Melt Spinning Lignin/Acrylic Fibers

This application claims benefit of and priority to U.S. Provisional Patent Application Ser. No. 63/342,537, filed May 16, 2022, the disclosure of which is incorporated herein by reference in its entirety.

The presently disclosed subject matter relates in some embodiments to methods of preparing fibers comprising a polyacrylonitrile (PAN). In some embodiments, the method comprises melt-spinning a mixture of solids comprising a PAN and a meltable solvent. In some embodiments, the meltable solvent can be removed after fiber formation. In some embodiments, the mixture of solids can further comprise lignin. In some embodiments, the fibers can be used in acrylic fiber applications, e.g., in clothing, furnishing, and as construction/building materials. In some embodiments, the fibers can be used as carbon fiber precursors. Thus, in some embodiments, the presently disclosed subject matter further relates to carbon fiber precursors fibers, carbon fibers and to related composites.

Melt-spinning is a commercially important fiber formation method. In 2016, melt-spun polyester, polyamides, and polypropylene accounted for 86% of global synthetic fiber production.The high textile-grade yarn production speeds of 4000 m/min and cost-effective, typically solvent-less nature of melt-spinning makes melt spinning preferable compared to solution spinning methods.However, melt-spinning is generally restricted to thermoplastic polymers that have a higher degradation temperature than melting temperature (T). In addition, the unprocessability of high viscosity melts, such as high molecular weight thermoplastics (e.g., ultra-high molecular weight polyethylene), limits melt spinning to lower molecular weight polymer systems than those that can be diluted in solution spinning.

Acrylic fibers are among those typically solution spun due to chemical degradation that can occur at temperatures lower than the melting point temperature of the polyacrylonitrile (PAN) polymers from which these fibers are prepared.The presence of the dipole-dipole interactions between nitrile groups in PAN both increases the Tof the polymer, and also induces exothermic reactions such as cyclization, dehydrogenation, aromatization, oxidation, and crosslinking at temperatures within 200-300° C. in air.As a result, PAN fibers are solution spun through dry, wet, and gel spinning practices. Wet and gel spinning are used, for example, for producing precursor-grade PAN fibers for carbon fiber conversion. While effective in producing precursors for high modulus and high strength carbon fiber, solution spinning PAN for carbon fiber conversion has a high production cost. In addition, there is a scarcity of commercial solution spinning operations in the United States that can accommodate flammable solvents.

Accordingly, there is an ongoing need to find new methods of preparing fibers from acrylic polymers. In particular, there is an ongoing need for new and effective methods of melt-spinning PAN fibers. There is also an ongoing need for methods of melt-spinning PAN fibers that incorporates renewable materials, such as lignin.

This summary lists several embodiments of the presently disclosed subject matter, and in many cases lists variations and permutations of these embodiments. This summary is merely exemplary of the numerous and varied embodiments. Mention of one or more representative features of a given embodiment is likewise exemplary. Such an embodiment can typically exist with or without the feature(s) mentioned; likewise, those features can be applied to other embodiments of the presently disclosed subject matter, whether listed in this summary or not. To avoid excessive repetition, this Summary does not list or suggest all possible combinations of such features.

In some embodiments, the presently disclosed subject matter provides a method of preparing a fiber, wherein the method comprises: (a) preparing a mixture of solids comprising polyacrylonitrile (PAN), lignin, and a meltable solvent; and (b) melt-spinning said mixture of solids; thereby preparing the fiber. In some embodiments, the mixture of solids comprises up to about 30 weight (wt) % lignin, optionally about 10 wt % lignin and/or wherein the lignin comprises or consists of kraft softwood lignin. In some embodiments, the meltable solvent comprises or consists of dimethyl sulfone (DMSO-2), optionally wherein the mixture of solids comprises about 40 wt % to about 60 wt % DMSO-2.

