Melt blown and spun bond fabrication of non-woven carbon fiber fabric or web

Abstract

Disclosed examples generally relate to a method of making carbon fiber fabrics or webs by a spun bond approach comprising: (i) forming fibers by melt-extruding an asphaltene-based precursor material through a spinneret opening at a spinning temperature greater than about 200° C; (ii) drawing the fibers by airflow to reduce the diameter of the fibers; (iii) depositing the drawn fibers to form a fabric or a web; (iv) stabilizing and / or oxidizing the fabric or web, preferably by soaking the fabric or web in a nitric acid bath and stabilizing the fabric or web in air; and (v) carbonizing the fabric or web.

Description

MELT BLOWN AND SPUN BOND FABRICATION OF NON-WOVEN CARBON FIBER FABRIC OR WEB

[0001] This application claims priority to United States Provisional Patent Application No.63 / 752,051, filed on January 31, 2025, the entire contents of which are incorporated herein by reference.FIELD OF THE INVENTION

[0002] This disclosure relates to the fabrication of non-woven carbon fiber fabrics or webs using an asphaltene-based precursor material and a spun bond or a melt blown process.BACKGROUND

[0003] Fibers are generally fabricated by extruding precursor materials through a nozzle, often called a spinneret having many small openings, which may range from a single opening to thousands of openings. The precursor materials, usually in liquid phase, are extruded through the openings and are converted first to a rubber-fluid state and then solidified. This process of extrusion and solidification of endless filaments is known as spinning and may be grouped into four different categories: wet, dry, melt, and gel spinning.

[0004] Wet spinning uses fiber-forming substances that have been dissolved in a solvent. The spinnerets are submerged in a chemical bath and as the filaments emerge, they precipitate from solution and solidify. Because the solution is extruded directly into the precipitating liquid, this process for making fibers is called wet spinning. Polymer fibers, such as polyacrylonitrile (PAN) acrylic, rayon, aramid, modacrylic and spandex can be produced by this method. PAN wet spun fibers are useful to produce carbon fibers.

[0005] Dry spinning is also used for fiber-forming substances in solution. Instead of precipitating the polymer by dilution or chemical reaction, solidification is achieved by evaporating the solvent in a stream of air or inert gas. The filaments do not meet a precipitating liquid, eliminating the need for drying and easing solvent recovery. This process is used to produce polyacrylonitrile, acetate, triacetate, modacrylic, PBI, spandex, and rayon.

[0006] Electrospinning is a fiber production method that uses electrical force to draw charged threads of polymer solutions (solutions containing polymers) to produce fibers with diameters ranging from nanometers to micrometers. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. Electrospinning from molten precursors is also practiced which does not require the use of a solvent; this method ensures that no solvent can be carried over into the final product.

[0007] Melt spinning is a fiber-forming process where the precursor substance is melted for extrusion through the spinneret and then directly solidified by cooling. Conventionally, the fibers are wound on a spool rotated at a given speed. Those precursors that are of thermoplastic nature, such as pitch, nylon, olefin, polyester saran and sulfur, are melt-spinnable. Polyacrylonitrile (PAN) is not melt-spinnable because of the cyclization that stabilizes the polymers during heating before melting.

[0008] Gel spinning is a special process used to obtain high strength or other special fiber properties. The polymer is not in a true liquid state during extrusion. Not completely separated, as they would be in a true solution, the polymer chains are bound together at various points in liquid crystal form. This produces strong inter-chain forces in the resulting filaments that can significantly increase the tensile strength of the fibers. In addition, the liquid crystals are aligned along the fiber axis by the shear forces during extrusion. The filaments emerge with an unusually high degree of orientation relative to each other, furtherenhancing strength. The process can also be described as dry-wet spinning, since the filaments first pass through air and then are cooled further in a liquid bath. Some high-strength polyethylene and aramid fibers are produced by gel spinning.

[0009] Carbon fibers are conventionally produced by wet or dry spinning PAN. PAN based fibers cannot be melt spun because below 300°C, a cyclization reaction which occurs, and above 300°C the polymer melts. Consequently, PAN-based fibers are spun through a traditional spinning from a solution of PAN in the solvent usually less than 20-25%, which is required to be recovered.

[0010] Asphaltenes can be formed into precursor fibers either by a melt-spinning or wetspinning process. Melt-spinning produces precursor fibers by heating the precursors to temperatures about 30-40° C higher than their softening points and pressing them through nozzles of about 1.0-0.1 mm in diameter. Melt spinning an asphaltene-based precursor to produce carbon fibers is described in co-owned PCT International Patent Application No. PCT / CA2020 / 051403, the entire contents of which are incorporated herein by reference, where permitted. A wet spinning process fabricates precursor fibers at room temperature using a solution of asphaltenes dissolved in a solvent. The precursor fibers are formed after the solvent is removed.

