selected for the post-coat composition is important, such as not to cause fiber brittleness or other negative fiber properties. In some exemplary embodiments, the post-coat composition has a solids content of between approximately 0.5% and about 10.0%, however any suitable solids content may be utilized.

[0040] Generally, the film formers for the post-coating composition are generally capable of coating the individual CER fibers or the CER tow as a whole. For example, suitable film formers include, but are not limited to waxes, polyethylene glycols, polypropylene glycols, polycaprolactones, glycidyl ethers, epoxy resins, urethanes, polyester alkyds, amic acid, propylene glycol fumarate, propoxylated bisphenol-A-maleate, propoxylated allyl alcohol- maleate, polyvinyl acetates, olefins, surfactants, maleated polypropylene, low molecular weight polyesters and mixtures thereof. Particularly, in some exemplary embodiments, the film former includes one or more of a polyurethane, such as Hydrosize® U6-01 and/or Baybond® PU 401 ; polypropylene; polyethylene glycol ester, such as PEG 400 MO; polyvinylpyrrolidone (PVP), such as PVP K-15, PVP K-30, PVP -90, PVP K-60, and PVP K-120; and epoxy resin, such as EPI-REZ™ 351 1. Additionally, the film former may include one or more surfactant, such as a nonionic surfactant (i.e., Triton X-100), for example.

[0041] The coupling agent may comprise any coupling agent desired for a particular application. In some exemplary embodiment, the coupling agent used in the post-coating composition may include one or more of alcohols, amines, esters, ethers, hydrocarbons, siloxanes, silazanes, silanes, lactams, lactones, anhydrides, carbenes, nitrenes, orthoesters, imides, enamines, imines, amides, imides, functionalized olefins and mixtures thereof. Particularly, in some exemplary embodiments, the coupling agent is a silane selected from one or more of BM-602 (N-(-aminoethyl)— aminopropylmethyldimethoxysilane), (gamma-

2- aminoethylamino)propyl metliol dimethoxysilane, aminopropyldiethoxysilane, gamma- aminopropyltriethoxysilane (A1 100), gamma-glycidoxypropyltrimethoxysilane (A-187) and

3- methacryloxypropyltriinethoxysilane (A-l 74).

[0042] As stated above, the inventive post-coating composition may include additional various additives. In some exemplary embodiments, the post-coating composition includes a viscosity modifier, including, but not limited to a water soluble polymer, such as an acrylic polymer. Such an acrylic polymer may include a polyacrylamide, such as Drewfloc 270. In some exemplary embodiments, the post-coating composition includes a curing agent. The curing agent may comprise dicyandimide (DICY), which is a known curing agent for epoxy resins. In some exemplary embodiments, the inventive post-coating composition may further include adhesives, such as, for example, an ethylene-vinyl acetate copolymer emulsion (i.e., Airflex® 410). The post-coating composition may further include polyvinylfornmldyde/polyvinylamine or copolymers, which may be obtained from various sources, including Lupamin® 9095, 9050, 9000, 5095, and 1500, for example.

[0043] The post-coating composition may further include surfactants, such as, for example, non ionic surfactants. Exemplary nonionic surfactants may include long chain alcohols, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, glucoside, alkyl ethers, polyoxyethylene glycol alkylphenol ethers, glycerol alkyl esters, polyoxyethylene glycol sorbitan alkyl esters, sorbitan alkyl esters, polyethoxylated tallow amine, cocamide DEA, cocamide MEA, dodecyldimethylamine oxide, poloxamers, polyethyleneamine polyamide salts, ethoxylated acetylenic diols, and octylphenoxypolyethoxyethanol.

[0044] In some exemplary embodiments, the inventive post-coat composition comprises one or more of a film former, a coupling agent, and optional additives. In some exemplary embodiments, the post-coat composition comprises from about 70 to about 99 weight percent film former, about 1 to about 30 weight percent coupling agent and about 0 to about 20 weight percent of optional additives. In other exemplary embodiments, the post-coat composition includes about 80 to about 90 weight percent film former, about 10 to about 20 weight percent coupling agent, and about 0 to about 10 weight percent additive.

[0045] In some exemplary embodiments, the post-coated CER tow maybe chopped to form post-coated CER chopped strands that may be used in downstream processing, such for compounding with a matrix material for use in end use products, such as, electrical and thermal transport applications. For example, the post-coated CER chopped strands may be used to form end products exhibiting EMI shielding, electrostatic discharge (ESD) shielding, lighting strike shielding, radio frequency interface shielding, and the like. Any suitable matrix material may be used, such as, for example, resins (polymers, monomers, or oligomers), both thermosetting and thermoplastic; metals (such as aluminum, titanium, iron, and copper); ceramics (such as silicon carbide, boron carbide, and boron nitride); and cements, or a combination thereof. Thermoplastic resins may include, for example, acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), polysulfones, polyamides, polyethylenimine (PEI), polycarbonates, polyphenylene oxides, polysulfides, polyether ether ketones (PEEK), poly ether ketone (PEK), polyphenylene sulfide (PPS), polyurethane (PU), polystyrene, polyether sulfones, polyamide-imides, polyetherimides, polyimides, polyarylates, polyphthalamide, acrylic styrene acrylonitrile, polyphenylene ether, polyolefins, polyester, rubber (SBR), butadiene nitrile rubber (BNR), ethylene propylene diene monomer rubber (EPDM), fluoropolymer (FP), liquid crystalline polyester, and other thermoplastics and alloys of thermoplastics. In some exemplary embodiments, the matrix material comprises a thermoplastic resin that is selected from ABS, polycarbonate, polyamides, and combinations thereof. Thermoset resins may include, for example, epoxies, polyesters, phenolics, vinyl esters, polyimides, and the like.

