A PROCESS FOR PRODUCING POLYMER FIBER HAVING AT LEAST ONE ADDITIVE, AND CARBON FIBERS MADE THEREFROM

Cross Reference to Related Applications

The present application claims priority to U.S. provisional application No. 63/037279, filed June 10, 2020, the entire contents of which is hereby incorporated by reference.

Field of the Invention

The present disclosure relates generally to a process for producing polymer fibers comprising as least one additive, typically an additive that is insoluble in the polymer solution from which it is made. The present disclosure also relates to carbon fibers, typically multifunctional carbon fibers, produced by such process.

Background

Carbon fibers have been used in a wide variety of applications because of their desirable properties, such as high strength and stiffness, high chemical resistance and low thermal expansion. For example, carbon fibers can be formed into a structural part that combines high strength and high stiffness, while having a weight that is significantly lighter than a metal component of equivalent properties. Increasingly, carbon fibers are being used as structural components in composite materials for aerospace and automotive applications, among others. In particular, composite materials have been developed wherein carbon fibers serve as a reinforcing material in a resin or ceramic matrix.

Over 90% of carbon fibers are derived from polyacrylonitrile (PAN)-based precursors. The process for PAN conversion to carbon fiber consists of solvent spinning (solution spinning), oxidation and stabilization, and then carbonization. While the main use for carbon fiber is derived from its high strength to weight ratio and its utility for applications that are weight sensitive, there are many reasons for adding foreign particles or chemical reagents to the fiber for giving supplemental benefits to the properties such as magnetic stimuli responsiveness, optical and electrical properties, catalytic behavior, capacitor and fuel cell capabilities, hydrogen storage capability, electromagnetic properties, antimicrobial properties, or process aids/template assistance for downstream manufacturing. For example, iron oxide may be added at small concentrations to give magnetic responsiveness, silver at ppm levels may be added to provide antimicrobial applications useful in the medical field, and metal oxides, such as nickel oxide, may be added to provide catalytic behavior.

Traditionally, the addition of insoluble chemicals, solid organic compounds, or inorganic materials to PAN polymer fibers has been achieved by addition of the said material to the PAN polymer solution prior to spinning. The additive is then encapsulated by the coagulation process into the fiber structure. However, this process is not commercially viable due to difficulties in filtration of the dope through spinning and also causes issues in mechanical performance for the fiber (in stretching or in application post-carbonization).

Thus, there is an ongoing need for the development of continuous processes for producing polymer fibers that allow penetration of additive materials into the fiber structure with mitigated impact on mechanical properties of the fiber made and, subsequently, carbon fiber made therefrom. Herein, a new strategy for the production of polymer fibers and carbon fibers made therefrom that would address one or more of the aforementioned disadvantages is described.

Summary of the Invention

In a first aspect, the present disclosure relates to a process for producing polymer fiber comprising at least one additive, the process comprising: a) spinning a polymer solution to form coagulated polymer fiber; b) drawing the coagulated polymer fiber through one or more draw and wash baths, resulting in drawn polymer fiber that are substantially free of solvent; and c) optionally, applying a size to the drawn polymer fiber; wherein the at least one additive is insoluble in the polymer solution and is present in at least one of the steps a) to c); thereby producing the polymer fiber comprising the at least one additive.

In a second aspect, the present disclosure relates to a process for producing carbon fiber, the process comprising:

(i) producing a polymer fiber comprising at least one additive according to the process according to any one of claims 1-17;

(ii) oxidizing the polymer fiber produced in step (i) to form stabilized carbon fiber precursor fibers and then carbonizing the stabilized carbon fiber precursor fiber, thereby producing the carbon fiber.

In a third aspect, the present disclosure relates to a composite material comprising the carbon fiber produced according to the process described herein; and a matrix resin.

Detailed Description

As used herein, the terms “a”, “an”, or “the” means “one or more” or “at least one” and may be used interchangeably, unless otherwise stated.

As used herein, the term “and/or” used in a phrase in the form of “A and/or B” means A alone, B alone, or A and B together.

As used herein, the term “comprises” includes “consists essentially of” and “consists of.” The term “comprising” includes “consisting essentially of” and “consisting of.”

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this specification pertains. As used herein, and unless otherwise indicated, the term “about” or “approximately” means an acceptable error for a particular value as determined by one of ordinary skill in the art, which depends in part on how the value is measured or determined.

In certain embodiments, the term “about” or “approximately” means within 1 , 2, 3, or 4 standard deviations. In certain embodiments, the term “about” or “approximately” means within 50%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.05% of a given value or range.

Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10; that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations.