[0011] The precursor fibers can then be stabilized and carbonized to form carbon fibers. Carbon fibers are usually considered to be anisotropic material with high strength measured in the fibrous length direction. The tensile properties in the direction of fibrous length, including tensile strength, tensile modulus and elongation before pulling to break are critical to the performance of carbon fibers that are used to make carbon-fiber reinforced composites.SUMMARY

[0012] This disclosure relates to methods of melt spinning of an asphaltene-based precursor material, comprising a melt blown and / or spun bond method to fabricate a non-woven fabric or web, which can then be carbonized to form a non-woven carbon fiber fabric or web. The carbon fiber fabric or web derived from an asphaltene-based precursor material comprises desirable characteristics in terms of productivity of carbon fiber fabrication and carbon fiber tensile strength and modulus.

[0013] In some embodiments, the carbon fiber fabric or web can be impregnated with a resin to produce a carbon fiber prepreg.

[0014] In some embodiments, a hydrocarbon feedstock is processed to produce an asphaltene-based precursor material with a desired softening point, preferably to increase the softening point. In some embodiments, a hydrocarbon feedstock is treated to increase its softening point using methods described in PCT International Application PCT / CA2021 / 000092, the entire contents of which are incorporated herein by reference, where permitted.

[0015] The precursor material is melt-extruded at a spinning temperature that is higher, preferably about 30° to 40° C higher, than the softening point of the material, at which point the material viscosity is suitable to produce the desired fibers.

[0016] In one aspect, disclosed is a process of producing a carbon fiber fabric or web comprising the steps of:(a) forming fibers by melt-extruding an asphaltene-based precursor material at a spinning temperature greater than about 200°C, 230°C, 250°C, or 280° C;(b) drawing the fibers by airflow to reduce the diameter of the fibers;(c) depositing the drawn fibers to form a fabric or a web;(d) stabilizing and / or oxidizing the fabric or web, preferably by soaking the fabric or web in a nitric acid bath and stabilizing the fabric or web in air; and(e) carbonizing the fabric or web.

[0017] In some embodiments, the precursor material is extruded at a flow rate of 0.05 to 0.5 g / min through each spinneret hole having an opening diameter of at least 0.2 mm, in a spun-bond process. The produced fibers are continuous fibers.

[0018] In some embodiments, the precursor material is extruded at a precursor flow rate of 0.001 to 0.05 g / min through each spinneret hole having a diameter of at least 0.2 mm, in a melt-blown process. The produced fibers are discrete fibers.

[0019] In some embodiments, step (a) of forming takes place at a temperature of about 200°C to 320°C, preferably at a temperature between about 280° C and 300° C.

[0020] In some embodiments, step (b) of drawing reduces said fibers’ diameter to about 1 / 10 to about 1 / 150 of the diameter of the spinneret opening.

[0021] In some embodiments, the spinneret opening has a diameter of about 0.2 mm or greater.

[0022] In some embodiments, the nitric acid bath has a nitric acid concentration ranging from 5 to 40%.

[0023] In some embodiments, the nitric acid soak is for a period ranging from 0.5 to 30 minutes.

[0024] In some embodiments, the fabric or web is stabilized in air at a temperature between about 200° C to 350° C, for a period of between 1 minute to about 2 hours.

[0025] In another broad aspect, there is provided a carbon fiber fabric or web formed by the above-noted method or process, comprising a carbon fiber having a minimum tensile strength of 3000 MPa.

[0026] In another broad aspect, there is provided a carbon fiber fabric or web formed by the above-noted process, comprising a carbon fiber having a minimum tensile strength of 2000 MPa.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the drawings, like elements are assigned like reference numerals. The drawings are not necessarily to scale, with the emphasis instead placed upon the principles of the present invention. Additionally, each of the embodiments depicted is but one of a number of possible arrangements utilizing the fundamental concepts of the present invention.

[0028] Figure 1 is a schematic overview of one embodiment of a process to produce carbon fiber fabrics or webs from an asphaltene-based precursor by spun bond approach.

[0029] Figure 2 shows a schematic of an exemplary melt-blown system, where the airflow is located beside the spinning head.

[0030] Figure 3 shows a schematic of an exemplary spun-bond system, where the airflow is located below the spinning head.DETAILED DESCRIPTION

[0031] The production of high-quality carbon fiber from an asphaltene-based precursor material is described in co-pending PCT International Application PCT / CA2024 / 051360, the entire contents of which are incorporated herein by reference, where permitted.

[0032] Embodiments disclosed herein modify that process by melt-spinning the asphaltene-based precursor material with a melt-blown or spun-bond approach to produce a precursor fabric or web, which is subsequently carbonized into a carbon fiber fabric or web. The carbon fiber fabric or web may then be graphitized and / or impregnated with a resin to form a prepreg.

[0033] Melt-spinning comprises a process whereby a molten thermoplastic polymer is extruded through a die or spinneret and elongated to form thin fibers. The process may also be referred to as melt-extrusion spinning.

[0034] Embodiments disclosed herein are not limited by the source of the hydrocarbon feedstock. The hydrocarbon feedstock can be any material with a thermoplastic nature that is liquid or becomes liquid upon heating and which has an asphaltene content from about 5 % up to about 90 % (wt).

