Natural Fiber Welding Research Articles

Evaluating the Effect of Applied Tension during Natural Fiber Welding of Lignocellulose Yarns

This study evaluated how applying tension in the axial dimension during Natural Fiber Welding (NFW) of lignocellulose yarn impacted the fibers mechanical and morphological properties. Understanding the combined effects of applied tension and polymer mobilization is vital both for controlling sample contraction during NFW experiments, and will inform the design of scale-up processes that rely upon tension for pulling yarn and cloth stocks through continuous treatment. The tensile strength and Young’s modulus of the fiber-welded taut linen yarns slightly increased over the tension values for the untreated linen. The greatest increase in the tensile strength and Young’s modulus of the treated linen yarn occurred when taut linen yarn was treated with either 1-ethyl-3-methylimidazolium acetate or acetonitrile at 40 °C for 60 s. No tensile value improvements were observed in the NFW treated taut bamboo yarns. However, slight increases in the energy at break and tensile strength were observed when bamboo yarn was treated with methanol or warm acetonitrile. It is thought that the observed tension property differences between the treated linen and bamboo yarns is related to the cellulose and lignin content in the tested material.

Integration of Functional Nanomaterials in Biopolymer Composites Using Ionic Liquid Based Methods

Ionic liquids (IL) have been shown to be effective solvents for the dissolution of a wide variety of natural polymers, and new materials can be created from these natural feedstocks by processes that involve their full dissolution and subsequent reconstitution. Yet, the dissolution and reconstitution processes eliminates the native polymer structure often resulting in materials with significantly degraded physical properties when compared to the native material. However, if only the surface layers of these natural materials are mobilized through an ionic liquid facilitated process called Natural Fiber Welding (NFW), the underlying material retains its native character and mechanical properties while still allowing for significant material modification. Furthermore, the addition of functional materials (e.g. magnetic, optical, conductive) into the IL welding solution, allows for these substances to be entrained in and on the surface of the substrate imparting unique properties to the natural materials. In this work metallic nanoparticles were synthesized in linen powders by the process of incipient wetness impregnation. The linen containing nanoparticles were added to an IL and then welded to the surface of a natural polymer substrate (e.g., cotton yarn) via NFW. The morphology of the welded materials and the distribution of nanoparticles was characterized with TEM, SEM, and fluorescent imagery. Raman and infrared spectroscopies were used to evaluate the impact of the nanomaterials on the spectroscopic properties of the biocomposites, and atomic force microscopy and tensile strength testing were used to evaluate the mechanical properties of prepared composites. Using a variety of magnetic measurement techniques, we explored how nanoparticle composition and structure relate to each systems observed magnetic properties, and how some show nanomagnetic behavior at low temperature. Overall, the prepared composites maintained many of the attractive properties of the native substrates, while still exhibiting the functional properties of the entrained materials.

Evaluating the Effect of Applied Tension during Natural Fiber Welding of Lignocellulose Yarns

This study evaluated how applying tension in the axial dimension during Natural Fiber Welding (NFW) of lignocellulose yarn impacted the mechanical and morphological properties. Understanding the combined effects of applied tension and polymer mobilization is vital for controlling sample contraction during NFW experiments, and it will inform the design of scale-up processes that rely upon tension for pulling yarn and cloth stocks through continuous treatment. The tensile strength and Young’s modulus of the fiber-welded taut linen yarns slightly increased over the tension values for the untreated linen. The greatest increase in the tensile strength and Young’s modulus of the treated linen yarn occurred when taut linen yarn was treated with either 1-ethyl-3-methylimidazolium acetate or acetonitrile at 40 °C for 60 s. No tensile value improvements were observed in the NFW treated taut bamboo yarns. However, slight increases in the energy at break and tensile strength were observed when bamboo yarn was treated with methanol or warm acetonitrile. It is thought that the observed tension property differences between the treated linen and bamboo yarns is related to the cellulose and lignin content in the tested material.