Throughout the present disclosure, various publications may be incorporated by reference. Should the meaning of any language in such publications incorporated by reference conflict with the meaning of the language of the present disclosure, the meaning of the language of the present disclosure shall take precedence, unless otherwise indicated.

The first aspect of the present disclosure relates to a process for producing polymer fiber comprising at least one additive, the process comprising: a) spinning a polymer solution to form coagulated polymer fiber; b) drawing the coagulated polymer fiber through one or more draw and wash baths, resulting in drawn polymer fiber that are substantially free of solvent; and c) optionally, applying a size to the drawn polymer fiber; wherein the at least one additive is insoluble in the polymer solution and is present in at least one of the steps a) to c); thereby producing the polymer fiber comprising the at least one additive.

The polymer solution may be prepared according to methods known to those of ordinary skill in the art. For example, the polymer, typically a polyacrylonitrile-based (PAN) polymer, can be made by any polymerization method, including, but not limited to, solution polymerization, dispersion polymerization, precipitation polymerization, suspension polymerization, emulsion polymerization, and variations thereof.

One suitable method comprises mixing acrylonitrile (AN) monomer and one or more co-monomers in a solvent, forming a solution. The solution is heated to a temperature above room temperature (i.e. , greater than 25 °C), for example, to a temperature of about 40 °C to about 85 °C. After heating, an initiator is added to the solution to initiate the polymerization reaction. Once polymerization is completed, unreacted AN monomers are stripped off (e.g., by de-aeration under high vacuum) and the resulting PAN polymer solution is cooled down. At this stage, the polymer is in a solution, or dope, form. Thus, in an embodiment, the polymer is formed in a medium, typically one or more solvents, in which the polymer is soluble to form a solution.

In another suitable method, AN monomer and one or more co-monomers may be polymerized in a medium, typically aqueous medium, in which the resulting polymer is sparingly soluble or non-soluble. In this manner, the resulting polymer would form a heterogenous mixture with the medium. The resulting polymer is then filtered and dried. To prepare the spinning solution by this method, the isolated polymer, typically in the form a powder, can then be dissolved in one or more solvents to form the spinning solution. Thus, in an embodiment, the polymer is formed in a medium, typically aqueous medium, in which the polymer is sparingly soluble or non-soluble to form a mixture, isolated, and then dissolved in one or more solvents to form the polymer solution. The polymer may be made by polymerizing a formulation comprising acrylonitrile and less than or equal to 20 %, typically less than or equal to 10 %, more typically less than or equal to 5 %, by weight of co-monomer, relative to the weight of the formulation.

In an embodiment, the formulation comprises greater than or equal to 90 % acrylonitrile, less than or equal to 5 % co-monomer, and less than or equal to 1 % initiator, by weight relative to the total weight of the components. A sufficient amount of solvent to form a solution containing at least 10 wt % of final polymer, typically 16 wt % to 28 wt % of final polymer, more typically 19 wt % to 24 wt %, is used.

Examples of suitable solvents include, but are not limited to, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), dimethyl acetamide (DMAc), ethylene carbonate (EC), zinc chloride (ZnCl2)/water and sodium thiocyanate (NaSCN)/water.

Examples of suitable comonomers include, but are not limited to, vinyl-based acids, such as methacrylic acid (MAA), acrylic acid (AA), and itaconic acid (ITA); vinyl- based esters, such as methacrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), methyl methacrylate (MMA), ethyl methacrylate (EMA), propyl methacrylate, butyl methacrylate, b-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, 2- ethylhexylacrylate, isopropyl acetate, vinyl acetate (VA), and vinyl propionate; vinyl amides, such as vinyl imidazole (VIM), acrylamide (AAm), and diacetone acrylamide (DAAm); vinyl halides, such as allyl chloride, vinyl bromide, vinyl chloride and vinylidene chloride; ammonium salts of vinyl compounds and sodium salts of sulfonic acids, such as sodium vinyl sulfonate, sodium p-styrene sulfonate (SSS), sodium methallyl sulfonate (SMS), and sodium-2-acrylamido-2-methyl propane sulfonate (SAMPS), among others.

In an embodiment, the polymer is made by polymerizing acrylonitrile with co monomers selected from the group consisting of methacrylic acid (MAA), acrylic acid (AA), itaconic acid (ITA), vinyl-based esters, typically, methacrylate (MA), methyl methacrylate (MMA), vinyl acetate (VA), ethyl acrylate (EA), butyl acrylate (BA), ethyl methacrylate (EMA); and other vinyl derivatives, typically, vinyl imidazole (VIM), acrylamide (AAm), and diacetone acrylamide (DAAm); and mixtures thereof.

In another embodiment, the polymer is made by polymerizing acrylonitrile with co monomers selected from the group consisting of methacrylic acid, methyl acrylate, and mixtures thereof.