[0035] Asphaltenes are a thermoplastic polymer, where single molecules are linked together by thermosensitive intermolecular attractive forces such as Van der Waals, dipole-dipole, and hydrogen bonding. The softening points and melting points of polymeric materials are generally related to their molecular mass, as well as the intra- and intermolecular forces within the polymer. Melting points of polymers with a molecular weight of 100 mol / g are well below -50° C, while those with a molecular weight larger than 400 mol / g are higher than 50° C. At very low temperatures, thermoplastic polymers are very brittle and exhibit high Young’s modulus, owing to the rigidity of crystalline and amorphous molecules. Astemperature rises, there is usually a sudden drop of their rigidity and Young’s modulus, because of activation of molecular movement of the amorphous chain segments. The temperature point at which Young’s modulus drops quickly is termed as the glass point, Tg, which depends on the amorphous / crystalline ratio. Between Tgand Tm(melting temperature) is the rubber-fluid state, known as the softening point, where the polymers are softened and can be pulled into filaments such as fibers.

[0036] The softening points of asphaltenes produced from solvent de-asphalting (SDA) of Alberta oilsands bitumen is known to be in the range of 160° to 170° C, while those from metallurgic pitch, is well below 150° C. The Tmof these materials are usually about 30-40° C higher than their softening points, which is typically higher than their Tg.

[0037] In contrast, the asphaltene-based precursor material used to form a carbon fiber fabric or web, as described herein, preferably has a softening point greater than about 200° C, more preferably greater than about 230° C, and most preferably greater than about 250° C. The material is then suitable for melt-extrusion or melt-spinning at a temperature between about 250° to about 300° C. If the spinning temperature is too low, the length of time to stabilize the precursor material may be lengthy, however, it is preferable not to melt-spin at a temperature where any coking takes place.

[0038] "Asphaltene-based precursor material" or "precursor material" is a material enriched in asphaltenes and may include substantially pure asphaltenes. In some embodiments, the precursor material may be produced by solvent deasphalting of a hydrocarbon feedstock. In some embodiments, the precursor material can be produced by treating a hydrocarbon feedstock as described herein or in PCT Patent Application No. PCT / CA2024 / 051360, the entire contents of which are incorporated herein by reference, where permitted.

[0039] Preferably, the asphaltene-based precursor material has been treated to raise its softening point and to be suitable for carbon fiber production. Methods to increase the softening point of a hydrocarbon material are known and are described in PCT Patent Application No. PCT / CA2021 / 000092 filed on 15 October 2021, the entire contents of which are incorporated herein by reference, where permitted.

[0040] In some embodiments, a hydrocarbon feedstock comprising asphaltenes is treated by:(a) mixing the hydrocarbon feedstock with a chemical additive to increase the softening point through cross-linking reactions;(b) heating the mixture to a first temperature (Tl) up to about 480° C in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof, stirring the mixture during heating, and holding the mixture at about Tl for a first period of time;(c) heating the mixture to a second temperature (T2) in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof and holding the mixture at about T2 for a second period of time;(d) optionally, heating the mixture to a third temperature (T3) in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof and holding the mixture at about T3 for a third period of time; and(e) separating a liquid phase enriched in asphaltenes by filtering the treated mixture.

[0041] Optionally, the liquid phase recovered from step (e) may be further treated to recover asphaltenes, such as by solvent recovery, and the asphaltenes may be used to fabricate precursor fibers. Therefore, in some embodiments, the liquid phase may be dissolved in asolvent, such as an n-alkane such as pentane or heptane, to precipitate asphaltenes as solids. These asphaltenes may then be processed into precursor fibers as described below.Chemical Additive

[0042] Initially, the hydrocarbon feedstock is mixed with a chemical additive which serves to increase the softening point through cross-linking reactions in the precursor material, preferably without significantly altering the chemistry of the original hydrocarbon material. It is preferred to control dosage of chemical additives to avoid excessive cross-linking which can convert the material to a thermosetting plastic or coke. In some embodiments, these chemical additives will decompose into intermediate products that catalyze the process of cross-linking. The intermediate products from the decomposition of additives can be further decomposed into gaseous phases that can be easily removed out of the reaction system. As a result, the chemistry of hydrocarbon materials is not altered through chemical bonding with elements of the additives.

[0043] In some embodiments, the chemical additive comprises an ammonium-, sulfur-and / or oxygen-containing-compound. The chemical additive may comprise (NH4)2SO4 (ammonium sulfate), (NH liSiOs (ammonium persulfate), (NH4)2S2O3 (ammonium thiosulfate), (NT kSCh (ammonium sulfite), NH4HSO4 (ammonium hydrogen sulfate), NH4HSO3 (ammonium hydrogen sulfite), and (NH4)2S (ammonium sulfide), or combinations thereof. At elevated temperatures, these ammonium-, sulfur- and oxygen-containing-compounds decompose into such compounds as HSO42', HSO3', S2O?2', S20s2', S2O32", SO32’ containing compounds, SO2, or S, or combinations of such compounds. These decomposition products serve as catalysts, which can cause cross-linking and / or vulcanization of hydrocarbon feedstock material to alter the hydrocarbon feedstock material to have thermoplastic properties and an increased softening or melting point. Thevulcanization or cross-linking can also lead to the hydrocarbon feedstock being converted into elastic (rubber), or thermosetting compounds.

