1a. Objectives (from AD-416):
1. Enable, from a technological standpoint, new commercial processes for the production of cotton-based products with enhanced flame retardant and moisture control properties. 2. Enable new commercial processes for manufacturing cotton-based body-contacting materials for use in biomedical, biosensor and hygienic applications. 3. Enable new commercial processes involving supercritical fluids, microwaves, ultrasound, or ionic liquids for the production of cotton-based products.
1b. Approach (from AD-416):
The U.S. cotton industry continues to face supply and demand concerns. Since cotton is used in manufactured products, the industry has been challenged by the downsizing of manufacturing facilities that traditionally provide a major underpinning to domestic cotton consumption. Thus, with the goal of giving U.S. cotton utilization a competitive edge, research emphasis will be placed in cotton fiber science and product development where consumer and industrial needs are unmet and show promise. Some of the areas of consumer need for cotton products and process potential are flame retardant durable goods and apparel, and nonwoven body-contacting materials including improved wound dressings and hygienic/incontinence nonwovens, advanced nonmaterial’s. Enabling technologies that will enhance the likelihood of success and keep pace with industrial innovations include enzymatic bioprocessing, microwave-assisted synthesis and nanotechnology. To accomplish this, a three part approach will be taken: 1) Synthesizing FR compounds will include cross-linking small molecules, binding agents and reactive electrophilic functionalities. The treated fabrics will be tested using standard FR tests and the pyrolysis mechanism and gas emissions will be assessed to develop robust FR treatments for potential commercialization. 2) A broad set of characteristics implies a varied approach to design and preparation of cotton-based prototypes as body-contacting materials. Hemostatic and chronic wound dressings, incontinence absorbents, associated top sheet(s), and contiguous acquisition and absorbent layers of these materials constitute one general group, and nanocellulosic protease biosensors still another. Structure activity relations in turn rely on structural analysis including electrokinetic parameters (fiber surface chemistry),fluorescence, colorimetry, infrared spectroscopy, x-ray crystallography, and computational chemistry to list some of the primary and pivotal technologies to enable structure activity relations. 3) Four technological processes (supercritical carbon dioxide fluid, microwave radiation, ultrasonic energy, and ionic liquids) will be collectively explored as avenues of research, leading to the development of value-added products derived from cotton cellulosic sources. This multifaceted technological approach will ensure that leads are generated in the form of novel synthetic flame retardant (FR) compounds, nonmaterial’s, extruded bioorganic fibers, moisture control fabrics, ethanolic biofuel, and bio-finished cotton fabrics.
3. Progress Report:
Progress was made on all three objectives, all of which fall under National Program 306, Component 2, Quality and Utilization of Agricultural Products, Non-Food. Progress on this project focuses on Problem 2A to increase or protect the market demand for (or increase the value of) existing U.S.-produced non-food biobioased products derived from agricultural products and byproducts. Agricultural Research Service (ARS) Cotton Chemistry Utilization researchers at Southern Regional Research Center (SRRC), New Orleans, Louisiana, have developed new products, applications, and processes for expansion of domestic cotton in the areas of: (1) moisture control properties and hygienic applications; (2) conversion of biomass to nanocrystals; (3) flame retardant cotton; (4) utilization of enabling technologies for improved flame retardant cotton; (5) cotton-based blood clotting (hemostatic) dressings; and (6) chronic wound dressing materials. Moisture control properties and hygienic applications related to Objectives 1 and 2. The nature of liquid absorbency in both baby and adult diapers and its effect on comfort is not well understood. The domestic consumption of cotton could be increased if applied to the comfort and performance efficiency of diapers. ARS researchers have investigated these problems on different cotton blends composed of cellulose and man-made materials which possess a wide range of water absorbency and sensory properties. The absorbent properties of blended fibers were examined using sophisticated technologies and standardized test methods. A series of nonwoven blends composed of unbleached cotton, and blended with polypropylene, polyester, and bleached cotton fibers were designed and produced with the goal of understanding how a cotton-based diaper topsheet material functions in terms of fabric hand, and its ability to manage urine uptake and storage. Thus, the blends were examined for surface properties that influence performance properties that effect the efficiency of the diaper and demonstrated better or comparable performance to a commercial topsheet. To understand properties that influence the whiteness of the material, the material strength, capacity, and performance efficiency of the diaper were examined. Based on a collaboration with a nonwovens engineering specialist, fabric hand was measured as a function of sponginess, crispness, smoothness, stiffness and flexibility. The results show there is an optimal blend of fibers, which imparts ideal passage of liquid to the absorbent core, whiteness and comfort properties. Conversion of a cotton biomass feedstock to nanocrystals related to Objective 3. When cotton is treated with an acid it forms very small crystals called cellulose nanocrystals (CNC). CNCs are small, yet, pound for pound they are stronger than steel and have applications ranging from construction, biomedical, energy, electronic, and wastewater treatment. However, a major challenge is the yield of CNCs from the process. A common biomass feedstock for conversion to CNCs is pine wood sawdust with a yield of 18.7%. ARS researchers showed that CNCs can be produced from cotton gin waste in 21.8% yield and from cotton gin motes in 35.4% yield, which is 16.6% and 89.3% higher, respectively, than the pine wood sawdust yield. This means that cotton gin waste and cotton gin motes are