Browsing by Author "Xiangwu Zhang, Committee Chair"

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Co-Presence of Durable Flame Retardant and Repellent Nano-Finishes.
(2010-05-13) Halbur, Jonathan; Xiangwu Zhang, Committee Chair; Jeffrey Joines, Committee Member; Henry Boyter, Committee Member; William Oxenham, Committee Member; Peter Hauser, Committee Member
Durable Flame Retardant and Antimicrobial Nano-Finishing
(2010-06-01) Dalton, Edward Arthur; Peter Hauser, Committee Member; Martin King, Committee Member; Xiangwu Zhang, Committee Chair; Henry Boyter, Jr., Committee Member
Due to the costs associated with processing, materials, and the inherent difficulties in applying durable flame retardant and/or antimicrobial finishes, alternatives to conventional finishing methodologies are one of the focal points in todayâ€™s textile research and industry. We, therefore, propose a new nano-finishing, involving the use of conventional flame retardants, titanium dioxide (TiO2) nanoparticles, and multifunctional silanes, to replace conventional methodologies as this new finishing combines the functionality of flame retardant and antimicrobial performance, each feeding off of the synergistic properties of the other. In this work, 100% cotton and 80/20 polyester/cotton fabrics were treated with a combination of Degussa P25 TiO2 nanoparticles, tetrakis(hydroxymethyl)phosphonium chloride and urea flame retardants, and silane cross-linkers (such as tetraethoxysilane). These fabrics were prepared using a conventional pad-dry-cure laboratory-scale methodology. Following the coating process, fabrics were evaluated for flame retardant performance through the use of a vertical flame chamber. Fabrics were also evaluated for antimicrobial performance under varying light conditions (i.e. ultraviolet, visible, and no light) at Aerobiology Labs in Dulles, VA. Fabrics showing most flame resistant promise were further investigated for finish durability by flame retardant testing following a series of 5 washing and drying cycles. These laundered fabrics received further flame retardant evaluation in the flame chamber and also ICP elemental analysis comparing active ingredient concentrations on the fabrics pre and post-laundering. Results of this work show that without the addition of TiO2, THPC and urea were unsuccessful in imparting flame retardant properties on 80/20 polyester/cotton blended fabrics. However, flame retardant properties of both 100% cotton fabrics and 80/20 polyester/cotton fabrics are enhanced as add-on of titanium dioxide nanoparticles increase, specifically when using the silane cross-linker tetraethoxysilane (TEOS). Properties that were enhanced include char length as well as length of ignition. As on-weight-of-bath percentage of TiO2 increased to levels of 6% and above, all poly/cotton fabrics self-extinguished. Similar results were observed on 100% cotton fabrics. This, in fact, does show that TiO2 possesses synergistic effects with the phosphorus-based, condensed phase flame retardant, THPC + urea. Flame retardant performance levels following the laundering process were much more variable. In the case of the 100% cotton fabrics, some flame retardant property enhancements were noted, however poly/cotton fabrics showed no improvement over the control. Antimicrobial properties of un-treated poly/cotton fabrics were compared to fabrics treated with only THPC + Urea flame retardants and a combination of THPC + Urea + TiO2. Un-treated poly/cotton fabrics had no resistance to bacteria as each sample exhibited colony growth after 24 hours of incubation. THPC proved to be antimicrobially active against gram positive S. aureus under no light and active against gram negative K. pneumoniae under no light, visible light, and UV light. THPC + Urea + TiO2 proved to be antimicrobially active against both gram positive S. aureus and gram negative K. pneumoniae under no light, visible light, and UV light. This shows that both THPC + Urea and THPC + Urea + TiO2 have antimicrobial efficacy, however, the efficacy of THPC + Urea + TiO2 has higher overall efficacy than THPC + Urea as it is able to effectively eliminate both S. aureus and K. pneumoniae at all conditions. It is suggested that in future works, further attempts are needed to increase durability of flame retardant and antimicrobial coatings to the abrasive forces of laundering. Other cross-linkers, flame retardants, and application methodologies should be investigated.
Lithium Alloy-Carbon Composite Nanofibers for Energy Storage by Electrospinning and Carbonization
(2009-10-30) Ji, Liwen; Peter S. Fedkiw, Committee Co-Chair; Saad A. Khan, Committee Member; Russell E. Gorga, Committee Member; Xiangwu Zhang, Committee Chair
Nonwovens Containing Novel Polymer Fillers.
(2010-06-14) Jung, Kyung Hye; Behnam Pourdeyhimi, Committee Chair; Xiangwu Zhang, Committee Chair; Saad Khan, Committee Member; Samuel Hudson, Committee Member
Platinum and Platinum Alloy-Carbon Nanofiber Composites for Use as Electrodes in Direct Methanol Fuel Cells
(2010-04-20) Lin, Zhan; Xiangwu Zhang, Committee Chair; Wendy E. Krause, Committee Co-Chair; Saad A. Khan, Committee Member; Samuel M. Hudson, Committee Member
In response to the energy needs of modern society and emerging ecological concerns, the pursuit of novel, low-cost, and environmentally friendly energy conversion and storage systems has raised significant interest. Among various energy conversion and storage systems, fuel cells have become a primary research focus since they convert chemical energy directly into electrical energy with high efficiency and low pollutant emissions. For example, direct methanol fuel cells (DMFCs), which supply the electrical energy by converting methanol to energy, are an ideal fuel cell system for applications in electric vehicles and electronic portable devices due to their relatively quick start-up, rapid response to catalyst loading, and low operating temperature. However, the wide commercial use of DMFCs in advanced hybrid electric vehicles and electronic portable devices is hampered by their high cost, poor durability, and relatively low energy and power densities. In order to address these problems, their research focuses on the development of highly active electrode catalysts coupled with a suitable electrode structure for the oxidation of methanol at the anode and the reduction of oxygen at the cathode to attain high efficiency of DMFCs, and subsequently lowering the cost. In this dissertation, the fabrication of novel platinum and platinum alloy nanoparticle-loaded carbon nanofibers (CNFs) for use as electrodes in DMFCs is demonstrated through electrospinning, carbonization, and deposition. The resulting CNF-based electrodes possess the properties of high electroactive surface area, good catalytic abilities towards the oxidation of methanol and the reduction of oxygen, and great long-time stability. As a result, DMFCs using these CNFs-supported platinum and platinum alloy nanoparticles as electrodes offer many advantages, such as improved electrocatalytic abilities, long-term stability, easy fabrication, low cost, and environmental benignity. Therefore, this new technology opens up new opportunities to develop high-performance electrode materials in the future for high-performance DMFCs, which are one of the promising power sources for consumer devices and electric vehicles, and play a critical role in solving the worldwide critical energy issue.