Suitable initiators (or catalysts), typically sources of free radicals, for the polymerization include, but are not limited to, azo-based compounds, such as azo- bisisobutyronitrile (AIBN), azobiscyanovaleric acid (ACVA), and 2,2’-azobis-(2,4- dimethyl) valeronitrile (ABVN), among others.

Another suitable source of free radicals include redox initiators, which are typically a mixture of at least one oxidant and at least one reducing agent.

Suitable oxidants include, but are not limited to, hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide, t-butyl-peroxyacetate, t-butyl- peroxybenzoate, t-butylperoxyoctoate, t-butyl peroxy neodecanoate, t- butylperoxyisobutarate, lauroyl peroxide, t-amyl peroxy pivalate, t-butyl peroxy pivalate, dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide (TBPO), diisopropyl peroxydicarbonate (IPP), and the like, as well as persulfates, such as, for example, sodium persulfate, potassium persulfate, ammonium persulfate, and the like, or potassium bromate.

Suitable reducing agents that may be included in the redox system, include, but are not limited to, bicarbonates, such as sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate, sodium formaldehyde sulfoxylate, ascorbic acid, erythorbic acid, sulfite, bisulfite or metasulfite (typically the sulfites, bisulfites or metasulfites of alkali metals), nitrilotrispropionamide, tertiary amines, and ethanolamines. Typically, suitable oxidants and reducing agents are water-soluble.

The polymer solution is then subjected to a spinning step to form coagulated polymer fiber. Typically, this step comprises spinning the polymer solution in or into a coagulation bath. The polymer solution (i.e. , spin “dope”) may be subjected to conventional wet spinning and/or air-gap spinning after removing air bubbles by vacuum. The spin dope can have a polymer concentration of at least 10 wt %, typically from about 16 wt % to about 28 wt % by weight, more typically from about 19 wt % to about 24 wt %, based on total weight of the solution. In wet spinning, the dope is filtered and extruded through holes of a spinneret (typically made of metal) into a liquid coagulation bath for the polymer to form filaments. The spinneret holes determine the desired filament count of the fiber (e.g., 3,000 holes for 3K carbon fiber). In air-gap spinning, a vertical air gap of 1 to 50 mm, typically 2 to 10 mm, is provided between the spinneret and the coagulating bath. In this spinning method, the polymer solution is filtered and extruded in the air from the spinneret and then extruded filaments are coagulated in a coagulating bath.

The coagulation liquid used in the process is a mixture of solvent and non-solvent. Water or alcohol is typically used as the non-solvent. Suitable solvents include the solvents described herein. In an embodiment, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, or mixtures thereof, is used as solvent. In another embodiment, dimethyl sulfoxide is used as solvent. The ratio of solvent and non solvent, and bath temperature are not particularly limited and may be adjusted according to known methods to achieve the desired solidification rate of the extruded nascent filaments in coagulation. However, the coagulation bath typically comprises 40 wt% to 85 wt% of one or more solvents, the balance being non-solvent, such as water or alcohol. In an embodiment, the coagulation bath comprises 40 wt% to 70 wt% of one or more solvents, the balance being non-solvent. In another embodiment, the coagulation bath comprises 50 wt% to 85 wt% of one or more solvents, the balance being non-solvent.

Typically, the temperature of the the coagulation bath is from 0 °C to 80 °C. In an embodiment, the temperature of the coagulation bath is from 30 °C to 80 °C. In another embodiment, the temperature of the coagulation bath is from 0 °C to 20 °C.

In an embodiment, the at least one additive is present in the coagulation bath and the at least one additive is insoluble in the coagulation bath. As used herein, the term “insoluble” when used to describe a material means that less than 5% by weight, typically less than 1 % by weight, more typically less than 0.5% by weight, of the material, relative to the weight of a particular solvent or blend of solvents, is dissolved in the said solvent or blend of solvents. In some cases, no detectable amount of the material is dissolved in the said solvent or blend of solvents, such methods of detection being analytical techniques known to the ordinarily-skilled artisan, such as, for example, gas or liquid chromatography, spectrophotometry, optical microscopy, and the like. Thus, the insoluble material and the solvent or blend of solvents are present as a heterogenous mixture.

In an embodiment, the at least one additive is present in the coagulation bath in an amount of less than or equal to 15%; less than or equal to 8%; than or equal to 4%; less than or equal to 2%; or less than or equal to 1 %, by weight relative to the weight of the coagulation bath.

Thus, when the at least one additive is present in the coagulation bath, the extruded nascent filaments coagulates and solidifies into fibers while in the presence of the additive.