In some embodiments, the PAN comprises a copolymer of acrylonitrile (AN) and up to about 15 mole (mol) % of one or more comonomers, optionally wherein the one or more comonomers are selected from the group comprising methyl acrylate (MA), vinyl acetate, ethyl vinyl ether, vinyl bromide, vinylidene chloride, and vinyl chloride. In some embodiments, the copolymer is a copolymer of AN and MA, optionally wherein the copolymer comprises about 8 mole (mol) % MA. In some embodiments, the PAN has a viscosity average molecular weight (M) of about 50 kilograms per mole (kg/mol) to about 250 kg/mol, optionally about 80 kg/mol. In some embodiments, the PAN is a polymer or copolymer of biomass-derived AN and/or wherein the PAN is derived from pre- or post-consumer waste.

In some embodiments, the mixture of solids further comprises one or more additives, optionally comprising at least one antiplasticizer.

In some embodiments, the melt-spinning of step (b) is performed at a temperature of about 150° C. to about 220° C. and/or wherein the melt-spinning is performed using a take-up speed of about 40 meters per minute (m/min) to about 100 m/min. In some embodiments, the melt-spinning of step (b) is performed by melt-spinning a melt prepared from pellets, wherein said pellets are provided by melt-compounding the mixture of solids to provide a melt of the mixture of solids, optionally at a temperature of 90° C. to about 180° C.; extruding the melt to provide a rod; and chopping the rod to provide the pellets. In some embodiments, the method further comprises washing the fiber to remove the meltable solvent, optionally wherein the washing comprises submerging the fiber in water at a temperature up to about 100° C., further optionally wherein the water has a temperature of about 95° C. and/or wherein the fiber is submerged in the water for a period of time between about 10 seconds to about 300 seconds.

In some embodiments, the fiber is a carbon fiber precursor and the method further comprises carbonizing the fiber to provide a carbonized fiber, optionally wherein the method further comprises graphitizing the carbonized fiber to provide a carbon fiber.

In some embodiments, the presently disclosed subject matter provides a fiber prepared according to a method comprising (a) preparing a mixture of solids comprising polyacrylonitrile (PAN), lignin, and a meltable solvent; and (b) melt-spinning said mixture of solids, thereby preparing the fiber, optionally wherein said fiber is a carbon fiber or wherein said fiber is a carbon fiber precursor comprising about 30 wt % to about 50 wt % lignin and/or having a diameter of about 15 micrometers or less. In some embodiments, the presently disclosed subject matter provides a carbon fiber composite comprising the carbon fiber prepared as described herein.

In some embodiments, the presently disclosed subject matter provides a method of preparing a fiber, wherein the method comprises: (a) preparing a mixture of solids comprising PAN and a meltable solvent, wherein said mixture is substantially free of water or a PAN hydrate; and (b) melt-spinning said mixture of solids; thereby preparing the fiber. In some embodiments, the meltable solvent comprises or consists of DMSO-2, optionally wherein the mixture of solids comprises about 40 wt % to about 60 wt % DMSO-2.

In some embodiments, the PAN comprises a copolymer of AN) and up to about 15 wt % of one or more comonomers, optionally wherein the one or more comonomers are selected from the group comprising MA, vinyl acetate, ethyl vinyl ether, vinyl bromide, vinylidene chloride, and vinyl chloride, further optionally wherein the copolymer is a copolymer of AN and MA.

In some embodiments, the method further comprises washing the fiber to remove the meltable solvent, optionally wherein the washing comprises submerging the fiber in water at a temperature up to about 100° C., further optionally wherein the water has a temperature of about 95° C. and/or wherein the fiber is submerged in the water for a period of time between about 10 seconds to about 300 seconds. In some embodiments, the fiber is a carbon fiber precursor and the method further comprises carbonizing the fiber to provide a carbonized fiber, optionally wherein the method further comprises graphitizing the carbonized fiber to provide a carbon fiber.

In some embodiments, the presently disclosed subject matter provides a fiber prepared according to a method comprising (a) preparing a mixture of solids comprising PAN and a meltable solvent, wherein said mixture is substantially free of water or a PAN hydrate; and (b) melt-spinning said mixture of solids; thereby preparing the fiber.