[0046] As illustrated in Figure 1(a), CNSs create a "bulky" tow by extending radially from a fiber. Therefore, the overall diameter of the CER tow is larger diameter than a typical glass fiber tow. By post-coating the CER tows, the CNSs are condensed around the CER tow, as shown in Figure 1(b). The condensed CER fibers may then be chopped and mixed with a matrix material and the CER fibers and associated CNSs are dispersed throughout the matrix, as illustrated in Figure 1(c).

[0047] In some exemplary embodiments, applying the post-coat composition to the CER tow improves the processability of the CER chopped strands, at least by condensing the CNSs and allowing for easier handing of the CER chopped strands. Uncoated CER chopped strands are generally difficult to process due to the buildup of fuzz and the limitations and difficulties in feeding the CER chopped strands into downstream processing machines due to the low bulk density of the strands. The term "fuzz," as used herein, refers to the broken glass filaments that break off from a bundle. Fuzz can accumulate on processing equipment, which may negatively affect downstream processing. However, although post-coating improves the ability to process CER chopped strands downstream, conventional wisdom would lead one to believe that dispersibility of the CER chopped strands would be negatively affected by the post-coating, since rather than exploiting the outwardly radiating nature of the CNSs and maximizing the presence of CNSs in a matrix material, the CNSs are consolidated. However, unexpectedly, the dispersibility of the CER chopped strands is maintained at a level at least comparable, if not improved, over non-post-coated CER chopped strands. Therefore, in some exemplary embodiments, the present post-coating process improves the processability and handling of CER chopped strands without reducing CNS dispersibility.

[0048] The particular chemistry of the post-coat composition may be selected to be at least semi-compatible with the particular matrix material used, which may aid in the dispersion of the CER chopped strands throughout the matrix material. Additionally, in some exemplary embodiments, the softening temperature of the post-coat composition is equal to or less than the processing temperature of the matrix material. Therefore, as the post-coated CER chopped strands are compounded with a matrix material, the post-coat composition flows and the CNSs on the CER chopped strands to disperse and un-densify. Therefore, both the CER chopped strands and the CNSs individually are able to disperse in the matrix material as the post-coat composition softens and begins to flow. [0049] In some exemplary embodiments, applying the post-coat composition to the CER tow provides the additional benefit of protecting the individual CNSs formed on a fiber and helping to maintain the CNSs on the fiber during downstream processing. By encasing the CNSs in a post-coat, the CER tows and subsequently formed CER chopped strands may be safely handled and easily processed in downstream materials.

[0050] The CER/matrix material composites may be pelletized to form composite pellets. The composite pellets may be re-processed and/or re-pelletized one or more times to further enhance dispersion, although such reprocessing steps are not necessary with the dispersion of the post-coated CER. In some exemplary embodiments, it is beneficial that the moisture is removed from the pellets by drying prior to any processing or injection molding. The drying may be performed by any suitable drying means.

[0051] The particular CNS loading in a post-coated CER composite may vary depending on the particular application that the composite is to be used for. In some exemplary embodiments, the post-coated CER/thermoplastic composites have a CNS loading of approximately 1 to approximately 20 weight percent CNS. In some exemplary embodiments, the CER composite pellets, having about 5 percent by weight CNS may exhibit an EMI shielding effectiveness (SE) between about 30 and 100 dB over a low frequency range (50- 2000 MHz or 0.05-2 GHz) and at a composite thickness of about 3.2 mm, measured using the method in ASTM D4935. In some exemplary embodiments, the EMI SE is at least 60 dB in the low frequency range at a thickness of about 3.2 mm. In yet other exemplary embodiments, the EMI SE is at least 80 dB in the low frequency range at a thickness of about 3.2 mm.

[0052] In some exemplary embodiments, the post-coated CER composites have a resistivity of between less than about 10^"'^"10⁹ oms*cm, and in other exemplary embodiments, the composite has a resistivity about 10^_1-10⁵ oms*cm as determined by the Van der Pauw method. In various exemplary embodiments, the post-coated CER composites, having a 5% CNS loading, have a resistivity of about 0.15 to about 0.4 ohm*cm.