Sustainable and scalable natural fiber welded palladium-indium catalysts for nitrate reduction

In this work, we demonstrate the production of reactive, robust, sustainable catalysts for water treatment created through Natural Fiber Welding (NFW) of lignocellulose-supported palladium-indium (Pd-In) nanoparticles onto linen yarns. First, Pd-In catalysts were synthesized by incipient wetness onto ball-milled powders of linen. Our process preserved the lignocellulose, yielding small (5–10nm), near-spherical crystalline nanoparticles of Pd-In alloy and a uniform Pd-In metal composition throughout the fibers. Nitrate reduction tests identified the existence of an optimum Pd-In catalyst composition (5wt% Pd and 1.2wt% In with respect to lignocellulose) for maximum reactivity; the most reactive Pd-In catalyst was 10 times more reactive than the best performing Pd-Cu nanoparticles deposited on lignocellulose using the same approach. This improved performance was most likely due to more uniform distribution of alloyed Pd-In nanoparticles throughout the support. Nitrate reduction tests and X-ray photoelectron spectroscopy depth profiling of aged Pd-In catalysts showed that they remained stable and lost no reactivity during extended storage in air at room temperature. Next, the optimized Pd-In catalyst was fiber-welded onto linen yarns, using a custom-built yarn-coating system and a novel, scalable process that controlled catalyst loading, delivering a Pd-In catalyst coating onto the yarn surface. This fiber-welded Pd-In catalyst yarn was integrated into a novel water treatment reactor and evaluated during four months and more than 180h of nitrate reduction tests in ultrapure water. During this evaluation, the fiber-welded catalysts maintained their reactivity with negligible metal leaching. When tested in raw or (partially) treated drinking water and wastewater, the fiber-welded catalysts were robust and stable, and their performance was not significantly impacted by constituents in the complex waters (e.g. alkalinity, organic matter). Our research demonstrates an innovative, scalable approach through NFW to design and implement robust, sustainable lignocellulose-supported catalysts with enhanced reactivity capable of water purification in complex water chemistries.

Lignocellulose Fiber- and Welded Fiber- Supports for Palladium-Based Catalytic Hydrogenation: A Natural Fiber Welding Application for Water Treatment

In our study, lignocellulose yarns were fabricated via natural fiber welding (NFW) into a robust, free-standing, sustainable catalyst for water treatment. First, a series of powder catalysts were created by loading monometallic palladium (Pd) and bimetallic palladium–copper (Pd–Cu) nanoparticles onto ball-milled yarn powders via incipient wetness (IW) followed by a gentle reduction method in hydrogen gas that preserved the natural fiber while reducing the metal ions to their zerovalent state. Material characterization revealed Pd preferentially reduced near the surface whereas Cu distributed more uniformly throughout the supports. Although no chemical bonding interactions were observed between the metals and their supports, small (5–10 nm), near-spherical crystalline nanoparticles were produced, and a Pd–Cu alloy formed on the surface of the supports. Catalytic performance was evaluated for each Pd-only and Pd–Cu powder catalyst via nitrite and nitrate reduction tests, respectively. Next, the optimized Pd...

Preparation of Functionalized Yarns Via Ionic Liquid Based Natural Fiber Welding

Natural fiber welding (NFW) is a process that uses controlled amounts of ionic liquid and molecular co-solvent(s) to swell and mobilize portions of a natural polymer substrate. By carefully selecting factors controlling NFW such as time, temperature and solvent system composition, partial dissolution occurs, mobilizing and redistributing only a small portion of the natural polymer and leaving much of the underlying substrate intact. The NFW process results in fibers with a shell of dissolved/mobilized polymer, permanently adhered to both the outer diameter of the fiber and (depending on the extent of welding) to the surface of adjacent fibers. When polymeric and/or particulate materials are added during the NFW process, these substances can be integrated into the natural polymer matrix and modify its properties to include novel functionalities. In the present work we have applied the NFW process to the modification of natural polymer yarns. We have studied the processing conditions that impact the NFW of natural polymer yarns and the accompanied incorporation of functional materials (e.g., magnetic, conductive, and capacitive). We will discuss the preparation these functionalized yarns, and we will show data for their analysis using tensile testing, infrared spectroscopy, and scanning electron and con-focal fluorescence microscopies.