It is an object of the presently disclosed subject matter to provide methods of preparing fibers from mixtures comprising polyacrylonitrile, as well as to related carbon fiber precursors, carbon fibers, and carbon fiber composites. This and other objects are achieved in whole or in part by the presently disclosed subject matter. Further, an object of the presently disclosed subject matter having been stated above, other objects and advantages of the presently disclosed subject matter will become apparent to those skilled in the art after a study of the following description and Figures.

According to one aspect of the presently disclosed subject matter, described are additives that can plasticize or dissolve PAN polymers at elevated temperatures, and which can reduce the melting temperature of these polymers for melt-spinning acrylic fiber. Accordingly, in some embodiments, the presently disclosed subject matter relates to a method of preparing melt-spun acrylic fibers (i.e., fibers prepared from PAN homopolymers and/or PAN copolymers (copolymers comprising at least 85% acrylonitrile (AN)-derived monomeric units)). In some embodiments, the melt-spinning comprises compounding a PAN polymer with a meltable solvent (e.g., dimethyl sulfone (DMSO-2)). The melt-spun fibers can be used in various acrylic fiber applications, e.g., clothing, upholstery, carpets, building/construction materials. In some embodiments, the melt-spun acrylic fibers are useful as carbon fiber precursors (i.e., carbon fiber precursor fibers, which are fibers that can be carbonized and graphitized to provide carbon fibers).

In some embodiments, the acrylic polymer or polymers are compounded with lignin. Thus, in some embodiments, the presently disclosed subject matter relates to methods of preparing lignin/PAN fibers, as well as to the carbon fiber precursor fibers and carbon fibers prepared therefrom, and to carbon fiber composites prepared from the carbon fibers. Of the 50 million tons of lignin released by the pulp and paper industry in a year, lignin remains an under-utilized source of fuel or additive. Thus, the successful deployment of lignin into applications for carbon fiber as described herein can expand markets for those fibers into value-added consumer and industrial goods. In some embodiments, the presently disclosed fibers (e.g., the presently disclosed carbon fiber precursor fibers) can comprise about 30 weight (wt) % lignin or more (e.g., about 30 wt % to about 50 wt % lignin). In some embodiments, the presently disclosed subject matter relates to a method comprising melt-spinning lignin-acrylic polymers compounded with a meltable solvent.

Due to the scarcity of commercial solution spinning operations in the United States that can handle flammable solvents, the melt spinning of acrylic polymers or acrylic polymer/lignin blends, compounded with a meltable solvent, represents a significant step toward the production of sustainable, low cost synthetic fiber and carbon fiber precursors. In addition, the presently disclosed subject matter can be used to recycle acrylic polymers (e.g., pre- or post-consumer acrylic resin or acrylic fiber waste, such as but not limited to pre- or post-consumer PAN homopolymer waste), wherein the recycling can include melt-compounding waste acrylic polymers (e.g., waste PAN homopolymer) with a meltable solvent (e.g., DMSO-2 powder) and melt-spinning fibers therefrom. In some embodiments, the recycling (e.g., of shredded acrylic waste fibers) can be performed using commercially available plastic recycling systems, such as, but not limited to, a recycling system sold under the tradename EREMA® (EREMA Engineering Recycling Maschinen und Anglagen Ges.b.b.H., Ansfelden, Austria).

The presently disclosed subject matter will now be described more fully. The presently disclosed subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein below and in the accompanying Examples. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art.

All technical and scientific terms used herein, unless otherwise defined below, are intended to have the same meaning as commonly understood by one of ordinary skill in the art. References to techniques employed herein are intended to refer to the techniques as commonly understood in the art, including variations on those techniques or substitutions of equivalent techniques that would be apparent to one of skill in the art.

In describing the presently disclosed subject matter, it will be understood that a number of techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques.

Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the presently disclosed and claimed subject matter.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the presently disclosed subject matter.