excellent feedstocks for CNC production. Analysis has also shown that the size of the CNCs produced using cotton gin motes are ideally suited for applications in which material strength is important. Flame retardant cotton materials which relates to Objective 1. Flame retardant coatings that swell to protect a fabric by sealing gaps of exposure during a fire are referred to as intumescent. Treating cotton fabrics with intumescent nano-coatings, composed of phosphorus-nitrogen rich polymers and prepared via by assembling multiple layers the cotton fabric provided good flame retardant properties. The LbL (layer-by-layer) method was initiated with a flame retardant formulation containing casein, nano-clay and inorganic compounds as key constituents. LbL assemblies designed for flame retardant properties were prepared by a traditional textile finishing process (pad-dry-cure method) with coating formulas consisting 10-40 bilayers. By treating the cotton fabric with coatings, composed of phosphorus-nitrogen rich polymers the layer-by-layer assembly conferred anti-flammable properties to the cotton material as judged by three independent flame retardant tests. All of the LbL fabrics passed tests which demonstrated the flame retardant efficacy of the materials. Utilization of enabling technologies for improved flame retardant cotton related to Objective 3. An innovative approach for preparation of flame retardant cotton fabric was obtained by conducting the process in pressurized chamber filled with carbon dioxide, termed supercritical carbon dioxide (scCO2). A novel phosphorus-nitrogen compound was designed and synthesized with flame retardant properties, and the chemical structure characterized spectroscopically. Cotton fabrics were treated with the flame retardant compound using scCO2 as a solvent vehicle for the chemical reaction. Flame retardant activity of the resulting cotton fabrics was characterized with three standard tests for validation. The resulting flame retardant cotton fabrics were imaged microscopically at the fiber level. The images of the cotton fiber demonstrated that the scCO2 approach to preparing the flame retardant cotton provides a coating of the cotton fibers which is thought to prevent the fabric from being burned completely. Thus, the use of scCO2 enables the coating of cotton fibers as a ‘wrapping layer’ to protect the cotton fabric at a fiber level from being destroyed by heat and flame. It was determined through thermal analysis of the fabric’s reaction to fire that the mechanism of flame retardant activity may also be attributed to a sulfur-phosphorus bond in the structure of the cotton fiber coating. This is currently being tested. In a similar manner a promising method for promoting rapidly prepared and high add-on flame retardant cotton fabrics with chemical treatments was discovered using microwave-assisted technology. The combination of phosphorus and nitrogen offers several advantages to flame retardant safety considerations including char formation from phosphorous, incombustible gas without toxic smoke from nitrogen, and above all, the synergistic property from both enhancing the ability to retard flame propagation. Cotton-based blood clotting (hemostatic) dressings which relates to Objective 2. Mitigation of battlefield injury and hemorrhage is the highest priority of U.S. military trauma surgeons and researchers, and hemorrhage control is an important first-line measure of treatment by medics or emergency medicine personnel. In a collaborative effort with a stakeholder, the industrial development of cotton-based nonwoven materials designed to accelerate blood clotting was initiated. The preparation and testing of nonwovens containing unbleached cotton, bleached cotton, and polypropylene fiber blends was established at a set ratio to determine the effect of varying nonwovens process pressures and fabric densities on the materials ability to enhance clotting performance. Determination of the blood clotting activity of the materials was based principally on blood clotting analysis methods developed for fiber-based materials and absorption capacity to determine the relative roles of blood coagulation factors, blood platelets, and materials response to blood. Based on these results a lead candidate for commercialization was selected, and the blend ratio modified based on the production specifications of the stakeholder’s industrial nonwovens producer. In collaboration with a stakeholder, a commercial prototype was produced in high volume, and a sterilization trial performed. The resulting sterilized cotton-based dressing was confirmed for positive hemostatic activity, and the stakeholder has scheduled commercial production. Chronic wound dressings related to Objective 2. In recent years design features of dressings have addressed science that enables and accelerates wound healing in chronic wounds. Hydrogen peroxide has both antimicrobial and enhanced cell proliferation activity beneficial to wound healing. ARS researchers have recently determined that unbleached cotton can generate low levels of H2O2 associated with a therapeutic influence on chronic wound healing. In a study to ascertain how unbleached cotton can be supplemented to develop and modulate levels of hydrogen peroxide production, a series of copper/ascorbate formulations were developed on cotton. Formulations were identified for optimal hydrogen peroxide generation by preparing a library of copper/ascorbate ratios and assaying for hydrogen peroxide levels. Copper/ascorbate formulations were prepared on one hundred percent nonwoven greige cotton. Two types of cotton-grafted formulation were prepared wherein one was adsorbed on the fiber, and the other attached by way of in situ copper nanoparticle formation. Formation of a copper nanoparticle complex with the cotton resulted in a formulation that would not leach out in water. Subsequent findings reported from collaborative labs on the cotton-copper-ascorbate formulations revealed that both an antimicrobial effect on pathogenic bacteria and compatibility with fibroblast growth necessary for wound healing can be realized by adjusting the copper/ascorbate formulation ratios. Thus, developing an improved understanding of how wound dressings may be designed to address critical unsolved issues in wound repair and treatment is an impetus for the development of safe, economical, and highly functional materials for patients.