According to the process of the present disclosure, the coagulated polymer fiber formed are in the coagulation bath for less than or equal to 15 minutes, typically less than or equal to 5 minutes, more typically less than or equal to 1 minute, for example, less than or equal to 30 seconds.

The drawing of the coagulated polymer fiber is conducted by conveying the said fibers through one or more draw and wash baths, for example, by rollers. The coagulated polymer fibers are conveyed through one or more wash baths to remove any excess solvent and stretched in hot (e.g., 40° C. to 100° C.) water baths to impart molecular orientation to the filaments as the first step of controlling fiber diameter. The result is drawn polymer fiber that are substantially free of solvent. According to the process of the present disclosure, the at least one additive may be present in one or more of the draw and wash baths in step b) and the at least one additive is insoluble in the said draw and wash baths.

In an embodiment, the at least one additive is present in one or more of the draw and wash baths in an amount of less than or equal to 15%; less than or equal to 8%; than or equal to 4%; less than or equal to 2%; or less than or equal to 1%, by weight relative to the weight of the one or more draw and wash baths.

Generally, the drawn polymer fibers are in the one or more draw and wash baths for less than or equal to 15 minutes, typically less than or equal to 5 minutes, more typically less than or equal to 1 minute, for example, less than or equal to 30 seconds.

Step b) of the process may further comprise drying the drawn polymer fibers that are substantially free of solvent, for example, on drying rolls. The drying rolls can be composed of a plurality of rotatable rolls arranged in series and in serpentine configuration over which the filaments pass sequentially from roll to roll and under sufficient tension to provide filaments stretch or relaxation on the rolls. At least some of the rolls are heated by pressurized steam, which is circulated internally or through the rolls, or electrical heating elements inside of the rolls. Finishing oil can be applied onto the stretched fibers prior to drying in order to prevent the filaments from sticking to each other in downstream processes.

Optionally, the process may comprise a step c) of applying a size to the drawn polymer fiber.

In an embodiment, the size is applied to the drawn polymer fiber by conveying the drawn polymer fiber through a sizing bath, sometimes called a spin finish. The sizing bath contains a liquid coating material, typically a process oil, such as a silicone dispersion. In another embodiment, the at least one additive is present in the sizing bath and the at least one additive is insoluble in the sizing bath.

In yet another embodiment, the at least one additive is present in the sizing bath in an amount of less than or equal to 15%; less than or equal to 8%; than or equal to 4%; less than or equal to 2%; or less than or equal to 1 %, by weight relative to the weight of the sizing bath.

In an embodiment, the process is conducted continuously. As used herein, a process “conducted continuously” refers to a process in which the fiber is conveyed through one or more processing steps a single work unit at a time without any breaks in time, substance, or sequence. This is in contrast to a batch process, which would be understood as being a process that comprises a sequence of one or more steps that are performed in a defined order and in which a finite quantity of material is treated or produced at the end of the sequence, which must be repeated in order to treat or produce another batch of material.

The present disclosure contemplates processes used in the production of multifunctional fibers, including polymer fiber and carbon fiber. As used herein, the term “multifunctional” means that such fiber possesses one or more properties or functions in addition to the mechanical load bearing component of a given application, which may also be enhanced by the inclusion of a suitable additive.

In accordance with the present disclosure, the at least one additive provides one or more of the following properties:

- magnetic stimuli responsiveness,

- optical properties,

- electrical conductivity,

- electromagnetic properties,

- ionic conductivity,

- catalytic behavior,

- antimicrobial or biocidal properties,

- shape memory, - gas absorption/adsorption properties,

- mechanical properties,

- aid for downstream manufacturing.

The present disclosure also contemplates chemical reactivity as a property that may be added to the polymer fibers made according to the process described herein. In such an embodiment, one or more types of additive may be incorporated into the fiber, typically at different steps selected from steps a), b), and c), and the additives may be reactive with each other (in the case when more than one type of additive is used), with the polymer of the fiber, or with the process oil used in the spin finish.

Suitable additives may be organic compounds or inorganic materials. Suitable additives may include, but are not limited to, metals and metal-containing compounds; carbonaceous materials; and silicon and silicon-containing compounds.

Exemplary additives include, but are not limited to, additives selected from the group consisting of aluminum (Al), indium (In), tin (Sn), and alloys and derivatives thereof; transition metals and transition metal compounds, typically titanium (Ti), chromium (Cr), iron (Fe), nickel (Ni), such as nickel oxides, copper (Cu), zinc (Zn), palladium (Pd), silver (Ag), cadmium (Cd), iridium (Ir), platinum (Pt), gold (Au), and alloys and derivatives thereof; carbonaceous materials, such as carbon nanotubes; and silicon and derivatives thereof.