[0044] Ammonium sulphate is one preferred chemical additive, which thermally decomposes according to reactions (1) to (3):(NH4)2SO4 = NH4HSO4 +NH3 (1)2 NH4HSO4 = (NH4)2S2O7 + H2O (2)3(NH4)2S2O7= 2NH3+ 2N2+ 6SO2+ 9H2O (3)The overall reaction is 3(NH4)2SO4 = 4NH3+ N2+3SO2+ 6H2O (4)

[0045] The intermediate products of the reaction include pyrosulfate (S2O?)2‘ and SO2.These compounds are known to cause vulcanization of a polymer compound (rubber) to an elastic and final end-use product. The above-described reactions occur within a range of temperature from about 250° C to 500° C, which coincides with the temperature range in which depolymerization, cross-linking, chain cleavage, and cracking of hydrocarbon materials can occur. The addition of (NH4)2SO4 or other ammonium-, sulfur- and / or oxygen-containing-compounds can occur at room temperature or above room temperature, for example, when the hydrocarbon feedstock is at a temperature above room temperature from a previous processing stage.

[0046] The dosage of the chemical additive can range from 0% to 20% (by weight) of the hydrocarbon feedstock to be treated, depending on the initial softening point or melting point of the hydrocarbon feedstock to be treated, the treatment temperature, the gaseous environment, the desired increase in softening point and the desired final rheological properties of the treated materials.

[0047] Further products that result from the decomposition of (NFU^SCh or other ammonium-, sulfur- and oxygen-containing-compounds, outside of those listed above are gaseous substances that preferably do not chemically react with hydrocarbon materials being treated.Heat Treatment

[0048] After, before or during mixing with the chemical additive, the feedstock is heated to a first temperature (Tl) and held and stirred for a suitable period of time with a flowing gas environment. The temperature of the hydrocarbon feedstock mixture is then adjusted to a second temperature (T2) which may lower or higher than Tl, and held for a second suitable period of time, again with stirring under a flowing gas environment. Preferably, the stirring is continuous. Optionally, the temperature of the mixture may then be adjusted to a third temperature (T3) which may be lower or higher than T2, and held for a third suitable period of time, again with continuous stirring under a flowing gas environment.

[0049] The treatment temperatures Tl, T2 and T3 must be higher than the thermal decomposition temperature of the chemical additives being added. However, treatment is preferably performed at a temperature which minimizes or avoids carbonization or coke formation, such as a temperature below 480° C.

[0050] In some embodiments, the holding time for Tl is between about 1 hour to about 4 hours, the holding time at T2 is between about 0 minutes to about 3 hours, and the holding time at T3 is between about 0 minutes to about 3 hours.

[0051] Tl, T2 and optional T3 of treatment are temperatures at which decomposition of the chemical additive takes place, and / or they can be the temperatures at which cross-linking or vulcanization reactions of hydrocarbon materials occur, and / or they can be the temperatures at which reactions between the flowing gases and the hydrocarbon materials take place. Itis also possible for all of these events to take place at the same temperature, which can be second or third temperature of the treatment.

[0052] The mixing step can occur at an ambient temperature before the step of heating, or the mixing step can occur after the hydrocarbon feedstocks are heated in the heating step. Stirring can occur after mixing and heating, or stirring can occur during any one or both of mixing and heating. As such, the method can be carried out as separately timed steps, or in different combinations of mixing, heating and stirring.

[0053] In preferred embodiments, processing temperature and time are controlled to control the rate of reaction, which affects the processability of the precursor material for meltspinning and other activated carbon processing.

[0054] The flowing gas environment in the reactor may comprise air, pure nitrogen, pure steam, an oxygen-containing gas, or combinations thereof. The gas environment serves to modify the initial hydrocarbon feedstock by attaching to chains of the hydrocarbons and making the chains longer, by cleaving side chains, or cracking heavier molecules when needed. Flowing gas also reduces the incidence of material getting deposited or stuck onto the inner sides of the treatment equipment. Depending on the desired properties of hydrocarbon materials after treatment, the selection of the type of gas streams, the temperature and the residence time can be varied during treatment. The selection of gas environments may change the effectiveness of the chemical additive in achieving crosslinking. It may also affect the alteration of chemical composition of the hydrocarbon feedstock being treated. For example, the gas may facilitate chain cleavage to remove certain side chains or molecular groups, and may facilitate dehydrogenation, leading to a decrease of the H / C ratio, which may be desired or necessary for certain applications of the treated hydrocarbon feedstock. The effectiveness of the above-described alteration ofchemical composition of the initial hydrocarbon materials is dependent of the type of processing gases.

[0055] It is preferred to continuously stir the mixture of hydrocarbon feedstock and chemical additive while heating and holding the mixture. Stirring improves heat transfer between the feedstock and the reactor wall which is being externally heated, mixing of additives with the feedstock, increases evaporation of volatile components, and encourages mixing of the gaseous medium with the hydrocarbon feedstock.

[0056] The heating of a mixture of the hydrocarbon feedstock with a chemical additive with a flowing gas stream combines various processes of molecular modification (depolymerization, cross-linking, cleavage and cracking) into a set of single process conditions in a single treatment, which conditions which can be tailored to meet various requirements of the final products.

