Browsing by Author "Xiangwu Zhang, Committee Member"

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    Degradation Studies of Polypropylene Fibers and Nonwovens with Prodegradant additives
    (2010-04-28) Viswanath, Vidya; Richard Kotek, Committee Chair; Xiangwu Zhang, Committee Member; Peter hauser, Committee Member
    The purpose of this research is to investigate an inexpensive pro-oxidant and pro-degradant additive system that can be applied during melt processing to produce biodegradable polyolefin-based (PP) nonwovens. The first phase of this research dealt with polypropylene filaments with pro-degradant additives. PP filaments with TDPAâ„¢ and ECM MasterBatch Pelletsâ„¢ additives were spun and characterized for their physical and chemical properties after xenon arc lamp exposure. Tensile studies showed significant loss of elongation and tenacity in additive containing samples on xenon arc lamp exposure. IR studies confirmed the formation of carbonyl compounds marked by an increase in carbonyl and hydroxyl index thereby indicating the occurrence of photooxidation of polypropylene. The second phase of the research involved the production of spunbond polypropylene nonwovens with TDPAâ„¢ and ECM MasterBatch Pelletsâ„¢ additives. These nonwovens were subjected to 3 types of degradation i. e. abiotic conditions of xenon arc lamp exposure and biotic conditions of vermicomposting and soil burial and subsequently characterized for their physical and chemical properties. Xenon arc lamp exposed nonwovens showed a drastic reduction in tensile strength (peak load) as compared to vermicomposted and soil buried samples. IR studies confirmed the occurrence of bio-chemical degradation having occurred in soil buried samples. It can be inferred that degradation of polypropylene filaments and nonwovens with additives depends on various factors like the additive type (TDPAâ„¢ or ECM MasterBatch Pelletsâ„¢) or the amount of the additive used, type and nature of degradation carried out (abiotic or biotic).
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    Develop a More Biodegradable/Biocompatible Hemostatic Fabric for Treatment of Bleeding Wounds
    (2009-07-20) Ina, Maria; Elizabeth G. Loboa, Committee Member; Samuel M. Hudson, Committee Chair; Wendy E. Krause, Committee Co-Chair; Xiangwu Zhang, Committee Member
    Hemostatic wound dressings help control traumatic external bleeding by enhancing or accelerating the natural clotting process through various physical reactions. Since the fatal traumatic hemorrhage remains one of the most challenging problems for both military and civilian medicine, efficient hemostatic wound dressings have been in high demand. Currently, several hemostatic dressings have been commercially available for acute hemorrhage, however, they still have some limitations in terms of cytotoxicity, biodegradability, sterilization, and cost performance. Thus, the development of effective biocompatible hemostatic dressings that overcome these limitations has been needed. The goal of this study is to investigate the potential application of Bombyx mori silk fibroin fibers as hemostatic wound dressings. First, the silk fibers were treated with two kinds of neutral salt [calcium nitrate tetra-hydrate (Ca(NO3)2 4H2O) and calcium chloride (CaCl2) ] / alcohol [methanol and ethanol] systems in order to decrystallize theirβ-sheet crystalline structure and improve the water absorbability and biodegradability. The decrystallization was carried out by controlling the solvent concentration and environment temperature. FTIR and X-ray demonstrated that most effective decrystallization of silk fibers were performed with the treatment in 50% (w/w) Ca(NO3)2 4H2O/methanol at 65℃, accompanying obvious decrease in the crystal size. Next, the blood clotting ability of the treated silk fibers was investigated by blood coagulation test. Even though any evident blood clot formation on the silk fibers was not confirmed during the test, the blood was separated into two phases and erythrocyte sedimentation was observed at different rate for each specimen. The silk fibers treated with most severe condition caused slower erythrocyte sedimentation compared with the non-treated silk fibers, suggesting less blood coagulation ability. Previously it has been reported that surface of silk fibroin fibers is hydrophobic and blood proteins interact with the silk fibroin through strong hydrophobic interaction. The obtained results suggest us that the decrease in hydrophobicity of the silk fibers surface due to decrystallization resulted in less interaction with blood proteins. Based on this result, we modified the silk fibers with sodium dodecyl sulfate (SDS) to give hydrophobic portion on the silk fiber surface. The difference in blood coagulation behavior between SDS-modified fibers and non-modified fibers was compared.
