CROSS REFERENCE TO RELATED APPLICATIONS

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

TECHNICAL FIELD

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.

BACKGROUND

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. ¹ 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. ² However, melt-spinning is generally restricted to thermoplastic polymers that have a higher degradation temperature than melting temperature (Tm). 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. ³ ' ⁶ The presence of the dipole-dipole interactions between nitrile groups in PAN both increases the T _m of the polymer, and also induces exothermic reactions such as cyclization, dehydrogenation, aromatization, oxidation, and crosslinking at temperatures within 200-300°C in air. ⁷ 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.

SUMMARY

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 _v ) 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 postconsumer 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 takeup 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.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1A is a composite graph showing the thermogravimetric analysis (TGA) of polyacrylonitrile (PAN) powder, Kraft lignin, dimethyl sulfone (DMSO-2, which can also be referred to as methyl sulfonylmethane (MSM)), and 60 weight (wt) % PAN/DMSO-2 pellets. The graph plots weight (as a percentage (%) of the initial weight) versus temperature (in degrees Celsius (°C). Vertical dashed lines are shown at 180°C and 270°C.

Figure IB is a composite graph showing the differential thermogravimetric analysis (DTGA) of polyacrylonitrile (PAN) powder, Kraft lignin, dimethyl sulfone (DMSO-2), and 60 weight (wt) % PAN/DMSO-2 pellets. The graph plots weight percentage change per degree Celsius (%/°C) versus temperature (°C). Vertical dashed lines are shown at 180°C and 270°C.

Figure 2 is a pair of photographic images showing (left) melt spun polyacrylonitrile (PAN)/dimethyl sulfone (DMSO-2) as spun (AS) filaments and (right) PAN-Kraft lignin (KL)/DMSO-2 AS filaments.

Figure 3 is a graph showing the Fourier transform infrared (FTIR) spectra (absorbance versus wavenumber (in inverse centimeters (cm ⁴ ))) of different washing intervals (0 to 300 seconds (sec)) of neat polyacrylonitrile (PAN)/dimethyl sulfone (DMSO- 2) as spun filaments. The FTIR spectra of DMSO-2 and PAN powder are also shown for comparison. Vertical dashed lines are shown at 2242, 1283, 1130, 933, and 760 cm' ¹ .

Figure 4A is a series of scanning electron microscopy (SEM) micrographs of crosssections of neat (top) and washed (bottom) as spun (AS) melt spun polyacrylonitrile (PAN) filaments prepared at take up speeds of 40 meters per minute (m/min) (left), 80 m/min (middle), and 100 m/min (right). The scale bars in the lower right comer of each micrographs represent 200 micrometers.

Figure 4B is a photographic image showing spools of exemplary fibers described in Figure 4 A.

Figure 5A is a graph showing the effect of washing and take-up speed (40 meters per minute (m/min), 80 m/min, or 100 m/min) on linear density (den) of polyacrylonitrile (PAN) filaments. Neat refers to as spun (non-washed) PAN filament.

Figure 5B is a graph showing the effect of washing and take-up speed (40 meters per minute (m/min), 80 m/min, or 100 m/min) on cross-sectional area (square micrometer (pm ² )) of polyacrylonitrile (PAN) filaments. Neat refers to as spun (non-washed) PAN filament.

Figure 6A is a graph showing the X-Ray diffraction (XRD) spectra of neat melt spun polyacrylonitrile (PAN) filaments prepared at different take-up speeds (i.e., 40 meters per minute (40 Neat), 80 meters per minute (80 Neat), or 100 meters per minute (100 Neat) compared to the spectra of dimethyl sulfone (DMSO2). The spectra show intensity (in counts) versus 2 theta (20, in degrees (deg)). Vertical dashed lines are shown at 17 and 30 deg.

Figure 6B is a graph showing the X-Ray diffraction (XRD) spectra of washed melt spun polyacrylonitrile (PAN) filaments prepared at different take-up speeds (i.e., 40 meters per minute (40 Neat), 80 meters per minute (80 Neat), or 100 meters per minute (100 Neat) compared to the spectra of dimethyl sulfone (DMSO2). The spectra show intensity (in counts) versus 2 theta (20, in degrees (deg)). Vertical dashed lines are shown at 17 and 30 deg.

Figure 7A is a graph showing the effect of washing on tenacity (grams per denier (g/den)) of polyacrylonitrile (PAN) filaments prepared at different take-up speeds (i.e., 40 meters per minute (m/min) (40), 80 m/min (80), or 100 m/min (100)). Neat refers to as spun (non-washed) PAN filaments.

Figure 7B is a graph showing the effect of washing on modulus (grams per denier (g/den)) of polyacrylonitrile (PAN) filaments prepared at different take-up speeds (i.e., 40 meters per minute (m/min) (40), 80 m/min (80), or 100 m/min (100). Neat refers to as spun (non-washed) PAN filaments.

Figure 7C is a graph showing the effect of washing on percent (%) strain at break of polyacrylonitrile (PAN) filaments prepared at different take-up speeds (i.e., 40 meters per minute (m/min) (40), 80 m/min (80), or 100 m/min (100)). Neat refers to as spun (nonwashed) PAN filaments.

Figure 7D is a graph showing the effect of washing on toughness (grams per denier (g/den)) of polyacrylonitrile (PAN) filaments prepared at different take-up speeds (i.e., 40 meters per minute (m/min) (40) 80 m/min (80), or 100 m/min (100)). Neat refers to as spun (non-washed) PAN filaments.

Figure 8A is a graph showing load versus extension (stress (grams per denier (g/den)) versus strain (percentage (%))) of neat (solid lines) and washed (dashed lines) polyacrylonitrile (PAN) filaments prepared at different take-up speeds: 40 meters per minute (m/min) (40 Neat and 40 Washed), 80 m/min (80 Neat and 80 Washed), or 100 m/min (100 Neat and 100 Washed).

Figure 8B is a series of micrographs showing neat (bottom row) and washed (top row) polyacrylonitrile (PAN) filaments described for Figure 8A. Filaments prepared at 40 meters per minute take-up speed are shown in the left-hand column; filaments prepared at 80 meters per minute take-up speed are shown in the middle column; and filaments prepared at 100 meters per minute take-up speed are shown in the right-hand column. The scale bar in the bottom right comer of each micrograph represents 100 micrometers (pm).

Figure 9A is a schematic cut away side view of a twin-screw extruder suitable for use in a method of the presently disclosed subject matter, e.g., for use in melt compounding mixtures of solids comprising PAN and a meltable solvent according to an embodiment of the presently disclosed subject matter.

Figure 9B is a schematic view of an apparatus for melt-spinning fibers, including bicomponent fibers, according to an embodiment of the presently disclosed subject matter.

Figure 9C is a schematic cut away side view of an exemplary spinning pack configuration for use in an apparatus of Figure 9B. The spinning pack can be used, if desired, for the preparation of core-sheath bicomponent fibers comprising a core prepared from a first mixture of solids and a sheath prepared from a second mixture of solids.

Figure 9D is a schematic perspective view showing an alternative apparatus for use in preparing fibers according to an embodiment of the presently disclosed subject matter.

Figure 9E is a schematic cut away side view of a single screw extruder in accordance with the presently disclosed subject matter suitable for use in a method of the presently disclosed subject matter, e.g., for use in melt compounding mixtures of solids include PAN and a meltable solvent according to an embodiment of the presently disclosed subject matter.