[0053] The Van der Pauw method includes cutting a square of the composite material and applying silver paint to the corners. A current is then sourced to one side of the square composite by contacting probes to the painted corners. The resulting voltage is then measured using a voltmeter via probes that are connected to the painted edges on the opposite side of the square composite. This process is then repeated for each of the composite's sides. The readings from the sides that are parallel to each other are then averaged. From these averages, the sheet resistance is determined according to the following equation: ^vertical "^•^-horizontal

[0054] In this equation, R_s is the sheet resistance. When multiplied by the thickness (in cm), the sheet resistance becomes bulk resistivity in ohm*cm.

[0055] The post-coated CER composite pellets may further exhibit improved mechanical properties. Such properties are dependent upon the particular process steps implemented and also the particular materials used, which will be explained in more detail below.

Process for Producing a Post-Coated CER Fiber Tow and Post-coated CER chopped

Strands

[0056] An exemplary process for producing the inventive post-coated CER tow and post- coated CER chopped strands is shown in Figure 2. The process generally includes growing a plurality of CNSs on an input fiber tow to produce a CER tow, coating the CER tow with a post-coating composition, and chopping the post-coated CER tow to form post-coated CER chopped strands. This process is described in more detail below.

[0057] As described above, although one or more of the reinforcing fibers described herein may be used in producing the CER chopped strand, it should be noted that the exemplary process is described with respect to exemplary embodiments in which the reinforcement fibers are a single type of glass fibers. As is known in the art, glass fibers may be formed by attenuating streams of a molten glass material through a heated bushing to form substantially continuous glass fibers. The continuous fibers are bundled together according to known bundling or packaging methods to form a fiberglass roving or other package, which can in turn be used in the inventive process.

[0058] According to some exemplary embodiments, at any time during the fiber forming process, the fibers may be coated with a chemical (i.e., size) composition. In some exemplary embodiments, the size compositions used with CNSs may be silane-free, and include one or more of a film former to provide stiffness and strength, a cationic lubricant that is strongly attracted to glass and protects the glass from abrasion, and a nonionic lubricant that keeps the fibers coated and protected. Alternatively, or additionally, the fibers may be coated with a catalytic composition that includes one or more of the size ingredients described above and also a catalyst. The catalyst may take on any form, including a solid, liquid, gas, and the like. The size/catalytic composition may be applied to the fibers by any method suitable for the desired CER growth, including kiss roll, dip-coat, slide, or spray application to achieve the desired amount of catalytic composition on the fibers. [0059] A fiberglass roving coated with the size/catalytic composition then enters the CER growth processing stage, such that CNSs are grown directly (i.e., in situ) on the surface of the input fiberglass tow. The CER growth processing stage is carried out in a growth chamber and includes various steps that may occur in various sections of the growth chamber. The growth chamber may comprise a single continuous chamber, or it may comprise multiple, connected sub-chambers.

[0060] The growth processing stage may include a catalyst preparation step, in which the fibers coated with the catalytic composition are heated in a high temperature chamber to remove the size-like components and dry the liquid catalyst. The specific temperature is a function of the particular catalyst disposed on the fibers, but in some exemplary embodiments will be in the range of about 500 °C to 1000 °C. The catalyst preparation step may occur in either a separate unit preceding the growth chamber; within the growth chamber itself; or within proximity to the growth chamber. It should be understood that in various exemplary embodiments, the size-like components need not be removed.

[0061] After removal of the size components, if any, the catalyzed glass fiber may be fed into an enclosed heated chamber for the CNS growth. The heated enclosed chamber supports an atmosphere including one or more chemical gases, including a carbon source gas. The gas or gas mixture is introduced into the chamber to initiate CNS growth on the fibers. The gas may include, for example, one or more of acetylene, nitrogen, and hydrogen. In one exemplary embodiment, the gas comprises acetylene. The gas is introduced at a high temperature sufficient to cause the carbon atoms from the carbon source to disassociate.

[0062] In the presence of the catalyst, the carbon source disassociates and carbon nanostructures grow on individual filaments. The process of growing the CNSs on glass fiber structures is based on continuous, rapid, high temperature, catalyzed chemical vapor deposition, which may be tuned to tailor the loading, composition, and structure of the resulting composite to specific application needs. The deposition may be conducted in an enclosed production line so that no particles are released into the environment during production.

[0063] In some exemplary embodiments, the CER tow may then be pulled through a post- coat bath containing the post-coat composition, as illustrated in Figure 3. As described in more detail above, the post-coat composition may be an aqueous or non-aqueous based coating. The post-coat composition may include lubricants, film formers, silanes, and/or additional additives. In accordance with some exemplary embodiments, the particular post- coat composition used depends on the polymer system and performance requirements of the customer.

[0064] Prior to passing through the post-coat bath the CER tow may optionally pass over a roller or through grooves, a comb, etc., to help guide the CER fiber tow into the post-coat bath with minimized tangling and/or winding. In some exemplary embodiments, a comb is provided which includes a number of spaced apart vertical bars that may be located at the entrance to the post-coat bath. One exemplary embodiment of such a comb is illustrated in Figure 4. The vertical bars may rotate such as to limit the amount of fuzz build-up caused by friction between the tow and the vertical bars. It should be understood that a variety of suitable structures, apparatuses, and articles could be utilized to guide the CER fiber tow into the post-coat bath and the present invention is not limited to the use of the comb illustrated in Figure 4.