[0057] The chemical additives thermally decompose to gaseous products, thus making minimum changes to the chemistry of original hydrocarbon feedstock and which facilitates its removal from the hydrocarbon feedstock.

[0058] After at least one heat treatment step with a chemical additive, the hydrocarbon feedstock will have less aliphatic hydrogen present. The resulting higher aromaticity is desirable when using the treated feedstock as a precursor material for making carbon fibers.

[0059] In alternative embodiments, other chemical agents could be added before and / or during each of the stepwise heat treatments for purposes other than the control of softening points and asphaltene content. For example, chemical agents could be added to produce activated carbon fibers, adding solids of any physical form to change the chemical, mechanical, electrical, thermal, and biological properties of the hydrocarbon feedstock. In some embodiments, the chemical agents may comprise a salt such as potassium carbonate,potassium bicarbonate and potassium chloride, lithium acetate, lithium citrate, lithium carbonate, lithium bicarbonate, lithium hydrogen citrate, lithium chloride, sodium oxalate, sodium hydrogen phthalate, sodium acetate, sodium citrate, sodium carbonate, sodium bicarbonate, sodium hydrogen citrate, sodium chloride, potassium oxalate, potassium potassium hydrogen phthalate, potassium acetate, potassium citrate, potassium hydrogen citrate, and derivatives thereof, and combinations thereof.

[0060] The asphaltene-based precursor material resulting from the chemical treatment at an elevated temperature is a thermoplastic material which is a liquid at an elevated temperature, but may contain various solid impurities. The solid impurities are preferably removed through using a liquid-solid separation technique, such as physical, mechanical, chemical, magnetic or electro-magnetic methods, or combinations thereof. The precursor material can be dissolved in or mixed with a solvent to liquefy or reduce the viscosity of the thermoplastic precursor material, which can facilitate liquid / solid separation.

[0061] Physical methods include sedimentation, centrifugation or decanting of solid particles that usually have higher density to the bottom of the resulting product and the top portion of the product is removed for further separation.

[0062] Mechanical methods include fdtration, which preferably involves a pressure differential to force the liquid to pass through a filter membrane, leaving the solids on the filter and a liquid filtrate. The pressure differential may be created by pressurizing the feedstock above the filter or depressurizing the chamber below the filter (vacuum separation). In some embodiments, the precursor material is filtered through a porous membrane with a pore sizes ranging from 0.1 pm to 500 pm, under pressure up to 100 psi.

[0063] Magnetic and / or electromagnetic methods may be used to remove metal species, usually metal-containing compounds, that are magnetic or can be magnetized by electric current.

[0064] Chemical methods include the addition of chemicals to react with the solid particles to form new compounds that can be easily separated by other methods. Another chemical method involves the use of a solvent to dissolve the thermoplastic portion of the solid feedstock, including asphaltenes, leaving the insoluble particles to be removed by other methods from the bulk material. The precursor material may be recovered by removing the solvent, such as through evaporation. Additionally, or alternatively, a solvent could also be added to precipitate asphaltenes as insoluble to the solvents and to remove soluble components to increase the asphaltene concentrations in the resulting products.

[0065] The asphaltene-based precursor material may be cooled during or after filtration or solids rejection. The end temperature of cooling can be room temperature or an intermediate temperature between the room temperature and the last stage of heating temperature.

[0066] In some embodiments, the asphaltene-based precursor material, after solids removal, may be further processed by solvent precipitation with n-pentane, hexane or heptane to increase the asphaltene content further. The solute comprises n-alkane soluble components and can be discarded or recovered for another purpose. The precipitated asphaltenes may then be used for melt spinning. Optionally, the precipitated asphaltenes may be subjected to one or more stages of heat treatment as described above, preferably without any additional chemical additives.

[0067] In some embodiments, precursor material recovered from different stages of heat treatment may be combined and mixed to produce a mixed precursor material for precursor fiber production. For example, spinnability and / or processability may be improved. Insome embodiments, the precursor material may require less time and lower temperature for oxidation and carbonization. In some embodiments, mechanical properties may be improved, for example, higher tensile strength, higher modulus and / or higher elongation before fracture may be achieved.Melt-Blown or Spun-Bond Processes

[0068] In one aspect, disclosed is a process of melt spinning of an asphaltene-based precursor material, which can be obtained through the staged heat-treatment with a chemical additive described above. In the process of melt-spinning, thermoplastic precursor fdaments passing through spinneret holes are further thinned to a smaller cross-section through viscous flow and rubbery flow before being cooled to the rubbery state and glassy state.

[0069] Disclosed herein are methods of producing a nonwoven precursor fabric or web by stretching and thereby thinning the precursor material leaving the spinnerets into fibers by drawing the extruded fibers with an air stream, in either a melt-blown approach or a spun-bond approach.

[0070] As used herein, a “non-woven fabric or web” means a sheet or web structure formed by entangling fibers or filaments, without weaving or knitting the fibers or filaments. A fiber can be a long continuous strand, otherwise known as a filament, or discrete fibers of shorter length.