Natural Fiber Welding of Chitin and Chitosan on a Cotton Cloth Substrate: Novel Materials Displaying Antimicrobial Properties

Ionic liquids (ILs) can be used as solvents for biopolymers due to unique chemical and physical properties that enable mobilization and disruption of the hydrogen bonding present in the biopolymer structure. Chitin and chitosan are biopolymer known to have natural antimicrobial properties. The goal of this work is to functionalize a composite cotton yarn or cloth with a chitin or chitosan biopolymer, in order to exploit the bio-active properties of chitin or chitosan, while maintaining the intrinsic physical and chemical properties of cotton yarn. We will be using a method called Natural Fiber Welding (NFW) to incorporate chitin or chitosan biopolymers into cotton materials. Natural Fiber Welding is the process of full or partial dissolution of a substrate and the regeneration using ILs, such as 1-ethyl-3-methylimidazolium acetate. Using this process, chitin or chitosan is able to be permanently adhered and chemically bonded to the outer and inner surface of the native yarn. Changing factors, such as ionic liquid solution composition (introducing DMSO), temperature, time, and concentration of biopolymers alters the degree of biopolymer mobilization which influences what properties the composite yarn displays. In this study we will show results for chitin or chitosan welded into cotton composite materials. We will present data characterizing the physical, chemical, and biochemical properties of these composites. Data from confocal fluorescence microscopy (CFM), SEM imaging, and Bactericidal Killing Assays will be shown using E.Coli transfected with Green Fluorescent Protein. In conclusion, it appears that we can effectively coat and integrate chitin or chitosan onto the cotton material and the material exhibits antimicrobial properties.

Combining Mechanical Tension with Natural-Fiber-Welding Treatments of Cellulose Yarns

Natural-fiber welding (NFW) is an ionic-liquid based treatment method that partially dissolves a fibrous structure’s polymer chains to allow subsequent polymer-chain entanglement between adjacent fibers. NFW treatments can beneficially alter the tensile properties of treated fibrous structures through this polymer entanglement [1]. Up until now fibrous-structure samples were held in place during NFW treatments by applied force to ensure contact with heated platens or to prevent deformation and warping. This new study, however, purposefully applies force during the NFW treatments to evaluate the effect of applied force upon the resulting material properties of the treated fibrous structure. Understanding what additional effects tension has upon NFW treatments is vital to evaluating not just how to best control warping of experimental samples, but also how to design scaled-up NFW treatment processes that rely upon applied tension for pulling continuous feeds of yarn and cloth through equipment. To test the effect of mechanical forces during NFW treatment, tension was applied to natural fiber yarns in their axial dimension. The three main variables evaluated were (1) the magnitude of tensile force, (2) the time at which this tensile force began during the course of the NFW treatment, and (3) the NFW treatment parameters previously known to be vital like temperature, time duration, and ratio of 1-ethyl-3-methylimidazolium acetate to yarn. In this presentation we will present results of our investigations of these variables using tensile testing, infrared spectroscopy, con-focal fluorescence microscopy, and scanning electron microscopy. [1] L. M. Haverhals, W. M. Reichert, H. C. De Long and P. C. Trulove, "Natural Fiber Welding," Mcromolecular Materials and Engineering, 295, 425-430 (2010).

(Invited) Towards Advanced Functional Natural Polymer Materials through Ionic Liquid Based Methods

Throughout history humankind has exploited the remarkable properties of natural polymers such as silk and cellulose. In modern times, these natural materials still possess properties that rival the most advanced synthetic polymers. Recent work has shown ionic liquids (IL) to be effective solvents for the dissolution of a wide variety of natural polymers, and new materials can be created from these natural feedstocks by processes that involve their full dissolution and subsequent reconstitution. However, many reports show that the dissolution and reconstitution processes eliminate the native polymer structure, often with negative consequences to the physical properties of the resulting materials. Alternatively, if only the surface layers of these natural materials are mobilized through an ionic liquid facilitated process called Natural Fiber Welding (NFW), the underlying material retains its native character and mechanical properties while still allowing for significant material modification. Furthermore, the addition of functional materials (e.g. magnetic, conductive, antimicrobial) into the IL welding solution, allows for these substances to be entrained in and on the surface of the substrate imparting unique properties to the natural materials. Our group has endeavored to utilize NFW to modify natural materials to introduce novel functionalities. This work has encompassed the incorporation of a wide variety of polymeric, organic and inorganic materials into natural fiber matrices. Through the introduction of the appropriate materials we have been able to impart capacitive, conductive, catalytic, magnetic, optical, antimicrobial, and/or fire retardant functionalites into natural polymeric materials. In this presentation we will show our most recent efforts utilizing NFW to prepare novel functional natural materials.