[0065] In accordance with some exemplary embodiments, excess moisture may be removed from the post-coated CER tow through a variety of means, including, for example, passing the post-coated CER tow through one or more forming die, such as, for example, a wire forming die. An exemplary forming die is illustrated in Figure 4 (top). As shown in Figure 4 (bottom right), the forming die may be tapered to remove excess moisture from the CER tow and further consolidate the CER tow by condensing down the individual CNSs. The forming die may be designed to condense the CNSs on the tow, while being careful not to damage the CNSs or remove the individual CNS from the CER tow. In some exemplary embodiments, the forming die has a particularly diameter and/or particular shape, such that the CER tow exits the stripper die having the approximate diameter and shape of the die.

[0066] Figure 5(a), (b) illustrates one example of moisture uptake by CER tows. In this example, post-coated CER tows were pulled through a forming die, dried, and then weighed. The weight difference between uncoated fibers and post-coated fibers was used to determine the moisture pickup of the post-coated CER fiber tow. The exemplary CER tows tested had an 800 tex and about 17.5 % CER loading in the post-coat composition. As shown in the histogram of Figure 5(a),(b), the samples provided an average moisture content of 70.6% with a forming die diameter of 78 mils (Figure 5(a)). The solids content on the fibers was averaged at 9.4% (Figure 5(b)). For the particular CER tow used in this example, a forming die diameter of 78 mils was used; however, forming dies of various suitable diameters may be used.

[0067] In some exemplary embodiments, once the post-coated CER tow is pulled through the forming die, if present, the fibers may be dried to obtain a desired final moisture content. The drying may occur in-line, off-line, or a combination of both in-line and off-line. During an exemplary in-line drying process, water from the post-coat composition is driven off a CER tow in an oven, such as a convection oven, or other heating apparatus, such that a final coating is formed on the CER tow. The final coating comprises an at least partially dried and/or cured post-coat composition. The CER tow may be pulled through an in-line drying oven that is heated to any desired temperature for a particular result. In some exemplary embodiments, the oven temperature is between approximately 350 °F-700 °F, particularly about 600 °F.

[0068] In some exemplary embodiments, the drying step occurs off-line in an oven once the CER tow has been wound wet into a spool. The wet- wound CER spool may be placed in an oven and heated at any desired temperature, such as between approximately 100-130 °C for a period of time determined to produce a desired moisture content. In accordance with various exemplary embodiments, the CER tow may also be partially dried in-line and then wound and further dried off-line. Drying the fiber tow in-line prior to winding may allow the use of a post-coating with a higher solids content (e.g. 10-15%), which has been shown to provide a better coating of a CER tow and also reduced the fuzz that is produced. Winding a wet CER tows post-coated with a composition having a high solids content may cause excessive stickiness, such that the tows stick together during winding. Pulling apart CER tows that have excessive stickiness may create fuzz on the tow. Therefore, in-line drying a CER tow post- coated with a high solids content composition may produce a post-coated CER tow with a better coating with less fuzz.

[0069] To demonstrate the effect of the solids content of post-coat compositions, post-coat compositions with differing solids content were used to post-coat CER tows and the coated tows were dried using an in-line drying process. Some of the samples were then chopped to produce post-coated CER chopped strands. One exemplary post-coat composition had a low solids content and the other exemplary composition included a solids content that was increased by a factor of 8. As illustrated in the left column of Figure 6, the post-coated CER tow produced using the post-coat composition with a lower solids content was less condensed than the tow coated with the composition having a higher solids content (Figure 6, right column). Additionally, the compositions with the lower solids content were unable to fully coat the fibers and generated fuzz and dust due to the breakage of glass filaments and CNSs falling off during processing, making downstream processing of the chopped strands difficult. In some exemplary embodiments, a higher solids content improves the quality of the coating on the fibers, reduces the fuzz and dust produced, and improves the overall chopped strand quality.

[0070] Whether a post-coated CER tow is dried off-line or inline may also effect the cross- sectional size and shape of the resulting tow. In some exemplary embodiments, tows that are wound wet and dried offline may have a wide and flattened shape, due to winding and compressing the fibers while the post-coat composition is wet. In contrast, tows that formed by the forming die and inline dried may be more consolidated and round, since the post-coat composition is able to dry prior to winding the fiber. A wide flat fiber tow may have lower bulk density, which may affect the ability of chopped fibers to flow in downstream processing. According to some exemplary embodiments, the in-line drying process produces a more consolidated strand and a higher bulk density chopped CER fiber that is more likely to flow in downstream processing (See, e.g., Figure 7). As can be seen in the exemplary embodiment of Figure 7, passing a post-coated CER tow through a forming die and then inline drying the tow may increase package density by about 2.5 times over off-line drying. Therefore, in-line drying a CER tow post-coated with a high solids content composition produced the most condensed chopped strands.