DETAILED DESCRIPTION

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 meltspinning 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 meltcompounding 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.

I. DEFINITIONS

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 ₂ .

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 CH2=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 ₂ =CH-CN (i.e., CH ₂ =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)nC(=O)(CHOH) _m 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.

Lignocellulosic biomass include a variety of plants and plant materials, such as, but not limited to, papermaking sludge; wood, and wood-related materials, e.g., saw dust, or particle board, leaves, or trees, such as poplar trees; fibers from wood or non-wood plants; grasses, such as switchgrass and sudangrass; grass clippings; rice hulls; bagasse (e.g., sugar cane bagasse), jute; hemp; flax; kapok, coir, cotton, bamboo; sisal; abaca; hays; straws; miscanlhiis. corn cobs; corn stover; whole plant corn, bamboo, and coconut hair. In some embodiments, lignocellulosic biomass is selected from the group including, but not limited to, herbaceous material, agricultural residues, forestry residues, municipal solid wastes, waste paper, pulp and paper mill residues, or a combination thereof.

“Lignin” is a polyphenolic material comprised of phenylpropane units linked by ether and carbon-carbon bonds. The phenylpropane units are derived from precursor monolignols, such as, but not limited to, paracoumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. Lignins can be highly branched and can also be crosslinked. Lignins can have significant structural variation that depends, at least in part, on the plant source involved.

The term “cellulose” refers to a polysaccharide of P-glucose (i.e., 0-1,4-glucan) comprising P-(l-4) glycosidic bonds. The term “cellulosic” refers to a composition comprising cellulose.

The term “hemicellulose” can refer polysaccharides comprising mainly sugars or combinations of sugars other than glucose (e.g., xylose). Thus, xylan (polymerized xylose) and mannan (polymerized mannose) are exemplary hemicelluloses. Hemicellulose can be highly branched. Hemicellulose can be chemically bonded to lignin and can further be randomly acetylated, which can reduce enzymatic hydrolysis of the glycosidic bonds in hemicellulose.

The terms “glycosidic bond” and “glycosidic linkage” refer to a linkage between the hemiacetal group of one saccharide unit and the hydroxyl group of another saccharide unit.

As used herein, the term "fiber," refers to an elongated strand of material in which the length to width ratio is greater than about 10, greater than about 25, greater than about 50 or greater than about 100. A fiber typically has a round, or substantially round, cross section. Other cross-sectional shapes for the fiber include, but are not limited to, oval, square, triangular, rectangular, star-shaped, trilobal, pentalobal, octalobal, and flat (i.e., "ribbon" like) shape. The fiber can have any desired diameter, for example, thicker fibers (or “rods) can be chopped or pelletized, while thinner fibers can be used to prepare yarns or fabrics. In some embodiments, the fiber has a diameter of less than about 250 micrometers, less than about 200 micrometers, less than about 150 micrometers, less than about 100 micrometers, less than about 75 micrometers, less than about 50 micrometers, less than about 25 micrometers, or less than about 10 micrometers. In some embodiments, the fiber has a thickness of about 1 micron to about 250 micrometers. In some embodiments, the fiber has a thickness greater than about 250 micrometers. For example, thicker fibers or rods that can be chopped to provide pellets can have a thickness of a few hundred microns (e.g., about 300 micrometers, about 400 micrometers, about 500 micrometers, or about 750 micrometers) to a few millimeters (mm) (e.g., about 5 mm, about 10 mm, or about 25 mm). In some embodiments, the thicker fibers or rods can have a diameter of about 1 mm to about 5 mm (e.g., 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or about 5 mm). In some embodiments, the thicker fibers or rods can be chopped into pellets having a length of about 1 mm to about 5 mm (e.g., 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or about 5 mm).

The terms "monofilament fiber" and "monofiber" refer to a continuous strand of material of indefinite (i.e., not predetermined) length, while the term "staple fiber" refers to a discontinuous strand of material of definite length (i.e., a strand which has been cut or otherwise divided into segments of a predetermined length).

A "melt-spun fiber," as used herein, is a fiber produced by a melt-spinning process. Melt-spinning is a process whereby a melt is extruded through one or more dies, such as one or more die capillaries (e.g., a spinneret, for example) as molten filaments while simultaneously applying an extensional force which reduces the thickness of the molten filaments. The molten filaments solidify upon cooling below their melt temperature to form fibers. The term "melt spinning" encompasses stable fiber spinning (including short spinning and long spinning) and bulk continuous filament fiber. Melt spun fibers can optionally be cold-drawn.

The terms “melt-compounding” or “compounding” as used here refer to a process of melt blending materials, such as polymers with other additives. Melt-compounding typically involves both heating and mixing materials. In some embodiments, as used herein, the terms “melt-compounding” and “compounding” refer to a method of blending a mixture (e.g., a solids mixture) comprising polyacrylonitrile and one or more other components (e.g., a meltable solvent, lignin, or an additive) to provide a homogeneous or more homogeneous blended composition. In some embodiments, compounding further includes extruding the blended composition (e.g., the melted/compounded mixture of solids, which can also be referred to as the “melted/compounded resin” or “melted/compounded resin concentrate”). Thus, the term “melt-compounding” as used herein can encompass processes such as melt-extruding and melt-spinning. In some embodiments, the terms “meltcompounding” or “compounding” further include any techniques, that involve an apparatus, such as an extruder, capable of melting and mixing a mixture, such as but not limited to additive manufacturing techniques such as 3D printing.

The term “carbon fiber” refers to a fiber comprising 90 weight % (wt%) or more or 92 wt% or more carbon. Carbon fibers can be prepared by the thermal conversion of fibers with lower carbon content. The process to fabricate carbon fiber from lower content “carbon fiber precursor” fibers (e.g., PAN fiber or PAN/lignin fiber) can include “stabilizing” the precursor fiber, e.g., cyclizing or reorganizing the backbone chain into a series of rings, and then heating the stabilized precursor fiber under an inert atmosphere (e.g., argon or nitrogen) above 300°C (e.g., to about 300°C to about 1200°C or to about 1000°C to about 1700°C) to drive off hydrogen atoms. This can also be referred to as “carbonizing.” Further high temperature treatment or “graphitization” can be used to remove other non-carbon atoms (e.g., nitrogen), but can involve higher temperatures, e.g., about 1500°C to about 2800°C.