Natural Fiber Welding of Chitin and Chitosan on a Cotton Cloth Substrate: Novel Materials Displaying Antimicrobial Properties

Chitin and chitosan are biopolymers known to have natural antimicrobial properties. The ionic liquid (IL) based process of Natural Fiber Welding (NFW) was used to integrate chitin and chitosan into and between the fiber surfaces of cotton cloth. The NFW coating process was evaluated using scanning electron microscopy. The antimicrobial properties of the NFW coated cloths was investigated using E.Coli transfected with Green Fluorescent Protein. Confocal fluorescence microscopy (CFM) showed that both chitin and chitosan coatings inhibited microbial growth with the level of the inhibition increasing with longer NFW.

Combining Mechanical Tension with Natural-Fiber-Welding Treatments of Cellulose Yarns

Understanding the combined effect of applied tension and polymer mobilization is vital both for controlling sample contraction during “natural-fiber welding” (NFW) experiments as well as for designing scaled-up NFW processes that rely upon tension for pulling yarn and cloth stocks through a continuous treatment apparatus. A preliminary set of tests evaluated the effect of applying tension in the axial dimension during NFW treatments of yarns. These tests with a ~0.4 mm diameter two-ply linen yarn show that when compared to untreated yarn, NFW combined with tension increases Young’s modulus by a factor of 1.68 while NFW alone increases Young’s modulus by a factor of 1.44. Any effects of either NFW combined with tension or NFW alone were not observed with a ~0.2 mm diameter three-ply mercerized cotton yarn.

(Invited) Natural Fiber Welded Composites: Electrodes and Capacitors

Natural fiber welding (NFW) is a method whereby solvent blends and process conditions are tailored to selectively swell and mobilize the biopolymers of fibrous, natural materials for functional (chemical and physical) modification.1-4 For example, careful control of solvent to substrate ratio, solvent composition (efficacy), as well as the time, temperature, pressure, and location of solvent exposure results in robust composites composed of fibrous substrates that are fused without glues or resins. The biopolymers within the cores of individual fibers may be demonstrated to retain their native structures and thus functionalities. In addition to unique fiber blends, other materials such as conductive carbons, magnets, fire retardants, et cetera may be incorporated during processing to yield highly functional composites that are sustainably produced and exhibit low embodied energy. In this presentation, we will discuss NFW processes to create flexible carbon-containing yarns for wearable supercapacitor applications. In particular, repeatable, scalable processes that generate composites that perform on par with similar state of the art devices reported in the literature. Given that these composites are based on truly ‘green’ cellulosic and lignocellulosic substrates (cotton and bamboo) and utilizing a nonfluorinated binder (cellulose from cotton), we believe this to be a significant breakthrough for the prospects of wearable energy storage.5-8 In addition, we will discuss the prospects for large scale nonwoven bio-based electrodes produced from inexpensive agricultural wastes and suitable for any number of important applications (e.g., filtration of pollutants from air and water). Acknowledgements: Portions of this work were funded by the Air Force Office of Scientific Research. Any opinions, findings, conclusions or recommendations expressed in the material are those of the authors and do not necessarily reflect the views of the U.S Navy or U.S Air Force. K. Jost acknowledges support from the DoD National Defense Science and Engineering Graduate (NDSEG) Fellowship.