[0071] In some exemplary embodiments, the post-coated CER tow exits the in-line drying oven, if present, and is wound into one or more packages of post-coated CER fibers. The CER tow may optionally be passed through guide eyes to keep the tow(s) straight and separate, in the case of multiple tows, for winding. The winder may be a single winder, or may include multiple winders, used in conjunction. In some exemplary embodiments, the throughput of the post-coating process was doubled by including two winders in the process. Another processing variable that may improve throughput includes reducing breakouts, such as by utilizing a bath with a shallower angle to reduce abrasion, reducing the tension on the fiber tow as it moves through the process (while maintaining some tension), and changing the knot type when stringing the tow. The winder may comprise any winder generally used in the art, such as an inside pull winder that is built on a rubber bladder, or an outside pull winder that is built on a cardboard core. In some exemplary embodiments, the post-coated CER tow is wound on an inside-pull winder creating a package of up to about 12" outer diameter.

[0072] Once the post-coated fiber tow is wound into a package, the package may be effectively stored and/or used for downstream processing. To package the spools efficiently, the CER fiber spools can be placed together for collective transfer away from the growth line. Alternatively, the tow may be fed directly into a chopper for the formation of a plurality of post-coated CER chopped strands. In some exemplary embodiments, the CER package is unwound and pulled through a chopper, as exemplified in Figure 8. The chopper may comprise any conventional cutting means, such as, for example a blade cutter head that includes razor blades inserted into slots positioned a distance corresponding to the length of a desired chopped strand. The post-coated CER chopped strands produced may be of any length desired for a particular application, such as, for example, from about 1/8 inch to about 1 inch.

[0073] In other exemplary embodiments, the chopping may take place in-line, which eliminates the winding step. In some exemplary embodiments, removing the winding step allows for a more consistent output, which may provide a higher process yield of choppable material. Additionally, without the winding step, multiple tows may be chopped at once, which may increase productivity, such as, for example, increasing the CER chopped strands produced.

[0074] In some exemplary embodiments, the post-coated CER chopped strands are implemented in downstream processes, such as mixing the chopped strands with a matrix material to produce a CER/matrix material composite. In one exemplary process, the post- coated CER chopped strands are intimately mixed with the matrix material by a compounding process. In some exemplary embodiments, the post-coated CER chopped strands are fed into a compounding extruder such as, for example, a twin-screw extruder. As the post-coated CER chopped strands are introduced into a heated, polymer filled twin screw extruder barrel, the post-coating on the chopped strands softens and begins to flow. As the post-coated CER chopped strand disperses, the CNSs both on and off of the strands become intimately mixed and dispersed within matrix material. Therefore, as the post-coated CER chopped strands are mixed with the matrix material, a sufficient percentage of the matrix material includes the CNS material.

[0075] As the CER/matrix material exits the extruder, the thermoplastic matrix may be pelletized to form CER matrix material composite pellets. The composite pellets may be reprocessed and/or re-pelletized one or more times to further enhance dispersion, although such reprocessing steps are not necessary with the improved dispersion of the CER.

[0076] The pelletized CER composite pellets may further be "let down," which means diluting the composites with additional matrix material for use with different applications. The diluting matrix material may be of the same or a different type of matrix material that is initially included within the pellet. The CER composite pellets may be concentrated with CNSs, such as about 5 to about 25 weight percent CNSs, and in some exemplary embodiments, about 8 to about 12 weight percent CNSs in the pellet. The CER composite pellets may then be let down, or diluted, to lower the CNS levels. In some exemplary embodiments, the CER composite pellets are diluted to levels ranging from about 10% CNSs to less than l% CNSs.

[0077] Downstream products, such as EMI shielding articles, may be produced by processing the pelletized CER thermoplastic composite through any desired composite processing means. The composite may further be molded into a desired shape for a particular application.

[0078] Having generally described various exemplary embodiments of the general inventive concepts, a further understanding thereof can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be inclusive or limiting unless otherwise specified.

Example 1 : Post-Coat Compositions and Bulk Density.

[0079] Exemplary post-coat compositions having different chemistries were produced and used to post-coat exemplary CER tows. The exemplary tows were 800 tex and comprising 10 micron glass fibers having an 18% CNS loading. The exemplary post-coated CER tows were examined for both the coating on the stand and the bulk density of the post-coated tow. Table 1, below, lists the exemplary post-coat compositions and resulting properties.

Table 1: Exemplary post-coat compositions.

8)- Aqueous 90% A-l 100; gamma- 10% 10.7% 0.4

24B polyurethane aminopropyltriethoxysilane

solution

[0080] Higher bulk density samples generally represent a more consolidated post-coated CER tow. Exemplary post-coats 142B and 142 A (Trials 1 and 2) include only film formers and are void of any silane. These compositions illustrate how the coating on the strands may affect the resulting bulk density of the CER tow. For instance, Trial 2 included an 11.2 weight % coating on the strands compared to Trial 1 with a 4.4 weight % coating. Trial 2 resulted in a higher bulk density than Trial 1 , which indicates that the amount of post-coating on the strands may influence the resulting bulk density. Additionally, Trial 3 includes the addition of a silane and has a similar coating percentage on the strands. However, Trial 3 achieves a higher bulk density, indicating that the addition of a silane is important in achieving a high bulk density.