While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in this application, including in the claims. Thus, as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. For example, the phrase “fiber” refers to one or more fibers, including a plurality of the same type of fiber. Similarly, the phrase “at least one”, when employed herein to refer to an entity, refers to, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, or more of that entity, including but not limited to whole number values between 1 and 100 and greater than 100. As such, the terms “a”, “an”, “one or more” and “at least one” can be used interchangeably. Similarly, the terms “comprising”, “including” and “having” can be used interchangeably. 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 use of such exclusive terminology as “solely,” “only” and the like, in connection with the recitation of claim elements, or use of a “negative” limitation.

Unless otherwise indicated, all numbers expressing quantities of temperature, time, concentration, length, width, height, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. The term “about”, as used herein when referring to a measurable value such as an amount of mass, weight, time, volume, length, width, or temperature is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods and/or employ the disclosed subject matter. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, some embodiments includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms an embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that when a value is disclosed that “less than or equal to” the value, “greater than or equal to the value” and possible ranges between values are also disclosed, as appropriately understood by the skilled artisan. For example, if the value “10” is disclosed, then “less than or equal to 10” as well as “greater than or equal to 10” are also disclosed. It is also understood that the throughout the application, data are provided in a number of different formats, and that these data represent in some embodiments endpoints and starting points and in some embodiments ranges for any combination of the data points. For example, if a particular data point “10” and a particular data point “15” are disclosed, it is understood that greater than, greater than or equal to, less than, less than or equal to, and equal to 10 and 15 are considered disclosed as well as between 10 and 15. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

Numerical ranges recited herein by endpoints include all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, 4.24, and 5). Similarly, numerical ranges recited herein by endpoints include subranges subsumed within that range (e.g. 1 to 5 includes 1-1.5, 1.5-2, 2-2.75, 2.75-3, 3-3.90, 3.90-4, 4-4.24, 4.24-5, 2-5, 3-5, 1-4, and 2-4).

As used herein, the term “and/or” when used in the context of a list of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and/or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C, and D.

The term “comprising”, which is synonymous with “including” “containing”, or “characterized by”, is inclusive or open-ended and does not exclude additional, unrecited elements and/or method steps. “Comprising” is a term of art that means that the named elements and/or steps are present, but that other elements and/or steps can be added and still fall within the scope of the relevant subject matter.

As used herein, the phrase “consisting essentially of” limits the scope of the related disclosure or claim to the specified materials and/or steps, plus those that do not materially affect the basic and novel characteristic(s) of the disclosed and/or claimed subject matter.

As used herein, the phrase “consisting of” excludes any element, step, or ingredient not specifically recited. It is noted that, when the phrase “consists of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

With respect to the terms “comprising”, “consisting of”, and “consisting essentially of”, where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms.

The terms “optional” and “optionally” as used herein indicate that the subsequently described event, circumstance, element, and/or method step may or may not occur and/or be present, and that the description includes instances where said event, circumstance, element, or method step occurs and/or is present as well as instances where it does not.

The term “vinyl” refers to a chemical functional group having the formula-CH═CH.

The term “acrylate” as used herein can refer to salts, conjugate bases and esters of acrylic acid, as well as to related polymers. Thus, in some embodiments, the term “acrylate” can refer to a compound having the formula CH═CH—C(═O)—O—R, where R is H, alkyl, substituted alkyl, aralkyl, substituted aralkyl, aryl, or substituted aryl, as well as to polymers (which can also be referred to as “polyacrylates”) prepared by polymerizing such compounds. In some embodiments, acrylate polymers can include polymers prepared from monomers that are derivatives of acrylates or mixtures of monomers that include acrylate derivatives. Acrylate derivatives include, for example, methyl methacrylate and acrylonitrile, i.e., a compound where the carboxylate group of acrylic acid is replaced by a nitrile group, i.e., a chemical functional group where a carbon atom is bound to a nitrogen atom via a triple bond.

The term “acrylonitrile” or “AN” refers to the compound having the formula CH═CH—CN (i.e., CH═CH—C≡N).