II. METHODS OF PREPARING FIBER, RELATED FIBERS AND OTHER COMPOSITIONS

As described above, acrylic fibers (e.g., fibers prepared from PAN homo- and copolymers) are typically solution spun due to chemical degradation near their melting temperature. Previous attempts at PAN melt-spinning have followed two general approaches: internal plasticizing through comonomers and/or external melt-depressing agents. For instance, the Eby theory of comonomer melting (where non-crystallizing comonomers enter the crystal lattice structure as point defects as opposed to being regulated to the amorphous phase) has been applied to PAN copolymers. This impregnation of defects to the crystal lattice reduced the melting point and heat of fusion, which can be interpreted as the measure of regularity and strength of the intermolecular dipolar bonding that stabilizes the lattice. ⁴ The melting point depression was found to be dependent on the molecular structure of the comonomer, where methyl acrylate, vinyl acetate, ethyl vinyl ether, vinyl bromide, vinylidene chloride, and vinyl chloride saw decreasing melt point depression constants, respectively. ⁸ Through the copolymerization of 10 mol% methyl acrylate (MA) with acrylonitrile (AN), melt flowability was achieved up to 50 kDa at 220°C. ⁹ At about 15 mol %, MA increased the melt flowability molecular weight to 100 kDa. However, at 220°C, those copolymers exhibited distinctly higher zero-shear viscosities (-100 MPa/s) than an extrudable-grade AN-derived copolymer, sold under the tradename BAREX™ (INEOS Barex, Delaware City, Delaware, United States of America), containing 65 mol % AN, 25 mol % MA, and 10 mol % elastomer (-70 MPa/s at 180°C), indicating difficulties in extrusion. As a result, melt spinning was not performed for these copolymers.

External melt depressing agents have also been investigated to plasticize PAN for melt spinning, such as with the incorporation of propylene carbonate (PC), water, and ionic liquids. ¹⁰ ' ¹² PAN copolymer (8.1 mol % MA, Mn= 34,000) spun with 22.5 wt % PC resulted with a tensile strength of 370 MPa, young's modulus of 9.1 GPa, and fineness of 15.7 pm when spun at 175°C at a take-up of 600 m/min. ¹¹ Higher molecular weight led to higher tensile strength and Young's modulus, but an upper limit of 46,000 g/mol found no melt- spinnable PAN/PC mixture. Propylene carbonate is a good solvent for PAN at elevated temperatures, but a bad solvent at room temperature. This relative incompatibility could inhibit the plasticization of higher molecular weight PAN to a degree where melt spinning is unachievable. PAN of M _v = 82,000 g/mol was melt spun with 23 wt % water at by first melting at 170 °C followed by supercooled melt spinning at 150°C. ¹⁰ The resulting fibers achieved a tenacity of 4.5 g/den, elongation of 12.5 %, and modulus of 50 g/den, but displayed micropores. Moreover, water vapor emission was evident during the spinning process.

Dimethyl sulfone (DMSO-2), also known as methyl sulfonylmethane (MSM) is a solid at room temperature, having a melting point at about 109°C and a boiling point at about 248°C. As described herein, DMSO-2 can be used as meltable solvent for PAN. In some embodiments, DMSO-2 can be used to provide a melting point depression in mixtures of solids comprising PAN and improved melt-spinning processability for higher molecular weight PAN. Additionally, as DMSO-2 has similar solubility parameters as DMSO, PAN- kraft lignin (KL) melt-spinning can be performed, e.g., with lignin incorporated in the PAN fibers to reduce the cost of the resulting fiber, which can be used for carbon fiber conversion. Accordingly, the presently disclosed subject matter describes, in some embodiments, the melt-spinning processability of PAN/DMSO-2 and PAN-KL/DMSO-2 powder blends in bench scale, then follows with pilot scale PAN/DMSO-2 melt-spinning. Additionally, suitable washing time for DMSO-2 removal of as-spun (AS) PAN/DMSO-2 fibers is described, along with its impact on mechanical and morphological properties.

Accordingly, in some embodiments, the presently disclosed subject matter provides a method of preparing a fiber (e.g., fiber comprising PAN or a blend of PAN and lignin), wherein the method comprises: (a) preparing a mixture of solids comprising PAN and a meltable solvent; and (b) melt-spinning said mixture of solids; thereby preparing the fiber. In general, melt-spinning involves melting a polymer into a viscous liquid and extruding it though a spinneret to create a fiber. Melt-spinning can also be considered as a form of meltextrusion. Thus, the terms “melt-spinning” and “melt-extrusion” can be used interchangeably herein.

In some embodiments, the mixture of solids can further comprise lignin. Thus, in some embodiments, (a) comprises preparing a mixture of solids comprising PAN, lignin, and a meltable solvent. Lignin is widely available, inexpensive, and renewable. Lignin is a formed from mainly three types of phenylpropane monolignols: paracoumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. Lignin polymers can range in molecular weight depending on source, i.e., between species of plant. When still in its natural state, lignin is referred to as “protolignin.” It has been reported that the types of plants also have an impact on the protolignin structures: softwood lignin is based primarily on coniferyl alcohol and lignin from hardwoods and grasses are derived from a blend of all three main types of monolignols. Because of these differences, pulp from different mills can contain different lignin types; a mill producing soft paper products such as tissue paper primarily uses hardwoods, so the lignin by-product will reflect the hardwood source. Typically, softwoods and eucalypts contain the highest percentages of lignin.

With improved recovery methods and an increased demand in production for the paper pulping industry, lignin can be easily recovered and utilized as an inexpensive and widely available bioresource. For over a century, the paper pulping industry has been using the same recovery equipment to handle the runoff for energy, however with a growing demand for solid lignin and newer recovery techniques, lignin can be available at low cost.

Most pulping is conducted with the Kraft process, a chemical pulping method that loads the product with sulfur in order to increase the strength of the final product. Kraft pulping is known to produce pulp with high strength, simple liquor recovery, and versatility with different pulp sources (such as softwood vs hardwood). Sodium hydroxide and sodium sulfide in the pulp break own the lignin macromolecules into smaller, water and alkaline soluble parts. Sulfites have also been used to further increase the sulfur content and reduce lignin, but often the gain is minimal or sometimes detrimental with loss of strength as a result of acidic degradation. Through experience, industry has streamlined the process to have the highest yield and most efficient processing times. Temperature is often kept between 150°C and 165°C inside pressurized vessels in order to have the most efficient and consistent delignification possible, though truly homogenous delignification is not currently possible. “Black liquor” containing broken down cellulose, hemicellulose, lignin, inorganics, and other waste materials is then recovered, concentrated, and then used as fuel. This black liquor is the primary source of recovered lignin, where it is in a reduced state and has a wide range of molecular weights, often with 2 to 3 kDa molecular weights. Processing the black liquor to extract lignin has become even more efficient due to increased demand from the fact that the paper mills often run at the rate of lignin biofuel recovery.

An alternative method to achieve fiberization of the pulp from chips is known as steam explosion. Wood chips are subjected to temperatures around 285°C at 3.5 MPa, then rapidly pressurized to 7 MPa. The chips are then ejected into 1 atm of pressure, resulting in explosive depressurization that defibrillates the cellulose portions, allowing better access for hydrolysis to occur in both the cellulose and hemicellulose zones. As a result, cracks and total defibrillation for the wood fibers is achieved. Acids have been used to increase the rate of hydrolysis of the hemicellulose as well; however, no chemicals are actually required except for water. This method is environmentally friendly due to the lack of inherent acid processing that degrades equipment and could pose a threat to workers, however the lignin recovered from this method is poorly solubilized and is often more broken down to be utilized in post processing. The molecular weight of lignin derived from steam explosion can range between 0.8 kDa to 2.0 kDa.