Ionic Liquid Facilitated Generation of Functional Biopolymer Composite Materials

Ionic liquids (IL) have been the focus of materials research for some time due to their unique physical and chemical properties. Of significant interest is their ability to solubilize biopolymers such as cellulose, chitin, keratin, and silk. However, full dissolution and regeneration using IL solvents often results in biomaterials with inferior properties compared to the native material. When natural substrates are only partially dissolved and regenerated through a process called Natural Fiber Welding (NFW), much of the native biomaterial structure can be maintained while still opening up the outermost portion of fibers so that the physical and chemical properties may be manipulated and/or modified. Furthermore, if functional materials (e.g. magnetic, conductive, capacitive, antimicrobial) are present in the IL-welding solution, these materials may be entrained in and on the surface of the fiber substrate. In the present work we will discuss the spatially controlled application of the NFW process and how this can be used to generated novel conductive and capacitive structures.

Laser Induced Natural Fiber Welding of Cellulosic Substrates

Laser assisted heating of an ionic liquid (IL), 1-ethyl-3-methyl-imidazolium acetate (EMIAc), coated cotton paper substrate was used to effect natural fiber welding (NFW). By using a programmable commercial CO2 laser cutter with controllable parameters such as laser power and number of passes and tight control over IL solution composition and concentration (water content), spatially specific laser welding with a resolution of approximately 175 µm was achieved. Treated cotton papers were investigated through tensile testing, scanning electron microscopy (SEM), attenuated total reflectance infrared spectroscopy (ATR-IR), and confocal fluorescence microscopy (CFM).

Natural Fiber Welded Composite Yarns

In this work, all-natural textile composites were prepared from commercially available linen yarns and chitin. An ionic liquid (IL), 1-ethyl-3-methyl-imidazolium acetate, was used to dissolve chitin, a natural biopolymer found in the exoskeletons of crustaceans and insects. Chitin was incorporated into linen yarns via IL assisted natural fiber welding (NFW). These biocomposites have the advantage of maintaining the structural integrity of the underlying yarn while incorporating a functional biopolymer, chitin on the surface and within the structure. Composite materials were evaluated for chitin integration through tensile testing, scanning electron microscopy (SEM), and confocal fluorescence microscopy (CFM).

Ionic Liquid-Based Solvents for Natural Fiber Welding: Impact of Solvent System Composition

Certain ionic liquids (ILs) are known to be efficient solvents for biopolymers, in particular for cellulosic and silk based materials1. The ionic liquid solvent efficiency is strongly impacted by the presence of both impurities (e.g., water, residual reagents) and intentional additives (e.g., co-solvents or diluents)3,4. Natural fiber welding (NFW), the process of controlled partial dissolution and regeneration of biopolymers,5-7 is also affected by the presence of impurities and additives8. In this work we investigate the impact of impurities and additives on NFW. The extent of NFW was characterized by x-ray diffraction, ATR-IR, SEM, and mechanical property testing. These data are correlated with solvent physical properties, such as viscosity, density, and surface tension, as well as with solvent properties as indicated by their Kamlet-Taft parameters. For some of the systems investigated, there is a maximum solvent composition where polar aprotic solvents in conjunction with IL are more efficient at NFW than the IL alone. Surprisingly, this composition occurs when the mole ratio of IL to solvent is less than one to one. Understanding the factors that influence welding in these systems allows for greater control over the NFW process and facilitates the formation of functional biopolymer composite materials. References Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am Chem Soc, 2002, 124, 4974.Phillips, D. M.; Drummy, L. F.; Conrady, D. G.; Fox, D. M.; Naik, R. R.; Stone, M. O.; Trulove, P. C.; De Long, H. C.; Mantz, R. A. J Am Chem Soc., 2004, 126, 14350.Rinaldi, R. Chem. Commun., 2011, 47, 511.Mazza, M.; Catana, D. A.; Vaca-Garcia, C.; Cecutti, C. Cellulose, 2009, 16, 207.Haverhals, L. M.; Reichert, W. M.; De Long, H. C.; Trulove, P. C. Cellulose, 2010, 2985, 425.Haverhals, L. M.; Sulpizio, H. M.; Fayos, Z. A.; Trulove, M. A.; Reichert, W. M.; Foley, M. P.; De Long, H. C.; Trulove, P. C.Cellulose, 2012, 19, 13.Haverhals, L. M.; Nevin, L. M.; Foley, M. P.; Brown, E. K.; De Long, H. C.; Trulove, P. C. Chem.Commun., 2012, 48, 6417.Haverhals, L. M.; Brown, E. K.; Foley, M. P.; De Long, H.; Trulove P. ECS Trans, 2012, 50, 6