1. Moisture control applications for hygienic and wearable fabrics. ARS scientists in New Orleans, Louisiana, developed new cotton fabrics for diapers and incontinence products. Incontinence topsheet materials which are largely polypropylene are a 50 million ton per annum market. Cotton’s share in the growing incontinence product market has made more than a foray by beginning to penetrate specialty green applications that utilize organic motifs to market highly functional cotton-based incontinence products in the U.S., Europe, and Asia. The use of hydroentangled unbleached, greige cotton fibers in topsheet materials are at the center of a growing market for their use in the diaper or incontinence products. Greige cotton fibers are naturally soft to the touch, water repellant, and slightly yellow in color due to trace amounts of pectin’s and waxes. If not for the yellow appearance, these fibers would be acceptable in many consumer products. In a research project, the off-white greige cotton fibers were blended with small quantities of blue polyester fiber, which offset the yellow appearance by making the greige cotton appear whiter. Additionally, the blended blue fiber affected the water repellant and softness properties of the greige cotton. The research project was expanded to include bleached cotton and polypropylene fibers. Several nonwoven fabrics were produced from a blend of four different fibers, each with unique comfort, whiteness and moisture handling properties. Cotton-based incontinence products may be improved based on unbleached nonwoven cotton blends that have previously been shown to possess highly favorable properties including softness and key performance functions as low rewet, rapid strikethrough, and high volume fluid acquisition to prevent leakage. These findings should improve the use of cotton-based topsheets in incontinence products and the corresponding topsheet market.
2. Innovative technologies to convert cotton gin waste and cotton gin motes to cellulose nanocrystals. ARS scientists in New Orleans, Louisiana, developed new high value materials from cotton gin waste. Harvested cotton is processed into cleaned cotton fibers though a process termed ginning. Utilization of cotton gin waste by-products that are low fiber quality and result from this process, represent an unsolved problem. A process to convert the gin waste by-products to a high value form of cellulose (cellulose nanocrystals, CNC) has been discovered. Cellulose nanocrystals (CNC) are in the early stages of many industrial applications which range from automotive to medical to consumer packaging. Market trends indicate a rapid increase in demand for CNC from $18 million in 2014 to over $116 million in 2019. This, combined with cotton gin wastes and cotton gin motes’ low commercial value, make these materials an excellent feedstock for cellulose nanocrystal production. Using a highly acidic process method, we have produced cellulose nanocrystals from cotton gin waste and cotton gin motes in higher yields than is currently obtained from other commercially-available biomass feedstock such as pine wood sawdust. Analysis has shown that CNCs made from cotton gin motes are uniform in size which is important for certain applications that require strong materials. These results will greatly expand the use of low-value cotton gin by-products in high-value, consumer-driven applications and meet industrial stakeholder demand for cost effective sources of cellulose for increased nanocrystal production.