In an embodiment, the at least one additive is in nanoparticle form, typically having an average diameter of less than or equal to 2000 nm, less than or equal to 500 nm, less than or equal to 250 nm, less than or equal to 100 nm, or less than or equal to 50 nm.

The process described herein is advantageous for incorporation of one or more additives that is/are insoluble in the polymer solution that is used to form a polymer fiber suitable for use in carbon fiber manufacturing. The additive may also be insoluble in one or more of the baths used, such as the coagulation bath, the one or more draw and wash baths, or the sizing bath. In some embodiments, an additive may be present in any two of step a), step b), and optional step c). For example, an additive may be present in step a) and step b); in step b) and optional step c), or step a) and optional step c). In other embodiments, an additive may be present in step a), step b), and optional step c).

In the case when more than one step contains the use of a suitable additive as described herein, the additive may be identical or different in each step. For example, the additive used in step a) may be identical to or different from the additive used in step b) in the case when an additive is present in step a) and step b).

In the second aspect, the present disclosure relates to a process for producing carbon fiber, the process comprising:

(i) producing a polymer fiber comprising at least one additive according to the process described herein;

(ii) oxidizing the polymer fiber produced in step (i) to form stabilized carbon fiber precursor fibers and then carbonizing the stabilized carbon fiber precursor fiber, thereby producing the carbon fiber.

The polymer fiber comprising at least one additive may be oxidized to form stabilized carbon fiber precursor fibers and, subsequently, the stabilized carbon fiber precursor fiber are carbonized to produce carbon fibers.

During the oxidation stage, the polymer fiber comprising at least one additive are fed under tension through one or more specialized ovens, each having a temperature from 150 to 300 °C, typically from 200 to 280 °C, more typically from 220 to 270 °C. Fleated air is fed into each of the ovens. The polymer fibers comprising at least one additive are conveyed through the one or more ovens at a speed of from 4 to 100 fpm, typically from 30 to 75 fpm, more typically from 50 to 70 fpm.

The oxidation process combines oxygen molecules from the air with the fiber and causes the polymer chains to start crosslinking, thereby increasing the fiber density to 1.3 g/cm ³ to 1.4 g/cm ³ . In the oxidization process, the tension applied to fiber is generally to control the fiber drawn or shrunk at a stretch ratio of 0.8 to 1.35, typically 1.0 to 1.2. When the stretch ratio is 1 , there is no stretch. And when the stretch ratio is greater than 1 , the applied tension causes the fiber to be stretched. Such oxidized PAN fiber has an infusible ladder aromatic molecular structure and it is ready for carbonization treatment.

Carbonization results in the crystallization of carbon molecules and consequently produces a finished carbon fiber that has more than 90 percent carbon content. Carbonization of the oxidized, or stabilized, carbon fiber precursor fibers occurs in an inert (oxygen-free) atmosphere, typically nitrogen atmosphere, inside one or more specially designed furnaces. The oxidized carbon fiber precursor fibers are passed through one or more ovens each heated to a temperature of from 300 °C to 1650 °C, typically from 1100 °C to 1450 °C.

In an embodiment, the oxidized fiber is passed through a pre-carbonization furnace that subjects the fiber to a heating temperature of from about 300 °C to about 900 °C, typically about 350 °C to about 750 °C, while being exposed to an inert gas (e.g., nitrogen), followed by carbonization by passing the fiber through a furnace heated to a higher temperature of from about 700 °C to about 1650°C, typically about 800 °C to about 1450 °C, while being exposed to an inert gas. Fiber tensioning may be added throughout the precarbonization and carbonization processes. In pre carbonization, the applied fiber tension is sufficient to control the stretch ratio to be within the range of 0.9 to 1.2, typically 1.0 to 1.15. In carbonization, the tension used is sufficient to provide a stretch ratio of 0.9 to 1.05.

Adhesion between the matrix resin and carbon fiber is an important criterion in a carbon fiber-reinforced polymer composite. As such, during the manufacture of carbon fiber, surface treatment may be performed after oxidation and carbonization to enhance this adhesion.

Surface treatment may include pulling the carbonized fiber through an electrolytic bath containing an electrolyte, such as ammonium bicarbonate or sodium hypochlorite. The chemicals of the electrolytic bath etch or roughen the surface of the fiber, thereby increasing the surface area available for interfacial fiber/matrix bonding and adding reactive chemical groups.

Next, the carbon fiber may be subjected to sizing, where a size coating, e.g. epoxy- based coating, is applied onto the fiber. Sizing may be carried out by passing the fiber through a size bath containing a liquid coating material. Sizing protects the carbon fiber during handling and processing into intermediate forms, such as dry fabric and prepreg. Sizing also holds filaments together in individual tows to reduce fuzz, improve processability and increase interfacial shear strength between the fiber and the matrix resin.