Laser Induced Natural Fiber Welding of Cellulosic Substrates

As excellent solvents for cellulose and silk, certain ionic liquids (ILs), such as 1-ethyl-3-methylimidazolium acetate (EMIAc),1,2 can be used for biopolymer modification and manipulation. Full dissolution and regeneration using IL solvents often results in biomaterials with inferior properties compared to the native material. When natural substrates are only partially dissolved and regenerated through a process we call Natural Fiber Welding (NFW), much of the native biomaterial structure can be maintained while still allowing for significant material modification. NFW enables the structural modification of the surface and incorporation of functional materials through the binding capability of the portion of dissolved biopolymer3-5. In the present work we have employed a laser as the heat source to initiate partial dissolution of a cellulose substrate causing NFW in a spatially-specific manner. By using a non-solvent for cellulose (e.g., water) with the ionic liquid as a means of inhibiting the dissolution process, heat becomes the controlling factor necessary to obtain significant biopolymer dissolution and mobilization. A CO2 laser was used to raster a specific pattern onto a cellulosic paper substrate coated with IL solution. Raster power, concentration of the ionic liquid and the number of laser passes affect the amount of heat absorbed into the biopolymer and the level of NFW. Through tensile testing, confocal microscopy, ATR-IR, and SEM imaging, the resulting modification of the biopolymers was characterized. References Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am Chem Soc, 2002, 124, 4974.Phillips, D. M.; Drummy, L. F.; Conrady, D. G.; Fox, D. M.; Naik, R. R.; Stone, M. O.; Trulove, P. C.; De Long, H. C.; Mantz, R. A. J Am Chem Soc., 2004, 126, 14350.Haverhals, L. M.; Reichert, W. M.; De Long, H. C.; Trulove, P. C. Cellulose, 2010, 2985, 425.Haverhals, L. M.; Sulpizio, H. M.; Fayos, Z. A.; Trulove, M. A.; Reichert, W. M.; Foley, M. P.; De Long, H. C.; Trulove, P. C.Cellulose, 2012, 19, 13.Haverhals, L. M.; Nevin, L. M.; Foley, M. P.; Brown, E. K.; De Long, H. C.; Trulove, P. C. Chem.Commun., 2012, 48, 6417.

Natural Fiber Welded Composite Yarns

In this application, an ionic liquid (IL), specifically 1-ethyl-3-methylmidazolium acetate (EMIAc), well known for its ability to dissolve a variety of biopolymers1-3, is used in conjunction with molecular co-solvents to prepare biopolymer composite yarns by a process we call natural fiber welding (NFW). NFW uses controlled amounts of IL and a molecular co-solvent to swell and mobilize portions of the biopolymer substrate. By carefully selecting factors controlling NFW such as time, temperature and solvent system composition, partial dissolution occurs, mobilizing and redistributing only a small portion of the natural fibers and leaving much of the underlying substrate intact.4-7 This results in fibers with a shell of dissolved polymer, permanently adhered and hydrogen bonded to both the outer diameter of the fiber and (depending on the extent of welding) to the surface of adjacent fibers. With the addition of a small amount of biopolymer into the IL solution, a NFW composite yarn can be created with the pre-dissolved biopolymer acting as an additional binder. Different combinations of biopolymer binder and substrate take advantage of the functional and structural benefits of both biopolymers. Binder can also be used to facilitate incorporation of functional materials (e.g., magnetic, electronic, photonic) into the yarn fiber matrix. References Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am Chem Soc, 2002, 124, 4974.Phillips, D. M.; Drummy, L. F.; Conrady, D. G.; Fox, D. M.; Naik, R. R.; Stone, M. O.; Trulove, P. C.; De Long, H. C.; Mantz, R. A. J Am Chem Soc., 2004, 126, 14350.Xie, H.; Zhang, S.; Li, S. Green Chem. , 2006, 8, 630.Haverhals, L. M.; Reichert, W. M.; De Long, H. C.; Trulove, P. C. Cellulose, 2010, 2985, 425.Haverhals, L. M.; Sulpizio, H. M.; Fayos, Z. A.; Trulove, M. A.; Reichert, W. M.; Foley, M. P.; De Long, H. C.; Trulove, P. C.Cellulose, 2012, 19, 13.Haverhals, L. M.; Nevin, L. M.; Foley, M. P.; Brown, E. K.; De Long, H. C.; Trulove, P. C. Chem.Commun., 2012, 48, 6417.Haverhals, L. M.; Brown, E. K.; Foley, M. P.; De Long, H.; Trulove P. ECS Trans, 2012, 50, 603.