[0071] As further used herein, a "melt-blown process" is a fiber-forming process in which a molten thermoplastic material is extruded through one or more fine orifices and attenuated into micro- or nano-scale fibers by high-velocity gas streams, the fibers being collected as a randomly oriented fibrous web on a collector surface.

[0072] A "spun-bond process" is a continuous filament-forming process in which a molten thermoplastic material is extruded through a spinneret to form substantially continuousfilaments, which are mechanically or pneumatically drawn (for example), deposited onto a collector in a controlled manner, and bonded to form a nonwoven web.

[0073] In some embodiments, a melt blown approach is used to produce fine fiber webs by extruding precursor material through a spinneret containing closely arranged small openings and attenuated by a primary stream of high-velocity air, preferably two convergent streams of heated air, as may be seen in Fig. 2. The fibers are cooled with a secondary air stream and then deposited on a collector. In some embodiments, the precursor material is fed at rate of about 0.001 to 0.05 g / min through a spinneret opening of at least 0.2 mm diameter, to produce discrete fibers having a diameter of between about 1 um to about 5 um.

[0074] In some embodiments, a spun bond process is used to produce continuous fibers by extruding the precursor material through a spinneret, which fibers are drawn by air which is moving downwards past the extruded filaments, creating a partial vacuum, and by gravitational force, may be seen in Fig. 3. The fibers are cooled through a quenching chamber below the spinneret heads. In some embodiments, the precursor material is fed at rate of about 0.05 to about 0.5 g / min through a spinneret opening of at least 0.2 mm diameter, to produce continuous fibers having a diameter of between about 5 um to about 15 um.

[0075] Regardless of the process of extrusion and thinning, flow rate of precursor material under constant precursor temperature and extruding pressure can be governed by Equations 1 and 2 shown below:M = p-D42u (1)where M is the mass of precursor flowing through the spinneret per unit time, p is the density of precursor, D is the diameter of the resulting precursor fiber, and is the spinning speed, which is proportional to the winding speed in RPM. Equation 2 is a rearrangement of Equation 1 and shows the direct correlation of filament diameter and the spinning speed.

[0076] The high strength and modulus of carbon fibers are greatly affected by the process of fiber stretching and molecular orientation achieved during fiber spinning and subsequent processing such as oxidation and carbonization. The stretching of fibrous filaments causes precursor molecules to rotate in a direction aligned with the length direction of fibrous filaments. The degree of stretching in the stage of melt-spinning will be directly related to the spinning speed. In melt-blown and spun-bond methods, faster airflow to draw the fibers results in smaller fiber diameters and higher degree of molecular alignment, and eventually high tensile strength and modulus of carbon fibers.

[0077] The speed of filament spinning is restricted by several variables, for example, the viscosity of precursor materials, the speed of fiber pulling, and homogeneity of precursor materials. Although the viscosity of precursor materials can be controlled by the temperature of precursor materials before spinning, the degree of thinning is restricted by the temperature-dependence of precursor viscosity. A strong temperature dependence of precursor viscosity results in smaller window of temperature that the filament could be thinned. For the precursors with larger window of temperature for thinning, the finer diameter can be restricted by the speed of filament pulling, for example, the speed of fiber winding, homogeneity in terms of precursor material consistency, for example, degradation of, presence of impurities, and other weakest links.

[0078] In both a melt-blown method and a spun-bond method, the precursor material fibers are deposited onto a carrier, such as a conveyor belt, and formed into a non-woven fabric or web. The fabric or web can then be processed into a carbon fiber fabric or web with twosequential processes: an initial stage of stabilization / oxidation, and a second stage where the precursor material is carbonized.

[0079] The initial stage of stabilization / oxidation may comprise a step of soaking in an aqueous solution which coats the green precursor fibers. The aqueous solution may comprise hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, their derivatives, and / or mixtures thereof. The aqueous solution can be concentrated or dilute, a dilution can be in the range of 1 wt.% to 100 wt.% of concentrated solution. The soaking time may range from 1 second to 100 minutes, preferably in the range from 5 seconds to 30 minutes. Preferably, the aqueous solution is a nitric acid solution having a concentration of between about 5% to about 40% (wt) for about 0.5 to about 30 minutes.

[0080] In some embodiments, the process of stabilization / oxidation is continued by heat treatment, preferably at a temperature between about 200° to 400° C in a gas including oxygen to cross-link the molecules. The time required to achieve stabilization is sensitive to the nature of precursors. In general, the rate of reaction in stabilization becomes meaningful at temperatures above 200° C. At a stabilization lower than 200° C, the reaction is very sluggish and is not economical as a result. On the other hand, higher oxidation temperatures require much shorter time but can lead to overoxidation and poor mechanical properties of the resulting carbon fibers. Generally, a higher softening point requires shorter stabilization times. It is preferred that the softening points of precursor material to be in the range of 230° C to 280° C for asphaltene-based precursors.

[0081] Once stabilized and / or oxidized, carbonization can take place at much higher temperatures, typically about 1000° to 2000° C, in an environment without oxygen.Optionally, the carbonized fiber fabric or web can then be graphitized, typically at temperatures up to 3000° C.