Following sizing, the coated carbon fiber is dried and then wound onto a bobbin.

A person of ordinary skill in the art would understand that the processing conditions (including composition of the spin solution and coagulation bath, the amount of total baths, stretches, temperatures, and filament speeds) are correlated to provide filaments of a desired structure and denier.

In a third aspect, the present disclosure relates to a composite material comprising the carbon fiber produced according to the process described herein and a matrix resin.

Composite materials may be made by molding a preform comprising the carbon fiber produced according to the process described herein and infusing the preform with a thermosetting resin in a number of liquid-molding processes. Liquid-molding processes that may be used include, without limitation, vacuum-assisted resin transfer molding (VARTM), in which resin is infused into the preform using a vacuum-generated pressure differential. Another method is resin transfer molding (RTM), wherein resin is infused under pressure into the preform in a closed mold. A third method is resin film infusion (RFI), wherein a semi-solid resin is placed underneath or on top of the preform, appropriate tooling is located on the part, the part is bagged and then placed in an autoclave to melt and infuse the resin into the preform.

The matrix resin for impregnating or infusing the preforms described herein is a curable resin. “Curing” or “cure” in the present disclosure refers to the hardening of a polymeric material by the chemical cross-linking of the polymer chains. The term “curable” in reference to a composition means that the composition is capable of being subjected to conditions which will render the composition to a hardened or thermoset state. The matrix resin typically is a hardenable or thermoset resin containing one or more uncured thermoset resins or thermoplastic resin. Suitable thermoset resins include, but are not limited to, epoxy resins, oxetanes, imides (such as polyimide or bismaleimide), vinyl ester resins, cyanate ester resins, isocyanate-modified epoxy resins, phenolic resins, furanic resins, benzoxazines, formaldehyde condensate resins (such as with urea, melamine or phenol), polyesters, acrylics, hybrids, blends and combinations thereof. Suitable thermoplastic resins include, but are not limited to polyolefins, fluoropolymers, perfluorosulfonic acids, poly amid-imides, polyamides, polyesters, polyketones, polyphenylene sulfides, polyvinylidene chlorides, sulfone polymers, hybrids, blends and combinations thereof.

Suitable epoxy resins include glycidyl derivatives of aromatic diamine, aromatic mono primary amines, aminophenols, polyhydric phenols, polyhydric alcohols, polycarboxylic acids and non-glycidyl resins produced by peroxidation of olefinic double bonds. Examples of suitable epoxy resins include polyglycidyl ethers of the bisphenols, such as bisphenol A, bisphenol F, bisphenol S, bisphenol K and bisphenol Z; polyglycidyl ethers of cresol and phenol-based novolacs, glycidyl ethers of phenol-aldelyde adducts, glycidyl ethers of aliphatic dials, diglycidyl ether, diethylene glycol diglycidyl ether, aromatic epoxy resins, aliphatic polyglycidylethers, epoxidised olefins, brominated resins, aromatic glycidyl amines, heterocyclic glycidyl imidines and amides, glycidyl ethers, fluorinated epoxy resins, or combinations thereof. Specific examples are tetraglycidyl derivatives of 4,4'-diaminodiphenylmethane (TGDDM), resorcinol diglycidyl ether, triglycidyl-p-aminophenol, triglycidyl-m- aminophenol, bromobisphenol F diglycidyl ether, tetraglycidyl derivatives of diaminodiphenylmethane, trihydroxyphenyl methane triglycidyl ether, polyglycidylether of phenol-formaldehyde novolac, polyglycidylether of o-cresol novolac or tetraglycidyl ether of tetraphenylethane.

Suitable oxetane compounds, which are compounds that comprise at least one oxetano group per molecule, include compounds such as, for example, 3-ethyl-3[[(3- ethyloxetane-3-yl)methoxy]methyl]oxetane, oxetane-3-methanol, 3,3-bis- (hydroxymethyl) oxetane, 3-butyl-3-methyl oxetane, 3-methyl-3-oxetanemethanol, 3,3-dipropyl oxetane, and 3-ethyl-3-(hydroxymethyl) oxetane.

The curable matrix resin may optionally comprise one or more additives such as curing agents, curing catalysts, co-monomers, rheology control agents, tackifiers, inorganic or organic fillers, thermoplastic and/or elastomeric polymers as toughening agents, stabilizers, inhibitors, pigments, dyes, flame retardants, reactive diluents, UV absorbers and other additives well known to those of ordinary skill in the art for modifying the properties of the matrix resin before and/or after curing.