Lignin is considered a waste product, so processing was originally designed to remove lignin and hemicellulose in order to make paper pulp. However, Organosolv processing was developed to remove each fraction of the feedstock from each other. It utilizes organic solvents such as acetone, ethanol, methanol, and organic acids to extract lignin and depolymerize the cross-linked hemicellulose. As a result, Organosolv lignin is much higher in purity than Kraft and steam explosion lignin, as well as having a low molecular weight, narrow distribution, and low sulfur content. To separate the cellulose in a solid phase, warm organic solvent between 130°C and 200°C is added to the feedstock. Black liquor containing lignin and hemicellulose is produced as a liquid phase. The black liquor is then separated into an aqueous phase and an organic phase. This organic phase is comprised mainly of lignin, which can then be recovered through distillation. While volatile organic solvents are indeed used, they can be distilled off for reuse and to remove the lignin easily. However, organic solvents are relatively expensive and are sensitive to temperature and atmospheric pressure, narrowing processing parameters which leads to increasing expenses and higher required initial capital.

Thus, in some embodiments, the lignin included in the mixture of solids of the presently disclosed methods is derived from a hardwood or softwood feed stock. In some embodiments, the lignin comprises or consists of kraft lignin (KL). In some embodiments, the lignin comprises or consists of kraft softwood lignin. In some embodiments, the mixture of solids can comprise up to about 30 wt% lignin. In some embodiments, the mixture of solids can comprise about 1 wt% to about 30 wt% lignin (e.g., about 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, or about 30 wt% lignin). In some embodiments, the mixture of solids comprises about 10 wt% lignin. In some embodiments, the ratio of lignin to PAN is about 1 :4 to about 1 : 1. Inclusion of the lignin can lower material costs for the fiber and improve the energy requirements to convert the fiber into carbon fiber.

The term “meltable solvent” refers to a compound that is solid at room temperature but that melts below temperatures used for melt-spinning (e.g., temperatures below about 100°C to about 230°C). Thus, in some embodiments, the meltable solvent is a compound that has a melting point above about 25°C (or about 30°C or about 40°C) but that is about 230°C or less. Suitable meltable solvents for use according to the presently disclosed subject matter can also have a flash temperature or boiling temperature below temperatures used for melt-spinning (e.g., greater than about 230°C). In addition, suitable meltable solvents are also those that are able to mix with the PAN (or PAN and lignin) to provide a homogenous solids mixture during compounding. In some embodiments, the meltable solvent comprises or consists of DMSO-2 and/or a choline salt. Suitable choline salts that can be used as meltable solvents include, but are not limited to, choline acetate (Tm = 81 °C), choline isobutyrate (Tm = 68°C), choline isovalerate (Tm = 61 °C), and choline 2- methylbutyrate (Tm = 90°C). In some embodiments, an imidazolium salt (e.g., l-ethyl-3- methylimidazolium acetate salt or a l-butyl-3-methylimidazolium salt) can be used as an alternative solvent for melt-spinning (e.g., in combination with or in place of the meltable solvent). While these compounds can be liquid at room temperature, they have high flash points, that can make them suitable for use in melt-extrusion/melt-spinning.

In some embodiments, the meltable solvent comprises or consists of DMSO-2. In some embodiments, the mixture of solids comprises about 40 wt% to about 60 wt% (e.g., about 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, 56 wt%, 58 wt%, or about 60 wt%) DMSO-2. In some embodiments, the mixture of solids can include DMSO-2 as a meltable solvent and can further comprise an imidazolium salt. In some embodiments, the mixture of solids is free of an imidazolium salt. Alternatively, in some embodiments, the mixture of solids can include an imidazolium salt in place of the meltable solvent (e.g., the DMSO-2).

In some embodiments, the preparation of the mixture of solids and/or melt-spinning is performed substantially in the absence of water or a hydrate of the PAN. Thus, typically, the mixture of solids is prepared in the absence of adding any water or in the absence of adding water to reduce the PAN melting temperature. In some embodiments, (a) comprises preparing a mixture of solids comprising PAN and a meltable solvent, wherein the mixture is substantially free of water or a PAN hydrate. The terms “substantially in the absence of’ and “substantially free of’ refer to compositions comprising about 1 wt% or less of a recited material (e.g., about 1 wt% or less, about 0.5 wt % or less, about 0.25 wt% or less, about 0.1 wt% or less, or about 0.05 wt% or less or a recited material). In some embodiments, the DMSO-2 is anhydrous DMSO-2 and/or the PAN is dried (e.g., in an oven for a period of time and/or at a temperature high enough to evaporate water) prior to preparation of the mixture of solids to remove any water.

The PAN included in the mixture of solids can include one or more homopolymers (i.e., one or more polymers (where each polymer has a different average molecular weight) prepared by polymerization of acrylonitrile (AN)) and/or one or more copolymers (prepared by the copolymerization of AN and up to about 15 mole (mol) % of one or more comonomers). Comonomers for the presently disclosed PAN polymers include vinyl comonomers, such as, but not limited to, methyl acrylate (MA), vinyl acetate, ethyl vinyl ether, vinyl bromide, vinylidene chloride, itaconic acid, and vinyl chloride. In some embodiments, the mixture of solids comprises a PAN copolymer, wherein said copolymer is a copolymer of AN and MA. In some embodiments, the PAN copolymer is prepared from a mixture of monomers consisting of AN and MA, wherein the MA comprises about 1 mol% to about 15 mol% (e.g., about 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, 11 mol%, 12 mol%, 13 mol%, 14 mol%, or about 15 mol%) of the monomers in the mixture of monomers. In some embodiments, the mixture of monomers comprises about 8 mol% MA.

In some embodiments, one or more of the PAN polymers in the mixture of solids (or all of the PAN polymers in the mixture of solids) has a number average molecular weight (Mn) of about 25,000 kDa or more, 50,000 kDa or more, or 75,000 kDa or more. In some embodiments, the PAN has a viscosity average molecular weight (M _v ) of about 50 kilograms per mole (kg/mol) or more. In some embodiments, the PAN has a M _v of about 50 kg/mol to about 250 kg/mol (e.g., about 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, or about 250 kg/mol), In some embodiments, the PAN has a M _v of about 80 kg/mol.

In some embodiments, the PAN comprises a polymer or copolymer of a biomass- derived AN. For example, the AN monomer polymerized or copolymerized to form the PAN can be prepared from propionic acid (PA), isopropanol (IPA), and/or 3- hydroxypropionic acid (3-HPA) or an ester thereof, wherein said PA, IPA, and/or 3-HPA is product of the conversion of biomass-derived sugars. AN can also be prepared from lactide. Thus, in some embodiments, a biomass-derived AN can be used to provide a PAN for the presently disclosed mixture of solids as a renewable carbon source.

In some embodiments, the PAN comprises a polymer or copolymer of synthetic AN, i.e., AN derived from a petroleum-based source. In some embodiments, the PAN comprises PAN prepared from both biomass-derived AN and synthetic AN.

In some embodiments, some or all of the PAN is recycled PAN, i.e., PAN derived from a previous manufactured PAN article. Thus, in some embodiments, the presently disclosed subject matter provides a method of recycling PAN from pre- or post-consumer waste, e.g., to provide a carbon fiber precursor. In some embodiments, the PAN can include both biomass-derived AN and PAN derived from pre- or post-consumer waste. Accordingly, the presently disclosed methods can be applied to biomass-derived AN and/or PAN derived from pre- or post-consumer waste.