[0082] By way of further description of the process of the present disclosure, reference may be made to the following examples, which are intended to exemplify certain elements of the claimed invention, not limit them. Unless otherwise indicated, all parts and percentages are by weight.

[0083] Example 1 - Production of Spun Bond Fiber Webs

[0084] An asphaltenes-based precursor was produced to achieve a melt-spinnable temperature of 290° C. 50 kg of vacuum refinery residues (VRR) as hydrocarbon feedstock was mixed with (NH4)2SO4 solid powder at 6 wt. % of vacuum refinery residues. The VRR feedstock was a viscous liquid at room temperature and its softening point was below room temperature, but not measured. The mixture was placed in a sealed cylindrical reactor and stirred at a rate of 30 RPM (revolutions per minute) as the mixture was treated with the following sequential steps:a) 1st step of heating to 350°C and held at 350° C for 120 minutes with a flow of N2 gas;b) 2nd step of heating to 420°C and held at 420°C for 60 minutes with a flow of N2 gas;c) 3rd step of heating to 435°C and held at 435°C for 75 minutes with a flow of steam, andd) filtering of the resulting hydrocarbons before cooling the liquid filtrate to room temperature with a flow of nitrogen gas.

[0085] The liquid filtrate comprised an asphaltene-based precursor material, with a yield of 51%, and which solidified upon cooling to room temperature. This precursor material had a melt-spinning temperature of 180° C.

[0086] The precursor material was then dissolved in pentane with a ratio of 20 liters of pentane to 1 kg. Insoluble solids were placed in a sealed cylindrical reactor and were then heated to 300° C for 120 minutes, with stirring at 30 RPM and a flow of N2 gas. The resulting precursor material had a spinning temperature of 290° C.

[0087] The precursor material was ground into powders with an average diameter of about 5 mm and loaded to a barrel to feed a single screw extruder that was heated along the length of the extruder to an end temperature for melt-spinning. The volume of precursor feeding was controlled by a metering pump above the spinneret head that had 1000 spinneret holes lined and spaced equally over 0.5 meter wide. The distance between the spinneret head and the conveying belt where the produced precursor fibers were laid was controlled to be about 1.0 m. In this example, three different values of metering pump were used to produce precursors fibers, they were 100, 170, and 250 ml / min. In each of these tests, the air flow rate to pull the melt precursor out of the surface of spinneret holes into thinned fibers was controlled by the rotation speed of air fan with a maximum rotation speed of 3000 RPM and air volume capacity of 11 m3 / min. In the current example, the rotation speed of air fan was set to 2000 RPM for all the tests.

[0088] The spun-bond system is conceptually similar to that shown in Fig. 3.

[0089] The precursor fiber fabric produced at different metering pump volumes were cut into small samples for various processing and characterization. First, the precursor fiber fabric was presoaked in 30% nitric acid for about 1 minute before being transferred to an oven for stabilization.

[0090] Following nitric acid soak, the precursor fiber fabric produced by this spunbond approach were stabilized at 260° C for 90 minutes in flowing air. The stabilization was followed by the process of carbonization that was performed at 1200° C for 2 hours in flowing nitrogen atmosphere. The resulting carbon fibers were tensile tested to determine tensile strength and modulus, according to ASTM C1557-20 Standard Test Method for Tensile Strength and Young's Modulus of Fibers. To ensure proper alignment of the carbon fibers with the loading axis, each fiber was bonded to two parallel paper tabs at its ends and the paper tabs were gripped and pulled to load the fiber. The gauge length of fiber was fixed at 1.27 cm. The carbon fiber diameters were measured on a high-resolution optical microscope to calculate the tensile properties. The processing parameters and the mechanical properties of resulting carbon fibers are listed in Table 1. As seen in Table 1, higher volume of precursor feeding results in higher precursor fiber diameter and lower tensile properties.Table 1. Conditions of melt spun bond of an asphaltene-based precursor and the characteristics of resulted fibers - effect of precursor feeding rate.

[0091] Example 2 - Spinning Heads with Different Diameters of Spinneret Hole

[0092] The same precursor and methodology as detailed in Example 1 were used to produce precursor fiber fabrics by spun bond approach. However, spinning heads with different diameters of spinneret hole were used in the current example, as listed in Table 2. Spinning heads with larger spinneret hole diameters produced fibers with slightly smaller diameters but much higher tensile properties.Table 2. Conditions of melt spunbond of an asphaltene-based precursor and the characteristics of resulted fibers - effect of spinneret hole size

[0093] Example 3 - Varying Air Flow Rates

[0094] The same precursor and methodology as detailed in Example 1 were used to produce precursor fiber fabrics by a spun-bond approach. However, different air flow rates to pull precursor fibers below spinneret head were used in the current example, as listed in Table 3. Higher air flow rate produced fibers with smaller fiber diameters but much higher tensile strength and modulus.Table 3. Conditions of melt spunbond of an asphaltene-based precursor and the characteristics of resulted fibers - effect of air suction force

[0095] Example 4 - Production of Melt Blown Fiber Webs

[0096] The same precursor material as detailed in Example 1 was used to produce precursor fiber fabrics by melt blown approach, using a system conceptually similar to that shown in Fig. 2. Different levels of precursor feeding in terms of precursor volume per minute were used. The resulting diameters of precursor fibers were measured as listed in Table 4.