[0081] Trials 4-6 further exemplify the influence that the amount of post-coating may have on the bulk density of a resulting post-coated strand. Trial 4 included only a 1.7 weight % coating and demonstrated the lowest bulk density at 0.1 g/ml, while Trial 5, with a 6.8 weight % coating resulted in a bulk density of 0.18 g.ml and Trial 6, with a 13.5 weight % coating resulted in the highest bulk density, at 0.21 g/ml.

[0082] Trials 7 and 8 illustrate the importance of selecting the proper film former when optimizing bulk density. Trial 7 includes an aqueous polyurethane dispersion as the film former and Trial 8 includes an aqueous polyurethane solution. Although Trial 7 used a higher weight percent of post-coating on the strands, Trial 8 nonetheless resulted in a higher bulk density. Therefore, it is believed that using an aqueous polyurethane solution may result in a higher bulk density than using an aqueous polyurethane dispersion. This difference may be attributed to the particles present in the dispersion, which may make it more difficult for the polyurethane to penetrate into the CNS, while a solution may better wet the CNS. However, coatings comprising polyurethane dispersion are still acceptable for use in the inventive post- coat composition.

[0083] Trials 6 and 8 further illustrate the affect that the selection of silane may have on the resulting bulk density of a post-coated CER tow. Trial 6 includes a 3-aminopropyl methyldiethoxy silane, while Trial 8 includes a gamma-aminopropyltriethoxysilane. Each post-coat composition included the same type of film former and included the silane and film former in the same amounts. Therefore, the only difference was the type of silane used and the amount of coating on the strands. Although Trial 6 had a higher coating percentage at 13.5 weight %, Trial 8, using the gamma-aminopropyltriethoxysilane, resulted in a higher bulk density than Trial 6.

Example 2: Post-Coated CER/Thermoplastic Composites

[0084] Exemplary post-coat compositions were prepared using different chemistries and used to post-coat CER tows. The exemplary tows were 800 tex and comprised 10 micron glass fibers having an 18% CNS loading. The post-coated CER tows were then chopped and compounded into various matrix materials to form CER composites. Each composite was about 0.125 inches thick and the EMI shielding Effectiveness (EMI SE) was measured according to ASTM 4935. The EMI SE listed below is an average from the frequency range of 0.5 to 2 GHz. The particular post-coat formulations and matrix materials used are listed below in Table 2.

Table 2. Post-Coated CER Composites.

17)- Nonionic 87% A- 1 100; 13% 14% 0.25 High density 27 5% 166E polygamma- PE

ethylene aminopropyltri

emulsion ethoxysilane

18)- None None High 47 5% No Density PE

post- coat

[0085] The EMI SE of the CER composites listed above correlates to the overall dispersion of the CNS throughout the thermoplastic material. The higher the EMI SE, the better dispersion achieved by the CNS in the composite. As shown above, Trials 9-10 include post- coated CER composites in polyamide 6,6. The post-coat of Trial 9 comprises an aqueous polyamide dispersion film former and an aminopropyl methyldiethoxy silane coupling agent. The post-coat of Trial 10 includes a non-ionic polypropylene emulsion film former and an N- (-aminoethyl)--aminopropylmethyldimethoxysilane coupling agent. As illustrated in the above table, each composite demonstrates EMI SE that is comparable to that of an un-post- coated CER composite in PA-6,6 (Trial 11). Accordingly, the post-coat compositions in Trials 9 and 10 are believed to maintain the dispersion ability of un-coated chopped strands.

[0086] Trials 12-13 comprise post-coated CER composites formed with polypropylene. The post-coat composition of Trial 12 included an aqueous polyurethane solution and a gamma - Aminopropyltriethoxysilane coupling agent. The post-coat composition of Trial 13 included a non-ionic propylene emulsion and an N-(-aminoethyl)~aminopropylmethyldimethoxysilane coupling agent. As shown in Table 2, although the post-coat of Trial 12 resulted in better bulk density, the resulting CER/polypropylene composite displayed low EMI SE as compared with the un-post-coated CER/polypropylene composite (Trial 14), which indicates that the CER chopped strands post-coated with the composition of of Trial 12 do not disperse as thoroughly as uncoated CER chopped strands. However, those composites formed with the post-coat composition of Trial 13 illustrated EMI SE comparable to that of an un-coated CER composite.