In some embodiments, the mixture of solids can comprise one or more additives. For example, the additives can be selected from additives known in the art of spin-melting fibers, such as, but not limited to, plasticizers, antipasticizers, fillers, extenders, slip agents, colorants (e.g., dyes, inorganic pigments), delusterants, flame retardants, and anti-oxidants. In some embodiments, the mixture of solids further comprises a plasticizer. Suitable plasticizers include, but are not limited to, phthalates (e.g., dioctyl phthalate (DOP)); biodegradable citrates (e.g., acetyl triethyl citrate or tributyl citrate); glycerol; organic acids (e.g., tartaric acid or mucic acid); and mixtures thereof.

In some embodiments, the additive is a filler. In some embodiments, the filler is a solid salt, such as lithium chloride or zinc chloride. In some embodiments, the meltable solvent is DMSO-2 and the mixture of solids can further include zinc chloride and/or lithium chloride (e.g., about 5% to about 12% of chloride salt compared to the weight of the DMSO- 2).

In some embodiments, the mixture of solids can include at least one antiplasticizer. Various antiplasticizing molecules have been used in fiber preparation. Antiplasticizers include small, rigid molecules comprising polar constituents including halogen, nitrogen, or oxygen atoms, as well as alkane oils. In some embodiments, the antiplasticizer is glucaric acid. In some embodiments, the mixture of solids can comprise about 0.1 to about 5 wt% of one or more antiplasticizers.

In some embodiments, providing the mixture of solids can involve meltcompounding, e.g., using a single screw extruder, a twin-screw extruder or any other device that can melt and mix the solids. In some embodiments, the melt-compounded mixture can be extruded in a rod that is chopped or pelletized prior to melt-spinning. Alternatively, the melt-compounding can be performed as part of the melt-spinning, so that the compounded melt is fed directly into a spinneret or other extrusion head suitable for extruding fibers of a desired thickness. Alternatively or additionally, provision of the mixture of solids can comprise grinding, e.g., using a high-speed mixer while dry (e.g., at 500 RPM or more). In some embodiments, the melt-spinning can be performed by melting the mixtures of solid (e.g., pellets of previously melt-compounded mixtures) in a multi-zone extruder that feeds into a spinning pack and extruding the melt to form a fiber.

In some embodiments, step (a) comprises melt-compounding the mixture of solids to provide a compounded mixture of solids (e.g., using a twin-screw extruder). In some embodiments, the melt-compounding is performed at a temperature between about 90°C and about 180°C (e.g., about 90°C, about 100°C, about 110°C, about 120°C, about 130°C, about 140°C, about 150°C, about 160°C, about 170°C or about 180°C). In some embodiments, the melt-compounding is performed using a multi-zone extruder where the mixture is progressively introduced into higher temperature zones (e.g., each between about 90°C and about 180°C). In some embodiments, the melt-compounded material is extruded in the form of a rod and chopped to provide pellets. In some embodiments, the melt- spinning of step (b) is performed by melt-extrusion (e.g., of the pellets provided after the melt-compounding) at a temperature of about 150°C to about 220°C (e.g., about 150°C, about 160°C, about 170°C, about 180°C, about 190°C, about 200°C, about 210°C, or about 220°C) In some embodiments, the melt-spinning is performed by melt-extrusion at a takeup speed of up to about 100 meters per minute (m/min). In some embodiments, the take-up speed is about 40 to about 100 m/min (e.g., about 40, 50, 60, 70, 80, 90, or about 100 m/min).

While inclusion of the meltable solvent can improve compounding and meltspinning, it can be desirable to remove the meltable solvent after the fibers are formed. Thus, in some embodiments, the presently disclosed method further comprises removing the meltable solvent after step (b). For example, the meltable solvent can be removed by washing, e.g., by submersing the fiber in a water bath or by pulling the fiber through a water bath under tension. The water of the water bath can be at an elevated temperature, e.g., up to 100°C. In some embodiments, the water bath is at a temperature between about 60°C and about 100°C (e.g., about 60, 65, 70, 75, 80, 85, 90, 95, 98, 99, or about 100°C). In some embodiments, the water bath has a temperature of about 95°C. In some embodiments, the fiber has a dwell time in the water bath of about 10 seconds to about 300 seconds (e.g., about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or about 300 seconds. In some embodiments, the fiber has a dwell time in the water bath of about 150 seconds.

In some embodiments, removing the solvent can decrease the linear density and or cross-sectional area of the fibers. In some embodiments, removing the solvent deceases the number and/or size of microvoids in the body of the fiber. In some embodiments, removing the solvent increases the tenacity and/or modulus of the fibers. In some embodiments, removing the solvent decreases the % strain at break of the fibers.

In some embodiments, fiber drawing can occur during the washing. Alternatively, fiber drawing (e.g., in air at an elevated temperature, such as at about 80°C to about 220°C) can be performed after spinning but prior to washing and/or can be performed after washing.

Referring now to Figures 9A-9E, are systems in accordance with the presently disclosed subject matter, which are suitable to carry out a method of the presently disclosed subject matter. For instance, Figure 9A shows twin-screw extruder 104 suitable for use in melt-extruding or melt-compounding mixtures comprising PAN and a meltable solvent (or PAN, lignin and a meltable solvent). Mixture M (comprising PAN, a meltable solvent and optionally one or more other components, such as lignin or an additive) can be inserted in hopper openings 109 in direction Al and driven through internal space 126 of extruder 104 by screws 122, to produce filament F from outlet 107. As shown in Figure 9A, twin-screw extruder 104 includes motor 121, which can drive twin screws 122 of extruder 104 rotationally. Extruder 104 can be configured to provide zones that are operable to melt, mix, and provide homogenization to the mixture M so that a filament F can be extruded in the direction of arrow A3. In some embodiments, melting zone MZ, mixing zone MX, and homogenization zone HG occur sequentially beginning from motor 121 and proceeding towards outlet 107 of extruder 104. After filament F exits twin-screw extruder 104 from outlet 107 in direction A3, it can be collected, e.g., on a spool, cut into desired lengths or chopped into pellets for further compounding or melt-spinning later.

Figure 9E shows single screw extruder 102 suitable for use in melt-extruding or melt-compounding mixtures comprising PAN and a meltable solvent. Mixture M (comprising PAN and a meltable solvent) can be inserted in hopper opening 108 in direction Al and driven through the internal space 124 of extruder 102 by screw 120, to produce a filament F from outlet 107. As shown in Figure 9E, single screw extruder 102 includes motor 121, which can drive screw 120 of extruder 102 rotationally in direction A4. As with extruder 104 of Figure 9A, extruder 102 of Figure 9E can be configured to provide zones that are operable to melt, mix, and provide homogenization to the mixture M so that a filament F can be extruded in the direction of arrow A3. In some embodiments, melting zone MZ, mixing zone MX, and homogenization zone HG occur sequentially beginning from motor 121 and proceeding towards outlet 107 of extruder 102. After filament F exits extruder 102 from outlet 107 in direction A3, it can be collected, e.g., on a spool, cut into desired lengths or chopped into pellets for further compounding or melt-spinning later.