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    Mechanical and physical properties of electrospun nanofibers
    (2009-08-13) Zhang, Shu; Xiangwu Zhang, Committee Member; Russell Gorga, Committee Member; Alan Tonelli, Committee Member; Wendy Krause, Committee Chair
    The process of electrospinning was utilized to fabricate randomly aigned nylon6 nanofibers and aligned nylon6 nanofibers. Polymer concentration affecting electrospinning was investigated. This parameter was evaluated using degree of crystallinity by differential scanning calorimetry (DSC) as well as visual images produced by scanning electron microscopy (SEM). DSC data demonstrated that more crystals were formed with lower polymer concentrations; SEM images revealed that slimmer fibers were produced by lower concentrations. The mechanical properties of unoriented fibers and aligned fibers were tested on Instron 5544. The result of tensile tests indicated higher Young’s modulus and tensile strength of aligned nanofibers than that of unaligned fibers. The SEM images at broken edges of fibers illustrated different broken mechanisms of these two forms of nanofibers. The broken mechanism of aligned nanofibers was further confirmed by crystallinity parameters obtained from DSC and fiber diameter shown from SEM images.
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    Nanolayer Self-assembly on Ionic Fibers
    (2009-06-19) Wang, Zhengjia; Orlando Rojas , Committee Member; Peter Hauser, Committee Chair; Stephen Michielsen, Committee Member; Xiangwu Zhang, Committee Member
    The application of electrostatic self-assembly techniques in textiles has been explored. The layer-by-layer and atomic layer deposition have been used as new methods of textile modification. The use of layer-by-layer and atomic layer deposition offer the possibility of achieving fully conformal, uniform functionalization of textile fibers of any shape. The optimum processing conditions that allow the selective and controlled deposition of organic, inorganic, and metallic substances on textile substrates via self-assembled nanolayers and atomic layer deposition techniques have also been investigated. However, non-uniform surface and irregular shapes in yarns and fibers, especially the natural fibers increase the difficulties of these applications. Recent studies stated the feasibility of using electrostatic self-assembly on cationic cotton substrates. The goal of this research was to determine the charge density on ionic cotton fibers, which directly affect the electrostatic self-assembly. The ionic cotton fabric was produced after treatment of the substrate with a salt of chloroacetic acid or 3-chloro-2-hydroxypropyltrimethyl ammonium chloride. This research also provides a better understanding of layer-by-layer adsorption behaviors of positively or negatively charged polymer solutions on ionic cellulose films as measured by quartz microgravimetry. At neutral solution pH the adsorption of polyelectrolytes on ultrathin cellulose films was found to depend mainly on the charge density of the adsorbing macromolecule and that of the substrates. At the same adsorption condition, the thickness and surface excess (surface concentration) of the adsorbed species are controlled by the nature of the substrate and polyelectrolyte solution.
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    Novel Cellulose Solvent System and Dry Jet Wet Spinning of Cellulose/ED/KSCN Solutions
    (2008-04-07) Lee, Hyun Jik; Martin W. King, Committee Co-Chair; Richard Kotek, Committee Chair; Xiangwu Zhang, Committee Member
    The ethylenediamine/potassium thiocyanate salt (ED⁄KSCN) system was found to be a novel solvent system for the dissolution of cellulose. The solubility of KSCN in ED, the dissolution of cellulose, proper coagulants and coagulation rate of cellulose⁄ED⁄KSCN solution, dry jet wet spinning process of cellulose⁄ED⁄KSCN (7⁄65⁄35, w⁄w) solution and physical properties of cellulose fibers via the ED⁄KSCN solvent system were investigated. The maximum solubility of KSCN in ED was 44 wt% at room temperature and the ED⁄KSCN solvent had the best dissolving power on cellulose in ratio of ED⁄KSCN 65/35 (w⁄w). The dissolution of cellulose took place at a high temperature (60-70 °C), and the maximum solubility was achieved 12 wt% for cellulose of DP 450 in the ED⁄KSCN 65⁄35 (w⁄w). Several different coagulants were tested for coagulation study and methanol was found to be a proper coagulant for our solvent system. Coagulation rate of methanol in the cellulose/ED⁄KSCN (7⁄65⁄35) solution was also calculated as 3.75 x 10-1 mm⁄min1⁄2. Cellulose fibers via the ED⁄KSCN solvent system were successfully produced by the dry jet wet spinning system. Cellulose fibers showed excellent mechanical properties compared to commercialized cellulose fibers such as Lyocell and rayon fibers. In our spinning system, spin draw ratio affected the mechanical properties of fibers the most. As the spin draw ratio increased, the fiber tenacity and fiber modulus tended to increase gradually, but fiber elongation decreased. For the morphology of cellulose fibers via the ED⁄KSCN solvent system, the fiber showed a round shape and a relatively compact structure, and micro-fibrils were not observed.