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 bio-based products derived from agricultural products and byproducts. Agricultural Research Service (ARS) researchers in 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 and cotton fabric hand applications; (2) conversion of biomass to nanocrystals; (3) flame retardant cotton; (4) utilization of enabling technologies for improved flame retardant cotton; (5) and cotton-based blood clotting (hemostatic) and antibacterial dressings. Probable mechanism for flame retardant activity and durability related to Objective 1. Cotton contains naturally occurring chemicals that tend to confer flame retardant activity to nonwoven cotton fabrics. Research has shown how a naturally occurring polyphenol compounds from plants, tannic acid, acts with sodium ions to create a robust thermal barrier on cotton. Analysis of the rate of fabric burning revealed that the outer layer containing tannic acid decomposes in a two-step reaction, producing a distinctive protective barrier with post-burn surface features. Further analysis demonstrated that the presence of tannic acid in the cotton promotes the formation of the stable protective barrier that is sustained during the burning of the fabric. The thermal decomposition of the cotton fabric appears to be promoted by both the sodium-tannic acid component and an as yet unidentified component in the cotton fabric. A better understanding of the mechanisms of thermal decomposition will lead to better designs of flame retardant molecules and will enhance their thermal protective properties in apparel, mattress and furniture applications. Flame retardant cotton materials which relates to Objective 1. Treating cotton fabrics with multiple layers of intumescent nano-coatings, which are composed of phosphorus-nitrogen rich polymers, provides 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. 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. Analysis of the released gas products from ignition of the fabrics provided key data on the degradation of the treated fabrics during the burning process, which is useful to improve the design of the cotton fabrics. Moisture control, hygienic, and cotton fabric hand 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. A series of nonwoven blends composed of unbleached cotton, bleached cotton and minimal amounts of man-made fibers were designed and produced with the goal of understanding how a cotton-based diaper topsheet material functions in terms of both fabric hand, and its ability to manage urine uptake and storage. Cotton-based nonwoven fabrics that demonstrated better or comparable performance to a commercial topsheet were further examined for properties that promote a comfortable skin to fabric sensation. Thus, from a series of ten fabric blends it was found that a nonwoven fabric containing a high proportion of unbleached cotton with small amounts of bleached cotton and man-made fiber had improved softness, smoothness, flexibility, and formability. The results demonstrated that from a series of ten fabric blends a blend of 90/5/3/2 percent unbleached cotton/polypropylene/bleached cotton/ polyester fibers had improved properties of softness, smoothness, flexibility, and formability while promoting rapid passage of fluid to the diapers absorbent core. Thus, optimizing fiber blends in nonwoven cotton fabrics can impart efficient passage of liquid to the absorbent core of a diaper while imparting improved fabric hand associated with properties associated with comfortable fabrics. Cotton-based blood clotting (hemostatic) dressings with antimicrobial activity which relates to Objective 2. The development of robust hemostatic dressings that also have antimicrobial activity is required in pre-hospital medicine both in civilian and military trauma treatment improvements. Improvements in these are needed in the current day pre-hospital advanced wound care required for prolonged field care which raises new challenges with infection and tissue viability. Affordable and effective hemostatic and antimicrobial wound dressings are being developed for prolonged field care of open wounds to control bleeding and prevent infection. An antibacterial mechanism based on hydrogen peroxide generation that is produced directly from the cotton dressing fabric was developed from a simple treatment developed with unbleached cotton by applying small amounts of ascorbic acid (vitamin C). It was found that treatment of a cotton-containing dressing fabric with ascorbic acid affords antibacterial activity by inhibiting both gram negative and gram positive bacteria at 99.99 percent as measured in a standardized test used to assess antibacterial activity of textiles. Thus, an approach to treating the cotton-based hemostatic dressing with ascorbic acid was developed for potential commercialization based on standard textile pad-dry-cure, finishing chemistries. The antibacterial treatment is also being examined for its compatibility with a chemical treatment examined to promote hemorrhage control in cotton dressing prototypes. Blood