[0087] The post-coated CER composites of Trials 15-17 were formed using a high density polyethylene matrix material. Trial 15 was formed using a post-coat composition comprising an aqueous polyurethane solution film former and a gamma - aminopropyltriethoxysilane coupling agent. Trial 16 was formed using a nonionic polypropylene emulsion film former and an N-(-aminoethyl)-aminopropylmethyldimethoxysilane coupling agent. Finally, Trial 17 was formed using a non-ionic polyethylene emulsion film former and a gamma - aminopropyltriethoxysilane coupling agent. As shown in Table 2, each of Trials 15-17 demonstrate comparable bulk density, although only Trial 16 shows comparable EMI SE to that of the un-coated CER/high density polyethylene composite (Trial 18). Trial 15 demonstrated slightly better shielding results than Trial 17, which indicates that, since the post-coat compositions included the same silane, a post-coat composition comprising an aqueous polyurethane film former is believe to achieve better dispersion in high density polyethylene than that with a non-ionic polyethylene film former.

Example 3 : Dispersion Measurement

[0088] Exemplary post-coat compositions were prepared using different chemistries and used to post-coat CER tows. The exemplary tows were 800 tex and comprised 10 micron glass fibers having an 18% CNS loading. The post-coated CER tows were then chopped and injection molded with a polyamide 6,6 material to form a 6" x 6" x 1/8" composite panel. Three exemplary panels were prepared. The exemplary panels were tested for dispersion performance using the Aggregate Measurement Technique, which is described below.

[0089] The first panel was formed using uncoated CER chopped strands. Each of the remaining two panels included post-coated CER chopped strands. The particular post-coat compositions used are displayed below in Table 3.

Table 3. Post-Coated CER Composites

[0090] A 35 mm diameter piece was cored from each sample at the same location on the composite and the samples were polished to a 6 micron diamond finish. Approximately 1 mm portion of the top surface was removed from each sample and these portions were analyzed using reflected light stereoscope. The percentage in each portion that was covered by CER fiber aggregates larger than 175 micrometers in diameter were recorded. Additionally, the shielding effectiveness of each sample was measured according to ASTM D4935 on 0.125 inch thick injection molded parts at a frequency between 0.5 and 2 GHz. The results are listed in Table 3, above.

[0091] As shown in the Table, the composite formed using uncoated CER chopped strands demonstrated about 4% CER fiber aggregates and an EMI shielding effectiveness of 48 dB (Figure 9). Similarly, the composite formed using CER chopped strands that had been post- coated with the 154E post-coat composition similarly demonstrated 4% CER fiber aggregates and an improved EMI shielding effectiveness of 48 dB (Figure 11). However, the composite formed using CER chopped strands post-coated with the 162A post-coat composition demonstrated a higher percentage of CER fiber aggregates, at 13% and demonstrated low EMI shielding effectiveness at 34 dB (Figure 10). Therefore, the particular make up of the post-coat composition is important for achieving dispersion comparable to that achieved by non-post-coated CER chopped strands and particularly, a CER fiber aggregate percentage of less than 10%.

[0092] The general inventive concepts have been described above both generically and with regard to various exemplary embodiments. Although the general inventive concepts have been set forth in what is believed to be exemplary illustrative embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The general inventive concepts are not otherwise limited, except for the recitation of the claims set forth below.

Claims

CLAIMS:

1. A post-coated carbon enhanced reinforcement ("CER") chopped strand comprising: a CER chopped strand, wherein said CER chopped strand includes at least one reinforcement fiber having a plurality of carbon nanostructures ("CNSs") disposed thereon, said CNSs extending from said at least one reinforcement fiber; and

a post-coat composition substantially coating said CER chopped strand, forming a post-coated CER chopped strand, wherein said post-coated CER chopped strand has a bulk density of about 0.2 to about 0.5 g/ml.

2. The post-coated CER chopped strand of claim 1, wherein said chopped strand has a bulk density from about 0.25 to about 0.4 g/ml.

3. The post-coated CER chopped strand of claim 1, wherein said chopped strand has a CNS loading of about 10 to about 30 weight %.

4. The post-coated CER chopped strand of claim 3, wherein said chopped strand has a CNS loading of about 15 to about 25 weight %.

5. The post-coated CER chopped strand of claim 1, wherein said reinforcement fiber comprises one or more of glass, carbon, ceramic, and polymer.

6. The post-coated CER chopped strand of claim 1, wherein said post-coat composition comprises a solids content of about 0.5 weight % to about 30.0 weight %.

7. The post-coated CER chopped strand of claim 6, wherein said post-coat composition comprises a solids content of about 5.0 weight % to about 20 weight %

8. The post-coated CER chopped strand of claim 1, wherein said post-coat composition comprises one or more of film formers, coupling agents, viscosity modifiers, lubricants, antioxidants, surfactants, and plasticizers.

9. The CER chopped strand of claim 5, wherein said post-coat composition comprises a film former that comprises one or more of waxes, polyethylene glycols, polypropylene glycols, polycaprolactones, glycidyl ethers, epoxy resins, polyurethanes, polyester alkyds, amic acid, propylene glycol fumarate, propoxylated bisphenol-A-maleate, propoxylated allyl alcohol maleate, polyvinyl acetates, olefins, maleated polypropylene, and low molecular weight polyesters.