Homogenization can be improved by the number of zones or the number of passes through an extruder (e.g., a single screw extruder of Figure 9E or a twin-screw extruder of Figure 9A). Homogenization is indicated by extrusion of a smooth rod of extrudate from the extruder. For instance, 2-3 passes through the extruder can be used for homogenization, but, in some embodiments pellets can be sufficient homogenized after 1 pass through an extruder in the form of a Barbender compounder, having 4 zones, but additional passes can be considered. The temperature can gradually increase with each zone. For example, in some embodiments, zone 1 can be at 140°C, zone 2 at 160°C, and zones 3 and 4 of an extruder in the form of a Barbender compounder can be at temperatures of 180°C; +/- 15°C for each zone. Similar zone temperatures can be used for melt spinning, but around + 10°C for each respective zone temperature. Non-limiting, representative temperature ranges, mixing rates, and other parameters are disclosed elsewhere herein.

In some embodiments, fibers of the presently disclosed subject matter can be melt- spun using a system such as system 100 of Figure 9D. System 100 comprises an extruder 102, which by way of non-limiting example can be a single screw extruder as described in Figure 9E or a twin-screw extruder as shown in Figure 9A. Extruder 102 can further comprise a hopper 108 (which can optionally be a double hopper (i.e., a hopper with two openings) as shown in Figure 9 A) and a mixture M in accordance with the presently disclosed subject matter (e.g., a mixture of PAN and a meltable solvent) can be fed into hopper 108 in the direction of arrow Al. An airpath device 110 follows extruder 102 in line and a filament F extruded from outlet 107 of extruder 102 travels over airpath device 110 in the direction of arrow A2. Air path device 110 can be used to help solidify the filament. Examples of the extruder and the airpath are commercially available from under the tradename FILABOT® (Triex, LLC, Barre, Vermont, United States of America). The filament F is wound on take-up roller 112. A representative example of a take-up roller 112 is also commercially available under the tradename Filabot Spooler: Precision Filament Winder (Triex, LLC, Barre, Vermont, United States of America). In some embodiments, filament F is drawn across air path 110 and and taken upon by motorized reels 114 and 116 and collected on a spool 118 of take-up roller 112. The speed of the take-up roller is adjusted to tune the diameter of collected filament. As the take-up speed for continuous filament increases, filament diameter decreases.

Figure 9B shows apparatus 130 suitable for preparing fibers (including bicomponent fibers) of the presently disclosed subject matter. Apparatus 130 includes two extruders 132 and 134, which can be used for two different mixtures, i.e., one for a first mixture of solids corresponding to the core of a bicomponent fiber, and one for the second mixture of solids corresponding to the sheath of a bicomponent fiber. Extruders 132 and 134 can independently be single screw or twin-screw extruders, such as an extruder as shown in Figure 9A or 9E. Thus, in some embodiments, as shown in Figure 9B, each of extruders 132 and 134 can include three zones, MZ, MX, and HG, sequentially arranged such that zone HG is located adjacent to exit pipes 135 of extruders 132 and 134. The flow of melted/compounded mixture of solids in exit pipes 135 can be controlled by gear pumps 136 and supplied via pipes 137 to spinning pack 140. Figure 9C shows a cross-sectional view of exemplary spinning pack 140 of apparatus 130 of Figure 9B. As shown in Figure 9C, spinning pack 140 can include multiple openings for entry of melted/compounded mixtures of solids from pipes 137. For example, spinning pack 140 can include a central opening 141 for melted/compounded mixture of solids Ml corresponding to the core of a bicomponent fiber supplied from one of extruder 132 or 134 of apparatus 130. Spinning pack 140 can further include two or more side/peripheral openings 142 for entry of melted/compounded mixture of solids M2 corresponding to the sheath of a bicomponent fiber supplied from the other of extruder 132 or 134. Melted/compounded mixture of solids M2 can then fill in around a central shaft of melted/compounded mixture of solids Ml at or near exit 143 of spinning pack 140 to form bicomponent fiber F’ as it exits spinning pack 140. Continuing with Figure 9B, bicomponent fiber F’ can be collected on take-up device 150 (e.g., a take-up spool) turning in direction A4.

As noted above, the air path in Figure 9D can serve to help solidify the fibers. Thus, in some embodiments, the air path can be used, e.g., where it is not necessarily desired to remove a meltable solvent. Alternatively, solvent baths can be used to solidify the fibers. In some embodiments, the solvent bath can be used to remove a meltable solvent. In some embodiments, an air path can be used to solidify the fiber prior to exposing the fiber to a solvent bath, e.g., to remove meltable solvent.

In some embodiments, a spun or extruded fiber can be drawn through a wash bath (e.g., using rollers) for a desired treatment, such as to remove molten solvent. The rollers can keep the fiber under tension while the molten solvent is removed so that the fiber can retain its shape during the removal, even if the non-solvent components (e.g., PAN or lignin) soften in the bath. Baths and other related components for bath treatment of fibers are known in the art and commercially available.

In some embodiments, the fibers can be directed to a pelletizer to form pellets from the fiber and the pellets can be collected in a collector. Suitable pelletizers for preparing pellets of the presently disclosed fibers are known in the art and commercially available. The pellets can be used, for example, as engineering plastics. It is further noted that a pelletizer and collector can also be implemented with an extruder and air gap as shown in Figure 9D, as yet a further embodiment. Indeed, any configuration of system components as would be apparent to one of ordinary skill in the art upon a review of the present disclosure is provided herein and falls with scope of the presently disclosed subject matter. Additional examples of commercially available equipment that can be employed in accordance with the presently disclosed subject matter include a Brabender compounder (C.W. Brabender Instruments, Inc., South Hackensack, New Jersey, United States of America) or a LIST knead reactor (LIST Technology AG, Anisdorf, Switzerland) (which can be employed for pelletization of a fiber), Hills melt extrusion screw extruders (Hills Inc., West Melbourne, Florida, United States of America) (which can process pellets into fibers), and Engel Injection Molding Machinery (Engel Machinery Inc., USA (York, Pennsylvania, United States of America). In some embodiments, additive manufacturing techniques and equipment can be employed in the methods of the presently disclosed subject matter such as those from 3D Systems (Rock Hill, South Carolina, United States of America) for 3D printers for additive manufacturing.

In some embodiments, the PAN or PAN/lignin fibers can be used as acrylic fibers. In some embodiments, the acrylic fibers can be used in preparing fabrics for clothing or upholstery. In some embodiments, the acrylic fibers can be used in carpets or other flooring applications. In some embodiments, the acrylic fibers can be used in construction, as building materials.

As noted hereinabove, in some embodiments, the PAN or PAN/lignin fibers prepared by the melt-spinning can be used as precursors for carbon fibers. Methods of making carbon fibers from PAN-containing or other types of precursor fibers are known in the art. Thus, in some embodiments, the method can further comprise stabilizing (or cyclizing) the PAN or PAN/lignin fibers. Stabilizing can comprise heating the fiber (e.g., in air) to a temperature between about 90°C and about 300°C. In some embodiments, the method can further comprise carbonizing the PAN or PAN/lignin fibers. Carbonization can be performed by heating the fiber under an inert gas atmosphere (e.g., nitrogen or argon gas) to a temperature between about 300°C and about 1700°C. In some embodiments, the method further comprises graphitizing the fiber (i.e., the carbonized fiber). In some embodiments, the graphitizing comprises heating the carbonized fibers to a temperature of about 1500°C to about 2800°C. In some embodiments, graphitizing comprises heating the carbonized fibers to a temperature above about 1700°C, above about 2000° V, above about 2200°C, or above about 2400°C.