3. Flame retardant cotton with environmental friendly design developed for flammable materials related to Objective #1. ARS scientists in New Orleans, Louisiana, developed new types of flame retardant cotton. Layer-by-Layer (LbL) is a fabrication technique used to deposit alternating layers of oppositely charged minerals. LbL has high potential as a flame retardant. The use of layer-by-layer to prepare flame retardant cotton fabrics is a simple approach to incorporate various flame retardant molecules including clay particles onto cotton fabrics. These clay treatments also provide significantly different physical and chemical properties to cotton that may be advantageous to moisture management, strength, and absorptivity. By treating fabrics with flame retardant coating, composed of phosphorous-nitrogen rich polymers and prepared via layer-by-layer assembly, the cotton fabric can be rendered anti-flammable. These materials are designed to be permanently attached to the cotton so as to not wash off during laundering. There is little doubt that if fire retardant treatments can be made safer and more durable, the market for cotton will increase greatly. The layer-by-layer self-assembly process would provide an excellent thermal protection for medical, military, and large scale emergency uses where a low cost, short term product is desired.
4. Supercritical carbon dioxide technology to enable efficient preparation of flame retardant textiles related to Objective 3. ARS scientists in New Orleans, Louisiana, developed a method for efficient preparation of flame retardant fabrics. Petroleum-based approaches to large scale chemistries used to make flame retardant materials for consumer use are being re-directed to green chemistry, and more efficient green chemistry approaches to cotton chemistry utilization are desirable to impart flame retardant character to cotton. Due to its environmentally benign character, supercritical carbon dioxide (scCO2) is considered green chemistry, and thus is seen as a potential substitute for petroleum-based organic solvents utilized in chemical reactions. Fabrics treated with a compound that confer flame retardant activity were neither consumed by flame, nor produced glowing embers upon self-extinguishing. Furthermore, microscopy demonstrated that the flame retardant mode of action may reside in how the scCO2 promotes coating of the fabrics surface based on the surface morphology of char areas of treated and untreated fabrics. This approach could provide a rapid, simple, approach to uniformly coating cotton fibers with an effective flame retardant. Thus, it would be of benefit to commercial producers who have large scale scCO2 to produce flame retardant materials industrially.
5. Microwave-assisted technology to enable accelerated and efficient preparation of flame retardant textiles related to Objective 3. ARS scientists in New Orleans, Louisiana, developed a method for efficient preparation of flame retardant fabrics. A microwave-assisted one pot chemical treatment initiated with a minimum amount of solvent is a more efficient technique in contrast to traditional chemical treatment on textiles to impart flame retardant activity. The new protocol has the advantages of shorter reaction time, a simple procedure and an environment friendly green concept. The new microwave-assisted method will be of interest and use to professionals engaged in new materials designing in textile industries to create new marketable uses such as firefighter apparel, institutional draperies and upholstery, carpet, transportation blankets and seat covers, children’s sleepwear, and bedding etc.
6. Cotton-based blood clotting (hemostatic) dressings related to Objective 2. Excessive bleeding from traumatic wounds is the leading cause of death on the battlefield, and the second leading cause of death in the civilian trauma setting. Thus, materials that promote rapid blood clotting has relevance to both patient survival and optimal recovery. Cotton dressings have historically been carried by armed forces soldier’s first aid kit. Cotton-based materials have been developed by ARS scientists in New Orleans, Louisiana, for applications that involve enhanced clotting rates. In a joint development project among ARS scientists, cotton farmers, commercial nonwoven fiber and fabric distributors, and a company that supplies the Department of Defense (DoD), a cotton-based dressing has been developed, and scheduled for commercialization third quarter of 2018. The dressing also fulfills the requirement of a congressional mandate to use U.S. cotton in textile products utilized by the DoD. The potential impact of these type of cotton-based hemostatic dressings is to be found in improved dressings used by the Armed Forces and First Responders.
7. Chronic wound dressing and antimicrobial materials to enable wound healing related to Objective 2. ARS scientists in New Orleans, Louisiana, developed materials to promote wound healing in chronic wounds. Development of antimicrobial and wound healing dressings is important to both improving and sustaining cotton’s role in wound care products and healthcare materials. In previous work ARS researchers characterized the role of copper and ascorbic acid supplemented to unbleached cotton to produce therapeutic levels of hydrogen peroxide that would stimulate wound healing. A new procedure to affix copper to materials using ascorbic acid was developed as a green alternative. This approach to treating unbleached cotton with nontoxic agents is useful both to prevent leaching of the reagents from the material, and as a source of hydrogen peroxide, an antimicrobial compound, that is generated at therapeutic levels for as much as two days. A finding demonstrating the relative contribution of molecular components inherent to the unbleached cotton fiber supplemented with non-toxic, inexpensive small molecules suggests that both antimicrobial and wound healing materials can be prepared from inexpensive unbleached cotton nonwovens. The impact of the work may be realized in supplying a highly functional economical alternative for wound healing and antimicrobial materials, and will have applications to affordable highly functional, mechanism based chronic wound dressings and healthcare barrier material applications such as operating scrubs, drapes, pads and sheets.
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