The term “polyacrylonitrile” or “PAN”, as used herein, refers to a homo- or copolymer comprising repeating constitutional “monomeric” units derived from AN or AN and one or more additional vinyl monomers. According to the presently disclosed subject matter, at least 85% of the monomeric units in a PAN copolymer are monomeric units derived from AN. The PAN polymers can also be referred to herein as “acrylic polymers”, while fibers prepared from PAN can also be referred to herein as “acrylic fibers.” In contrast, fibers prepared from copolymers prepared by polymerizing a mixture of monomers comprising at least 35% but less than 85% AN can be referred to as “modacrylics.”

As used herein, a “monomer” refers to a non-polymeric molecule that can undergo polymerization, thereby contributing repeating constitutional units (or “monomeric units”), i.e., an atom or group of atoms, to the essential structure of a macromolecule.

As used herein, a “macromolecule” refers to a molecule of high relative molecular mass, the structure of which comprises the multiple repetition of units derived from molecules of low relative molecular mass, e.g., monomers and/or oligomers.

An “oligomer” refers to a molecule of intermediate relative molecular mass, the structure of which comprises a small plurality (e.g., 2, 3, 4, 5, 6, 7, 8, 9, or 10) of repetitive units derived from molecules of lower relative molecular mass.

As used herein the terms “polymer”, “polymeric” and “polymeric matrix” refer to a substance comprising macromolecules. In some embodiments, the term “polymer” can include both oligomeric molecules and molecules with larger numbers (e.g., >10, >20, >50, >100) of repetitive units. In some embodiments, “polymer” refers to macromolecules with at least 10 repetitive units. A “copolymer” refers to a polymer derived from more than one species of monomer (e.g., prepared by polymerizing a mixture of more than one particular monomer). Copolymers can have a random arrangement of monomeric units (i.e. be a “random copolymer) or can have “blocks” of oligo- or polymeric chains derived from one type of monomer attached to blocks derived from another type of monomer.

The term “thermoplastic” can refer to a polymer that softens and/or can be molded above a certain temperature, but which is solid below that temperature.

The term “bioplastic” refers to thermoplastic polymers that can be prepared from renewable sources (e.g., monomers derived from plant matter), which can also be referred to as “biobased”.

“Biodegradable” means materials that are broken down or decomposed by natural biological processes. Biodegradable materials can be broken down for example, by cellular machinery, proteins, enzymes, hydrolyzing chemicals or reducing agents present in biological fluids or soil, intracellular constituents, and the like, into components that can be either reused or disposed of without significant toxic effect on the environment. Thus, the term “biodegradable” as used herein refers to both enzymatic and non-enzymatic breakdown or degradation of polymeric structures. In some embodiments, the degradation time is a function of polymer composition and morphology. Suitable degradation times are from hours or days to weeks to years.

The term “saccharide” refers to a carbohydrate monomer, oligomer or larger polymer. Thus, a saccharide can be a compound that includes one or more cyclized monomer unit based upon an open chain form of a compound having the chemical structure H(CHOH)C(═O)(CHOH)H, wherein the sum of n+m is an integer between 2 and 8 (e.g., 2, 3, 4, 5, 6, 7, or 8). Thus, the monomer units can include trioses, tetroses, pentoses, hexoses, heptoses, nonoses, and mixtures thereof. In some embodiments, each cyclized monomer unit is based on a compound having a chemical structure wherein n+m is 4 or 5.

Thus, saccharides can include monosaccharides including, but not limited to, aldohexoses, aldopentoses, ketohexoses, and ketopentoses such as arabinose, lyxose, ribose, xylose, ribulose, xylulose, allose, altrose, galactose, glucose, gulose, idose, mannose, talose, fructose, psicose, sorbose, and tagatose, and to hetero- and homopolymers thereof. Saccharides can also include disaccharides including, but not limited to sucrose, maltose, lactose, trehalose, and cellobiose, as well as hetero- and homopolymers thereof.

The term “lignocellulosic” refers to a composition comprising both lignin and cellulose. In some embodiments, lignocellulosic material can comprise hemicellulose, a polysaccharide which can comprise saccharide monomers other than glucose. Typically, lignocellulosic materials comprise about 30-45 weight % cellulose, about 20-35 weight % hemicellulose; and about 3-35 weight % lignin.