In addition to providing methods of preparing fibers, the presently disclosed subject matter further relates to the fibers themselves, as well as to products prepared from the fibers. The presently disclosed fibers can be monocomponent or multicomponent. The term “component” as used herein with regard to fibers is defined as a separate part of a fiber that has a spatial relationship to another part of the fiber. Thus, the term “multi-component” as used herein is defined as a fiber having more than one separate part in spatial relationship to one another. The term multi-component includes “bicomponent”, which is a fiber having two separate parts in a spatial relationship to one another. Monocomponent fibers can be provided having any desirable geometry, e.g., circular or trilobal cross-sectional geometries, and/or as hollow fibers. The different components of multi-component fibers can be arranged in substantially distinct regions across the cross-section of the fiber and extend continuously along the length of the fiber. Bicomponent and multicomponent fibers of the presently disclosed subject matter can be in a side-by-side, sheath-core, segmented pie, ribbon, or islands-in-the-sea configuration, or in any combination thereof. In some embodiments, the bi- or multi-component fiber can include a sacrificial layer or component. Such fibers can be used, for instance, to provide a microdenier fiber. In some embodiments, the fiber can have a splittable segmented pie configuration comprising sacrificial wedges or an islands-in-the-sea configuration comprising a sacrificial sea or sacrificial islands. The sacrificial components can be polymers that can be removed using an aqueous solution and/or a caustic solution. Suitable sacrificial components include, but are not limited to, polylactic acid (PLA) water-soluble polyesters, and polyvinyl alcohol-based polymers. In some embodiments, the fiber comprises a sheath-core configuration wherein the sheath can be continuous or non-continuous around the core. The fibers of the presently disclosed subject matter can have different cross-sectional geometries that include, but are not limited to, round, elliptical, star shaped, square, triangular, rectangular, and irregular shapes. Thus, in some embodiments, the mixture of solids can be co-extruded with one or more additional mixture of solids, wherein each mixture can form of a fiber component.

Accordingly, in some embodiments, the presently disclosed subject matter provides an acrylic (i.e., a PAN) fiber or an acrylic/lignin (i.e., a PAN/lignin) fiber. In some embodiments, the fiber is a carbon fiber precursor. In some embodiments, the presently disclosed subject matter provides a melt-spun acrylic fiber (e.g., a melt-spun carbon fiber precursor and/or a PAN fiber or a PAN/lignin fiber). In some embodiments, the presently disclosed subject matter provides a carbon fiber prepared from the melt-spun carbon fiber precursor (i.e., a melt-spun PAN or PAN/lignin fiber). In some embodiments, the fiber (e.g., the carbon fiber precursor) comprises about 30 wt% to about 50 wt% lignin (e.g., about 30 wt%, about 35 wt%, about 40 wt%, about 45 wt%, or about 50 wt% lignin). In some embodiments, the carbon fiber precursor fiber has a diameter of about 50 micrometers or less (e.g., about 20 micrometers to about 50 micrometers). In some embodiments, the carbon fiber precursor fiber has a diameter of about 15 micrometers or less (e.g., about 1 micrometers to about 15 micrometers or about 5 micrometers to about 10 micrometers).

The carbon fibers prepared from the instant acrylic fibers can be used in a wide variety of applications, such as textiles, microelectrodes, and for making carbon fiber composites, e.g., for use as vehicle parts in the automotive and aviation industries. Thus, in some embodiments, the carbon fibers can be embedded in a polymeric matrix to provide a carbon fiber composite. In some embodiments, the precursor fibers can be used without carbonization, e.g., as acrylic fibers for use in the outdoors and/or home furnishing industries.

In some embodiments, the presently disclosed subject matter provides a composition comprising PAN and a meltable solvent. In some embodiments, the composition further comprises lignin. In some embodiments, the meltable solvent comprises or consists of DMSO-2. In some embodiments, the composition comprises about 40 wt% to about 60 wt% DMSO-2 (e.g., about 40 wt%, about 42 wt%, about 44 wt%, about 46 wt%, about 48 wt%, about 50 wt%, about 52 wt%, about 54 wt%, about 56 wt%, about 58 wt%, or about 60 wt% DMSO-2). In some embodiments, the composition comprises up to about 30 wt% lignin (e.g., KL, such as kraft softwood lignin). In some embodiments, the composition comprises about 10 wt% lignin. In some embodiments, the composition further comprises a filler or an antiplasticizer. In some embodiments, the composition is a homogenous blend. In some embodiments, the composition is provided in pellet form. In some embodiments, the composition is melt-compounded.

In some embodiments, the presently disclosed subject matter provides a melt- compounded mixture comprising PAN and a meltable solvent. In some embodiments, the melt-compounded mixture further comprises lignin. In some embodiments, the meltable solvent comprises or consists of DMSO-2. In some embodiments, the melt-compounded mixture comprises about 40 wt% to about 60 wt% DMSO-2 (e.g., about 40 wt%, about 42 wt%, about 44 wt%, about 46 wt%, about 48 wt%, about 50 wt%, about 52 wt%, about 54 wt%, about 56 wt%, about 58 wt%, or about 60 wt% DMSO-2). In some embodiments, the melt-compounded mixture comprises up to about 30 wt% lignin (e.g., KL, such as kraft softwood lignin). In some embodiments, the melt-compounded mixture comprises about 10 wt% lignin. In some embodiments, the melt-compounded mixture further comprises a filler or an antiplasticizer. In some embodiments, the melt-compounded mixture is provided in pellet form.

EXAMPLES

The following Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter.

General Materials and Methods

Polyacrylonitrile (a copolymer of a monomer mixture comprising 92% acrylonitrile (AN) and 8% methyl acrylate (MA)) with a viscosity average molecular weight of 80,000 g/mol was kindly donated by Dolan GmbH (Kelheim, Germany). BioPiva 100 Kraft softwood lignin (KL; < 2% ash content) sold under the tradename BIOPIVA™ 100 (UPM- Kymmene Corporation, Helsinki Finland) was kindly donated by UPM Biochemicals (Helsinki, Finland). Dimethyl sulfone (DMSO-2) was purchased from Bulk Supplements (Henderson, Nevada, United States of America).

Thermogravimetric analysis (TGA) was performed with a TA Discovery TGA 550 (TA Instruments, New Castle, Delaware, United States of America) purged with air at a heating rate of 10°C. Differential TGA (DTGA) was calculated through Origin software (Originlab Corporation, Northampton, Massachusetts, United States of America).

EXAMPLE 1

Bench Scale Compounding and Melt Spinning

60:40 (w/w) PAN:DMSO-2 was blended in a conventional blender and sifted through a 16x16 screen mesh. The powder blend was processed using a FILABOT® EX2 extruder (Triex LLC, Barre, Vermont, United States of America) with a 0.75 mm capillary at a temperature of 180°C, quenched with air, and manually pelletized. The pellets were loaded again to the FILABOT® EX2 extruder with a 0.75 mm capillary at a temperature of 180°C and taken up at 15 m/min to form neat as-spun (AS) fiber.

60:40 (w/w) PAN-KL:DMSO-2 powder blends were also processed with the same procedure with the PAN-KL blend at a 3 : 1 (w/w) PAN:KL ratio. The kraft lignin was dried in a 70°C oven for at least 24 hours prior to spinning.