[0097] The precursor fiber fabric produced under the conditions listed in Table 4 were cut into small samples for various processing and characterization. First, the precursor fibers were presoaked in 30% nitric acid for about 1 minute before being transferred to an oven for stabilization.

[0098] The resulting precursor fibers were stabilized by oxidation at 260°C for about 60 minutes in air, and then carbonized at 1200°C for 120 minutes in flowing nitrogen gas. The resulting fibers were tensile tested to determine tensile strength and modulus, according to ASTM C1557-20 Standard Test Method for Tensile Strength and Young's Modulus of Fibers. To ensure proper alignment of the carbon fibers with the loading axis, each fiber was bonded to two parallel paper tabs at its ends and the paper tabs were gripped and pulled to load the fiber. The gauge length of fiber was fixed at 1.27 cm. The carbon fiber diameters were measured on a high-resolution optical microscope to calculate the tensile properties. The processing parameters and the mechanical properties of resulting carbon fibers are listedin Table 4. Higher rate of precursor volume inputs results in higher precursor fiber diameter and lower tensile properties.Table 4. Conditions of melt blown of an asphaltene-based precursor and the characteristics of resulted fibers - effect of precursor feeding rate.

[0099] Example 5 - Spinning Heads with Different Diameters of Spinneret Hole

[0100] The same precursor and methodology as detailed in Example 4 were used to produce precursor fiber fabrics by melt blown approach. However, spinning heads with different diameters of spinneret hole were used in the current example, as listed in Table 5. Spinning heads with larger spinneret hole diameters produced fibers having slightly smaller diameters but much higher tensile properties.Table 5. Conditions of melt blown and the characteristics of resulting fibers-Effect of spinneret hole size.

[0101] Example 6 - Varying Air Flow Rates

[0102] The same precursor and methodology as detailed in Example 4 were used to produce precursor fiber fabrics by melt blown approach. However, different air flow rates to stretch precursor fibers were used in the current example, as listed in Table 6. Higher air flow rate produced fibers with smaller fiber diameters but much higher tensile strength and modulus.Table 6. Conditions of melt blown of an asphaltene-based precursor and the characteristics of resulted fibers - effect of air suction forceInterpretation.

[0103] The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims appended to this specification are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed.

[0104] References in the specification to "one embodiment", "an embodiment", etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to thesame embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such module, aspect, feature, structure, or characteristic with other embodiments, whether or not explicitly described. In other words, any module, element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility, or it is specifically excluded.

[0105] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as "solely," "only," and the like, in connection with the recitation of claim elements or use of a "negative" limitation. The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

[0106] The singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. The term "and / or" means any one of the items, any combination of the items, or all of the items with which this term is associated. The phrase "one or more" is readily understood by one of skill in the art, particularly when read in context of its usage.

[0107] The term "about" orcan refer to a variation of ± 5%, ± 10%, ± 20%, or ± 25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" orcan include one or two integers greater than and / or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term "about"is intended to includevalues and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0108] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.

[0109] As will also be understood by one skilled in the art, all language such as "up to", "at least", "greater than", "less than", "more than", "or more", and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.

Claims

CLAIMS1. A method of making carbon fiber fabrics or webs by a spun bond approach, comprising:a. forming fibers by melt-extruding an asphaltene-based precursor material through a spinneret opening at a spinning temperature greater than about 200° C;b. drawing the fibers by airflow to reduce the diameter of the fibers; c. depositing the drawn fibers to form a fabric or a web;d. stabilizing and / or oxidizing the fabric or web, preferably by soaking the fabric or web in a nitric acid bath and stabilizing the fabric or web in air; and e. carbonizing the fabric or web.

2. The method of claim 1, wherein said step (a) of forming takes place at a temperature of about 200°C to 320°C, preferably at a temperature between about 280° C and 300° C.

3. The method of claim 1 or claim 2, where said step (b) of drawing reduces said fibers’ diameter to about 1 / 10 to about 1 / 150 of the diameter of the spinneret opening.

4. The method of claim 3, wherein said spinneret opening has a diameter of about 0.2 mm or greater.

5. The method of any one of claims 1-4, where the nitric acid bath has a nitric acid concentration ranging from 5 to 40%.

6. The method of claim 5, where the nitric acid soak is for a period ranging from 0.5 to 30 minutes.

7. The method of any one of claims 1-6, wherein the fabric or web is stabilized in air at a temperature between about 200° C to 350° C, for a period of between 1 minute to about 2 hours.

8. The method of any one of claims 1-7, wherein the precursor flow rate through each spinneret opening is 0.001 to 0.05 g / min and the fibers are discrete fibers.

9. The method of any one of claims 1-7 wherein the precursor flow rate is 0.05 to 0.5 g / min and the fibers are continuous fibers.

10. A carbon fiber fabric or web formed by the process of claim 8, comprising a carbon fiber having a minimum tensile strength of 3000 MPa.

11. A carbon fiber fabric or web formed by the process of claim 9, comprising a carbon fiber having a minimum tensile strength of 2000 MPa.

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