(Invited) Knitted Electrochemical Capacitors Via Natural Fiber Welded Electrode Yarns

This report presents a novel ionic liquid-based method for fabricating flexible double layer supercapacitor electrodes utilizing natural substrates. It also investigates the performance of these yarns knitted as fabrics, and with other cellulose-based fibers welded with carbon particles. Scanning electron microscopy, mechanical properties testing, conductivity and other electrochemical testing are performed to characterize both individual yarns and knitted devices. Natural fiber welding (NFW) is a process that uses controlled amounts of ionic liquids (ILs) and molecular co-solvents to selectively swell and mobilize biopolymers in fibrous, natural materials for functional (chemical and physical) modification.1-4 NFW processes control and minimize the amount of dissolution to fibrous natural substrates. By carefully regulating the ratio of solvent to substrate, solvent efficacy, time, temperature, pressure, location of solvent exposure, etc., hydrogen bonding networks are reconfigured and extended by only mobilizing the outer shell of individual fibers. The result is that fibers are essentially ‘welded’ together while the cores maintain their native states. In this work, the fiber welding process has been modified to incorporate carbon materials into the biopolymer matrix, delivering flexible carbon containing yarns for wearable supercapacitor applications. To determine whether the material is a viable candidate for wearable supercapacitors, the welded carbon-yarns are coated with polymer electrolyte, twisted with stainless steel yarn (current collector) and electrochemically tested in a symmetric configuration through cyclic voltammetry, galvanostatic cycling, and impedance spectroscopy. Electrochemical testing performed on samples randomly selected across the entire length of yarn electrodes (typically 10-20 ft in length) yielded 8-12 mF/cm, comparable with previously reported literature. However, when the cotton is twisted with steel prior to coating, the capacitance dramatically increased to 45 mF/cm. Fabrication can have a dramatic effect on the electrochemical performance. Because mechanical properties of the cellulose yarns play a crucial role when knitting these capacitive yarns into full fabrics, tensile testing of the yarns pre- and post- welding was conducted. With each yarn, an improved strength was observed at the expense of elasticity; viscose and linen showed the most notable increases in strength (107%, 78% respectively) and toughness (both 22%). Though many of the cotton yarn electrodes showed favorable electrochemical performance, none were machine-knittable. The linen, viscose, and bamboo yarn supercapacitors were successfully machine knitted at Drexel’s Shima Seiki Haute Tech Lab. We currently attribute this to the length of the fibers playing a role in flexibility and mechanical strength within the yarn. More work is currently underway to explain this process, and fabricate a welded cotton yarn that can be knitted. To date, we have demonstrated a coating process that is repeatable and scalable (coating hundreds of feet at a time), inexpensive, and delivers competitive performance to similar reports in the literature. Given that composites are constructed from a truly ‘green’ substrate (cotton, bamboo, etc.) and utilizing a nonfluorinated binder (cellulose from cotton), we believe this to be a major breakthrough for the prospects of wearable energy storage.5-7 Acknowledgements: Portions of this work were funded by the Air Force Office of Scientific Research. Any opinions, findings, conclusions or recommendations expressed in the material are those of the authors and do not necessarily reflect the views of the U.S Navy or U.S Air Force. K. Jost acknowledges support from the DoD National Defense Science and Engineering Graduate (NDSEG) Fellowship.

Natural Fiber Welding: The Preparation of Cotton-Based Activated Carbon Electrodes

not Available.