EXAMPLE 2

Washing Time Determination

Bundles of bench scale PAN/DMSO-2 as-spun (AS) filaments were submerged in 95°C water for time intervals of 10, 30, 60, 150, and 300 seconds. Fourier Transform Infrared (FTIR) analysis was performed using an iS50 spectrometer (Thermo Fisher Scientific, Waltham, Massachusetts, United States of America) with built in attenuated total reflection (ATR) diamond crystal at 32 scans and resolution of 4 cm' ¹ . IR spectra ranging from 400-2400 cm' ¹ were normalized at a wavelength of 2242 cm' ¹ which correlates with the nitrile C=N stretch peak.

EXAMPLE 3

Pilot Scale Compounding and Melt Spinning

Pilot scale compounding of the 60:40 (w/w) PAN:DMSO-2 powder blend was conducted using a C.W. Brabender Single Screw Extruder (C.W. Brabender Instruments, Inc., South Hackensack, New Jersey, United States of America) with zone 1-4 temperatures of 150, 170, 180, and 180°C, respectively, at 15 RPM. The melt was extruded through a single capillary die of 10 mm in diameter, quenched with room temperature air for rapid solidification, and pelletized through a mechanical chipper.

Pilot scale melt spinning was conducted using a Hills Bi-Component Filament Machine (Hills, Inc., West Melbourne, Florida, United States of America) with zone 1-4 temperatures of 150, 160, 170, 180°C and spin pack temperature at 220°C at 20 RPM. The melt was extruded through a 72-filament die with capillary diameter of 200 pm and taken up at 40, 80, and 100 m/min.

EXAMPLE 4

Imaging, Mechanical Testing, and X-Ray Diffraction Studies of Fibers

Cross-sectional samples were prepared by feeding the sample and Nylon 6,6 filler through a cork and sliced with a razor blade. Au/Pd sputter coating was applied to the samples prior to scanning electron microscopy (SEM) imaging by a Hitachi TM-4000 microscope (Hitachi, Tokyo, Japan). The cross-sectional areas were determined through ImageJ software.

In accordance with ASTM Standard D3822/D3822M (Standard Test Method for Tensile Properties of Single Textile Fibers), mechanical testing was performed with a gauge length of 25.4 mm and at a rate of 15.0 mm/min through an MTS Q-Test 5 and TestWorks software (MTS Systems Corporation, Eden Prairie, Minnesota, United States of America).

One dimensional (1-D) X-ray diffraction (XRD) was performed with a X-Ray diffractometer sold under the tradename SMARTLAB® (Rigaku Americas Corporation, The Woodlands, Texas, United States of America) at 40 kV operating voltage, 44 mA current, and a CuK-a beam with k = 0.154 nm over a 5-50°scan range.

EXAMPLE 5

Discussion of Examples 1-4

TGA and DTGA Analysis of Raw Materials and Pellets:

TGA and DTGA analysis was performed on PAN powder, KL, DMSO-2, and 60 wt % PAN/DMSO2 pellets. See Figures 1 A and IB. Weight loss in DMSO-2 began at ~50°C and completed at ~180°C, however, the weight loss related to DMSO-2 loss in the PAN/DMSO-2 pellets was dramatically delayed beyond ~180°C. The intermolecular forces between PAN and DMSO-2 could inhibit the loss of DMSO-2 from the fiber matrix beyond 180°C. To maintain a high degree of DMSO-2 retention during the compounding and bench scale processing, a maximum temperature of 180°C was used.

Bench Scale Spinning and Washing:

Bench scale melt spinning resulted in successful fiber formation of PAN/DMSO-2 AS and PAN-KL/DMSO-2 AS fibers as seen in Figure 2. The PAN/DMSO-2 AS fibers were used to determine the required washing time in 95°C water for DMSO-2 removal. The FTIR spectra for neat PAN/DMSO-2 fibers washed at different time intervals are shown in Figure 3. The peaks at 1283, 1130, 933, and 760 cm' ¹ were associated with the DMSO-2 components and decreased with washing in 95°C water up to 150 sec where DMSO-2- affiliated peak reduction ceased. Washing in 95°C water for 150 sec was chosen for pilot DMSO-2 removal.

Pilot Scale Compounding, Spinning and Washing:

Pilot scale melt-spinning was conducted at zone 1-4 temperatures being 150, 160, 170, 180°C, respectively, and spin pack temperature at 220°C. A spin pack temperature of 220°C was chosen to reduce the melt viscosity without exceeding the lower limit for commercially conducting stabilization reactions which could result in an unstable melt state. ^{10 13} The filaments were collected with 3 different AS take-up speeds: 40, 80, and 100 m/min. Each sample was then washed in 95°C water for 150 seconds. Figure 4A shows micrograph images of the cross-sections of neat and washed PAN fiber, while Figure 4B is a photographic image of exemplary fibers. Figures 5A and 5B show the effect of washing on linear density and cross-sectional area quantitatively. A decrease in macrovoids is seen with washing in 95°C water. The dissolution of the DMSO-2 present in the noncrystalline regions can provide for polymer chains to first swell in the presence of water, thus closing the macrovoids, then contract upon drying, resulting in the lower cross-sectional area as shown in Figure 5B.

The AS and washed XRD spectra for each speed are shown in Figures 6A and 6B. The ~17 and -30° peaks are associated with the hexagonal (100) and orthogonal (110) peaks in PAN, respectively. The additional peaks seen are associated with the DMSO-2 crystal lattice structures. Washing in 95°C water for 150 seconds eliminated the peaks associated with DMSO-2 leaving the hexagonal (100) and orthogonal (110) PAN peaks.

The mechanical properties as seen in Figures 7A-7D saw a distinct increase in tenacity and modulus, and a decrease in % strain at break with washing. The stress v strain graphs in Figure 8A show different behaviors between the neat and washed filaments. The neat filaments show a distinct yield point that is less pronounced among the washed filaments. This is evident by the SEM images of fiber fracture tips (see Figure 8B) post deformation in tension where the neat filaments see more pronounced microvoids - indicative of plastic deformation (i.e. crazing) as compared to the washed filaments, especially at the higher take-up speeds.

In summary, pilot scale 72-filament melt spinning of PAN was achieved through incorporating the melt-depressant agent dimethyl sulfone with as-spun take-up speeds up to 100 m/min. Washing in 95°C in water to remove dimethyl sulfone was shown to increase the tenacity and modulus of the as spun filaments without disrupting the PAN crystal structures formed during spinning.

REFERENCES

All references listed in the instant disclosure, including but not limited to all patents, patent applications and publications thereof, scientific journal articles, and database entries (including but not limited to UniProt, EMBL, and GENBANK® biosequence database entries and including all annotations available therein) are incorporated herein by reference in their entireties to the extent that they supplement, explain, provide a background for, and/or teach methodology, techniques, and/or compositions employed herein. The discussion of the references is intended merely to summarize the assertions made by their authors. No admission is made that any reference (or a portion of any reference) is relevant prior art. Applicant reserves the right to challenge the accuracy and pertinence of any cited reference.

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13. Gupta, A. K.; Paliwal, D. K.; Bajaj, P., Journal of Macromolecular Science, Part C 31, 1 1991. It will be understood that various details of the presently disclosed subject matter may be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.