Examples of suitable curing agents include, but are not limited to, aromatic, aliphatic and alicyclic amines, or guanidine derivatives. Suitable aromatic amines include 4,4'-diaminodiphenyl sulphone ( 4,4'-DDS), and 3,3'diaminodiphenyl sulphone (3,3- DDS), 1 ,3-diaminobenzene, 1 ,4-diaminobenzene, 4,4'-diammodiphenylmethane, benzenediamine(BDA); Suitable aliphatic amines include ethylenediamine (EDA), 4,4'-methylenebis(2,6-diethylaniline) (M-DEA), m-xylenediamine (mXDA), diethylenetriamine (DETA), triethylenetetramine (TETA), trioxatridecanediamine (TTDA), polyoxypropylene diamine, and further homologues, alicyclic amines such as diaminocyclohexane (DACH), isophoronediamine (IPDA), 4,4' diamino dicyclohexyl methane (PACM), bisaminopropylpiperazine (BAPP), N- aminoethylpiperazine (N-AEP); Other suitable curing agents also include anhydrides, typically polycarboxylic anhydrides, such as nadic anhydride, methylnadic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, endomethylene-tetrahydrophtalic anhydride, pyromellitic dianhydride, chloroendic anhydride and trimellitic anhydride.

Still other curing agents are Lewis acid: Lewis base complexes. Suitable Lewis acid:Lewis base complexes include, for example, complexes of: BCh:amine complexes, BF3:amine complexes, such as BF3:monoethylamine, BF3:propylamine, BF3:isopropyl amine, BF3:benzyl amine, BF3:chlorobenzyl amine,

BF3:trimethylamine, BF3:pyridine, BF3:THF, AICh HF, AICl3:acetonitrile, and ZnCI ₂ :THF.

Additional curing agents are polyamides, polyamines, amidoamines, polyamidoamines, polycycloaliphatic, polyetheramide, imidazoles, dicyandiamide, substituted ureas and urones, hydrazines and silicones.

Urea based curing agents are the range of materials available under the commercial name DYHARD (marketed by Alzchem), and urea derivatives, such as the ones commercially available as UR200, UR300, UR400, UR600 and UR700. Urone accelerators include, for example, 4,4-methylene diphenylene bis(N,N-dimethyl urea) (available from Onmicure as U52 M).

When present, the total amount of curing agent is in the range of 1 wt % to 60 wt % of the resin composition. Typically, the curing agent is present in the range of 15 wt % to 50 wt %, more typically in the range of 20 wt % to 30 wt %.

Suitable toughening agents may include, but are not limited to, homopolymers or copolymers either alone or in combination of polyamides, copolyamides, polyimides, aramids, polyketones, polyetherimides (PEI), polyetherketones (PEK), polyetherketoneketone (PEKK), polyetheretherketones (PEEK), polyethersulfones (PES), polyetherethersulfones (PEES), polyesters, polyurethanes, polysulphones, polysulphides, polyphenylene oxide (PPO) and modified PPO, polyethylene oxide) (PEO) and polypropylene oxide, polystyrenes, polybutadienes, polyacrylates, polystyrene, polymethacrylates, polyacrylics, polyphenylsulfone, high performance hydrocarbon polymers, liquid crystal polymers, elastomers, segmented elastomers and core-shell particles.

Toughening particles or agents, when present, may be present in the range 0.1 wt % to 30 wt % of the resin composition. In an embodiment, the toughening particles or agents may be present in the range 10 wt % to 25 wt %. In another embodiment, the toughening particles or agents may be present in the range from 0.1 to 10 wt%. Suitable toughening particles or agents include, for example, Virantage VW10200 FRP, VW10300 FP and VW10700 FRP from Solvay, BASF Ultrason E2020 and Sumikaexcel 5003P from Sumitomo Chemicals.

The toughening particles or agents may be in the form of particles having a diameter larger than 20 microns to prevent them from being incorporated into the fiber layers. The size of the toughening particles or agents may be selected such that they are not filtered by the fiber reinforcement. Optionally, the composition may also comprise inorganic ceramic particles, microspheres, micro-balloons and clays.

The resin composition may also contain conductive particles such as the ones described in PCT International Publications WO 2013/141916, WO 2015/130368 and WO 2016/048885.

The mold for resin infusion may be a two-component, closed mold or a vacuum bag sealed, single-sided mold. Following infusion of the matrix resin in the mold, the mold is heated to cure the resin.

During heating, the resin reacts with itself to form crosslinks in the matrix of the composite material. After an initial period of heating, the resin gels. Upon gelling, the resin no longer flows, but rather behaves as a solid. After gel, the temperature or cure may be ramped up to a final temperature to complete the cure. The final cure temperature depends on the nature and properties of the thermosetting resin chosen. Thus, in a suitable method, the composite material is heated to a first temperature suitable to gel the matrix resin, after which the temperature is ramped up to a second temperature and held for a time at the second temperature to complete the cure.