10. The CER chopped strand of claim 9, wherein said film former comprises at least one of a polyurethane and maleated polypropylene.

11. The CER chopped strand of claim 8, wherein said post-coat composition comprises a coupling agent that comprises one or more of alcohols, amines, esters, ethers, hydrocarbons, siloxanes, silazanes, silanes, lactams, lactones, anhydrides, carbenes, nitrenes, orthoesters, imides, enamines, imines, amides, imides, and functionalized olefins.

12. The CER chopped strand of claim 8, wherein said coupling agent comprise a organosilane.

13. The CER chopped strand of claim 5, wherein said post-coat composition comprises about 70 to about 99 weight % film former, about 1 to about 30 weight % coupling agent and about 0 to about 20 weight % of additives.

14. A CER/matrix material composite comprising:

a plurality of post-coated CER chopped strands, each CER chopped strand comprising:

a CER chopped strand, wherein said CER chopped strand include at least one reinforcement fiber having a plurality of CNSs disposed thereon, said CNSs extending from said at least one reinforcement fiber; and

a post-coat composition substantially coating said CER chopped strand, forming a post-coated CER chopped strand, wherein said post-coated CER chopped strand has a bulk density of about 0.2 to about 0.5 g/ml; and

a matrix material.

15. The composite of claim 14, wherein the composite includes about 10 to about 40 weight % CER chopped strand loading.

16. The composite of claim 14, wherein said composite includes about 1 to about 20 weight % CNS loading.

17. The composite of claim 16, wherein said composite has an EMI shielding efficiency between about 30 and about 100 dB over a frequency range of 50-2000 MHz.

18. The composite of claim 16, wherein said composite has an aggregate percentage of less than 10%.

19. The composite of claim 16, wherein said composite has a resistivity of between about lO^^'lO' oms+cm.

20. The composite of claim 14, wherein said post-coat composition comprises a film former with a softening temperature less than the processing temperature of said matrix material.

21. The composite of claim 14, wherein said matrix material comprises one or more of acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polycarbonate/acrylonitrile butadiene styrene (PC/ ABS), polysulfones, polystyrene, polyamides, polyethylenimine (PEI), polycarbonates, polyphenylene oxides, polysulfides, polyether ether ketones (PEEK), poly ether ketone (PEK), polyphenylene sulfide (PPS), polyurethane (PU), polyether sulfones, polyamide-imides, polyetherimides, polyimides, polyarylates, polyphthalamide, acrylic styrene acrylonitrile, polyphenylene ether, polypropylene (PP), polyolefin, polyester, rubber (SBR), butadiene nitrile rubber (BNR), ethylene propylene diene monomer rubber (EPDM), fluoropolymer (FP), liquid crystalline polyester, and other thermoplastics and alloys of thermoplastics.

22. A process for forming a post-coated CER chopped strand, said process comprising: forming at least one CER tow by growing a plurality of CNSs on one or more reinforcement fibers, wherein said CNSs extend radially from said one or more reinforcement fibers;

coating said CER tow with a post-coat composition, whereby coating said CER tow condenses said plurality of CNS on said reinforcement fiber forming a post-coated CER tow; chopping said post-coated CER tow forming post-coated CER chopped strand, wherein said post-coated CER chopped strand has a bulk density of about 0.2 to about 0.5 g/ml.

23. The process of claim 22, further including pulling said post-coated CER tow through one or more stripper dies to further condense the post-coated CER tow and remove excess moisture.

24. The process of claim 22, further including drying the post-coated CER tow prior to chopping.

25. The process of claim 24, wherein said drying is performed by an in-line drying oven.

26. The process of claim 24, wherein prior to chopping, said post-coated CER tow is dried to a moisture content of about 1 weight % to about 50 weight %.

27. The process of claim 22, further including mixing the post-coated CER chopped strands with a matrix material to form a CER/matrix material composite.

28. The process of claim 27, wherein said post-coat composition includes a film former with a softening temperature less than the processing temperature of said matrix material.

29. The process of claim 27, wherein said matrix material comprises a thermoplastic matrix material.

30. The process of claim 29, wherein the thermoplastic comprises one or more of acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), polysulfones, polyamides, polystyrene, polyethylenimine (PEI), polycarbonates, polyphenylene oxides, polysulfides, polyether ether ketones (PEEK), poly ether ketone (PEK), polyphenylene sulfide (PPS), polyurethane (PU), polyether sulfones, polyamide-imides, polyetherimides, polyimides, polyarylates, polyphthalamide, acrylic styrene acrylonitrile, polyphenylene ether, polypropylene (PP), polyolefin, polyester, rubber (SBR), butadiene nitrile rubber (BNR), ethylene propylene diene monomer rubber (EPDM), fluoropolymer (FP), liquid crystalline polyester, and other thermoplastics and alloys of thermoplastics.

31. An EMI shielding article formed from the process of claim 27, wherein composite has an EMI shielding efficiency between about 30 and about 100 dB over a frequency range of 50-2000 MHz.