Browsing by Author "Behnam Pourdeyhimi, Committee Co-Chair"

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Electrospinning Water Dispersible Polymers
(2008-05-13) Cannon, Kristin Marie; Don Shiffler, Committee Member; Behnam Pourdeyhimi, Committee Co-Chair; Samuel M. Hudson, Committee Co-Chair
Water-based electrospinning systems are important not only for environmental reasons, but also for toxicity reasons in biomedical applications such as drug delivery systems where residual solvent may be dangerous. However, very few polymers are water soluble. A method of electrospinning water dispersible polymers using a water soluble polymer as the template has been determined. The primary water dispersible polymer is a sulfonated co-polyester with an average 1.27 weight percent sulfur added to the backbone. Low percentages of an ionic species can be added to the polymer backbone to create water dispersibility without making the polymer water soluble. Such, polymers are known as ionomers and posses very unique behaviors. This work examines the solution behavior of this particular ionomer. Most of the characterization focuses upon the viscosity as a function of shear rate. Conductivity and surface tension are also examined. The results of experiments in electrospinning this co-PET with two different water soluble template polymers, poly(ethylene oxide) and poly(vinyl alcohol) is discussed as well.
Functional Textiles via Self-assembled Nanolayers and Atomic Layer Deposition
(2008-07-16) Hyde, Gary Kevin; Pamela Banks-Lee, Committee Member; William Oxenham, Committee Member; Gregory N. Parsons, Committee Co-Chair; Behnam Pourdeyhimi, Committee Co-Chair
An Investigation of Aerosol Filtration via Fibrous Filters
(2008-11-06) Wang, Qiqi; Behnam Pourdeyhimi, Committee Co-Chair; Hooman Vahedi Tafreshi, Committee Co-Chair; Timothy Clapp, Committee Member; Xiao-Biao Lin, Committee Member
The most common method of removing particles from a gas stream is via fibrous filters. However, most of the previous studies have been limited to systems consisting of rows of fibers (often in two-dimensional geometries) perpendicular to the flow direction. The current work is aiming to develop an understanding of the role of filter?s microstructure and manufacturing process. In the first part of this study, pressure drop and nanoparticle collection efficiency of lightweight spun-bonded media are simulated by solving the Navier-Stokes equations inside three-dimensional geometries resembling the microstructure of such media. These pressure drop and collection efficiencies showed a perfect agreement with experimental data. In the second part of this work, the influences of fiber length and compaction ratio of filter media on the pressure drop are discussed. Simulation data of staple fiber media have shown good agreement with Davies? empirical equation. Such an agreement indicates that, within the range of dimensions considered, the fiber length has no significant influence on the materials? through-plane permeability as long as the SVF remains constant. Our simulation results for nonwovens with different compaction ratios, together with our experimental data, indicate that pressure drop of the porous media increases with increasing the compaction ratio or temperature of the calender rolls. In the third part of this work, we presented our approach for modeling permeability of fibrous filters with bimodal fiber size distributions (referred to as bimodal filters in this context). The three-dimensional microstructures resembling bimodal filter media with random in-plane fiber orientation distribution were generated to compute their permeability constants. These results were compared with the previous analytical and numerical models as well as our experimental data. Here we concluded that there exists an area-weighted equivalent average diameter for each bimodal filter that can be used in the existing expressions for calculating the permeability of unimodal filters. The last part of this thesis is dedicated to studying the permeability woven fabrics. Concerned with the accuracy of the homogeneous anisotropic lumped model of Gebart (1992) for predicting the permeability of multifilament fabrics, we devised a series of numerical simulations conducted in full three-dimensional geometry of idealized multifilament woven fabrics wherein the filaments were packed in Hexagonal arrangements. While a relatively good agreement was obtained, our results indicate that Gebart?s model underestimates the permeability of multifilament fabrics at high yarn?s solid volume fractions. We also simulated the pressure drop of monofilament woven fabrics under tension where we observed a logarithmic relationship between the discharge coefficient and the Reynolds number of the flow.
Investigation of the utility of islands-in-the-sea bicomponent fiber technology in the spunbond process
(2007-10-02) Fedorova, Nataliya Vasylivna; Donald Shiffler, Committee Member; Stephen Michielsen, Committee Member; Trevor Little, Committee Co-Chair; Behnam Pourdeyhimi, Committee Co-Chair; Jan Genzer, Committee Member
Structure-Process-Property Relationships in Elastic Nonwovens Made From Multi-Block Elastomers
(2008-03-10) Begenir, Asli; Stephen Michielsen, Committee Co-Chair; Behnam Pourdeyhimi, Committee Co-Chair; Sam M. Hudson, Committee Member; Martin A. Hubbe, Committee Member
Melt-blown webs from ester and ether thermoplastic polyurethanes (TPU) and polyether-block-amide (PEBA) elastomers were produced at different die-to-collector distances (DCD) to study the correlation between polymer type, process conditions and web properties. Air temperature and velocity profiles were measured and modeled to correlate fiber formation to melt-blowing conditions. Isothermal crystallization kinetics was measured by DSC, and analyzed by traditional Avrami and model proposed by Kurajica. Web tensile properties were explained in terms of crystallization kinetics along with air temperature profile. Crystallization kinetic parameters derived from both models exhibited similar temperature, polymer type and hardness dependence. The air flow field from simulations showed good agreement with experimental profiles and enabled modeling of fiber formation in melt-blowing. Both air temperature and velocities dropped significantly even at the die tip and continued to fall rapidly until reaching a plateau. The crystallization onset temperatures were found to fall within DCD region of rapid air velocity and temperature drop. This suggests that polymers already started to crystallize before collector, the extent of which depends on crystallization kinetics. Web strength behavior was highly dependent on DCD and polymer hardness. By mapping crystallization behavior onto air temperature profile, polymer crystallization kinetics was observed to have a profound effect on web strength. This was clearly demonstrated in PEBA series, in particular with the hardest grade, P55 which produced the lowest web strength mainly due to its significantly higher crystallization rate. It is concluded that web tensile behavior is strongly dependent on degree of fiber solidification achieved within the web, which is determined by crystallization kinetics and distances traveled between die and collector. Moreover, polymer extrusion and air temperatures as well as air velocity are critical in determining the amount of time it takes for polymer melt to travel the distance from the die to collector and the temperature that fibers have upon reaching collector.