clotting properties of treated fabric screened for hemorrhage control were tested using a blood clotting assay that measures both the time to formation of a clot and the onset of fibrin (the sealant that promotes and strengthens blood clots) formation. With regard to the actual hemorrhage control dressing prototype work formulations were developed to modify cotton dressings for accelerated control of arterial blood flow. The formulations were prepared based on the goal of achieving adherence of the active hemorrhage control agent to the cotton fabric to promote accelerated clotting. Fabrics that were modified with higher amounts of the hemorrhage control agent (greater than thirty percent by weight of fabric) typically demonstrated better activity and in some cases promoted completion of blood clotting in two-three minute time frames. The unbleached cotton is thought to work synergistically with the hemorrhage control agent to promote clotting. The unbleached cotton works synergistically with the hemorrhage control agent to promote clotting. Advanced spectroscopic and imaging techniques were used to determine the degree of fiber coating and the distribution of the hemorrhage control agent on the fabric surface by providing visualization of adherent nanoparticles at the cotton fiber level. Utilization of enabling technologies for improved flame retardant cotton related to Objective 3. The use of microwave reactors as a substitute for organic solvents is considered a green chemistry alternative. A microwave-assisted method that accelerates high add-on chemical treatments of cotton fabrics was discovered. The same microwave method was applied to the reaction of flame retardant compounds on cotton, and the net result of reacting these compounds on cotton by microwave assisted technology is improved flame retardant properties with the reduction of toxic smoke upon ignition of the flame retardant cotton. It is mainly useful to design and develop novel environmentally friendly small molecules and formulations that allow textiles of commerce to be flame resistant. We have developed an efficient method for the chemical treatment of a series of flame retardant compounds such as economical, commercially available inorganic compounds (urea and diammonium phosphate and phosphorus-nitrogen containing small molecules) on cotton fabrics. The final flame retardant results will provide useful fabric design criteria based on standard test methods. Conversion of two cotton biomass feedstocks 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. Cellulose nanocrystals were extracted from two agricultural by-products, cotton gin motes and cotton gin waste. A major challenge which was overcome was the analytical characterization of CNCs from the extraction processes. Several analytical methods were used on the cellulose nanocrystals to determine their size, shape, electrical charge, affinity to water and thermal properties. Using analytical characterization it was found that differences in the extraction method and chemical treatment resulted in differences in thermal properties and CNC stability in water. This work constitutes the necessary characterization of the physical properties of CNCs, which is an important first step, prior to blending CNCs as a reinforcing material to prepare useful plastic-like environmentally friendly materials, and applying it to cotton textiles for use in medical and hygiene applications.
1. Cotton-based blood clotting (hemostatic) dressings. 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 in armed forces soldier’s first aid kits. Cotton-based materials have been developed by ARS researchers in New Orleans, Louisiana, for applications in dressings that involve enhanced clotting rates. A nonwoven dressing prototype that principally contains unbleached cotton to enhance clotting and absorbance for bleeding control has been developed and commercialized. 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), two cotton-based dressings have been developed. One of the dressings was made commercially available in November 2018. The dressing is 33 percent lighter and 63 percent more absorbent than the standard crinkle-type cotton dressing made with bleached cotton. In addition to enhanced bleeding control properties it also resists adhering to damaged tissue and can be torn into small units for easy application. A second generation version of this product with 99.99 percent antibacterial activity against both gram negative and gram positive bacteria has also been developed by ARS scientists for prolonged field care. The antimicrobial, bleeding control gauze has a similar design and has been targeted for FDA approval and commercial manufacturing within the next year. The two cotton dressings also fulfill the requirement of a congressional mandate to use U.S. cotton in textile products utilized by the DoD. The potential impact of these types of cotton-based hemostatic dressings is to be found in improved dressings used by the Armed Forces and First Responders.
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