Thus, a composite article is obtained by curing the composite material described herein.

The process according to the present disclosure and carbon fibers produced therefrom are further illustrated by the following non-limiting examples.

Examples

Example 1. Nickel oxide nano-additive

A solution of terpolymer including a comonomer containing a carboxylic acid functionality and a neutral monomer of molecular weight above 200,000 g/mol (12-15 wt. % solution) was used to produce the corresponding white fiber.

A spin run was started with wet spinning the PAN polymer solution with 500 filaments into a coagulation bath containing a mixture of water and DMSO, followed by a “gel stretch” (GS) bath (containing a lesser extent of DMSO at room temperature), a draw bath. The spin run included successive wash baths and draw baths of water. Following all of the wash and draw baths was a process oil application (“spin finish”, “SF”) and a set of drying rolls and finally a dancer arm for a winder.

The fiber was treated nickel oxide (NiO) nanoparticles (available from US Research Nanomaterials, Inc., 20 wt% in water, 18-nm nanoparticles) at three stages: during coagulation, during gel stretch, and during the spin finish. Nickel oxide dispersions were diluted to the target concentration of 1 wt% for the baths used at the specified stages, i.e. , the coagulation bath, the gel stretch bath, and the spin finish bath.

Unless otherwise stated, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed on the liquid samples to determine actual loading concentrations and on dipped precursor fibers to identify effects on thermal properties. During the course of the spin run, the concentration of NiO in the coagulation bath dropped from 0.4 wt.% to about 0.3 wt.% while concentration of NiO in the GS bath dropped from about 0.61 wt.% to about 0.55 wt.% before being intentionally emptied to about 0 wt.%.

It was observed that the dipped fibers exhibited a gray color change as they exited each bath. The fiber retained the gray color through the process and ends with faint gray tint.

Swelling studies were performed to determine the effect of NiO on the porosity and swelling ratio.

Generally, samples were taken from the specified bath and were centrifuged at 3000 rpm for 15 minutes to remove the adhered liquid from the filament surface. The collected samples were then submerged in a glass beaker/flask containing deionized water (DIW), and “washed” for a minimum of 15 minutes. This washing step was then repeated twice more with fresh DIW to ensure that the solvent had been removed. Once the final wash was completed, the sample was centrifuged again at 3,000 rpm for 15 minutes and weighed to obtain the W _a (after-wash) weight.

Samples were then placed in an air circulating oven at 110° C. for 3 hours.

Following drying, samples were removed from the oven and placed in a desiccator for a minimum of ten minutes. The dried and desiccated samples were re-weighed and the final weight recorded as Wf. The degree of swelling was then calculated using the following formula:

Degree of Swelling (%) = (W _a - W _f )x(100/W _f )

The polymer, in the absence of NiO in the coagulation bath, has a coagulation swelling of 191%. With NiO present in the coagulation bath, only an increase of 1% to 192% was observed, which demonstrates that the NiO has a negligible effect on the swelling. The gel stretch samples also showed no significant change compared to the control (216% swelling). The amount of nanoadditive pickup was quantified by ICP analysis of Ni content as each of the stages investigated and the results are summarized in Table 1 below.

Table 1.

The results are additive, or each successive stage results in a higher Ni content.

This suggests that the Ni does not wash out of the fiber through the many washing and drying stages. Furthermore, the amount of Ni increase appears to have diminishing returns where the greatest amount of Ni added was in the coagulation bath followed by gel stretch and, lastly, in spin finish. This is significant because it validates that the fiber has a greater propensity to incorporate nanomaterials at the earlier stages in the spinning process.

The final white fiber properties are also of interest due to the presence of the nanoadditive having a potentially detrimental effect on the thermal, morphological, and mechanical properties of such white fibers. However, analysis of the final white fiber showed no indication that the Ni additive had any adverse effect on the cyclization exotherm or the degradation profile in nitrogen. No adverse effects on the mechanical properties of the white fiber, such as elongation, tenacity, and modulus, were observed. If anything, the fibers treated with NiO showed enhanced degradation profiles compared with the baseline as they all demonstrate increased mass yield.

As described herein, the inventive process allows for the introduction of a beneficial additive, typically an additive that is insoluble in the polymer solution (“spin dope”) as well as insoluble in the various baths used in the formation of polymer white fiber, while mitigating problems associated with the actual manufacturing process, for example, filtration of the additive out of the spin dope during spinning, as well as impact on the properties, such as thermal, morphological, and mechanical properties, of the fiber made.

It would be apparent to a person of ordinary skill in that art that the conditions for conducting the inventive process described herein may be optimized based on the intended application and circumstances.