Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Typescript. Vita. Title from title screen of research.pdf file (viewed on March 6, 2009) Includes bibliographical references.

Fibrous filter materials are commonly adopted in a variety of industrial and domestic processes to remove fine particles. Filter performance may be assessed by two parameters: the proportion of particles passing through the media (penetration), and the resistance to gas flow through the filter (pressure drop). Another parameter, the filter lifetime, may be important where economical factors are key.

The use of natural fibers as reinforcement in thermoplastics presents an interesting alternative for the production of low cost and ecologically friendly composites. One of the advantages of using natural fibres is their low specific weight, resulting in higher specific strength and stiffness when compared to glass reinforced composites. Natural fibres also present safer handling and working conditions. They are non-abrasive to mixing and can contribute to significant cost reduction. This work is divided into two phases: Phase 1 deals with developing nonwoven mats composites from flax/polypropylene (PP) and evaluating their properties. Flax/polypropylene fibres (at different weight ratios) were processed by needle-punching technique in order to form nonwoven mats. The mats were compression-molded at a temperature of 180oC to form composite materials. The mechanical, thermal and viscoelastic properties of the composites were analyzed. Composites (untreated and silane-treated) were also subjected to varying conditions of temperature and humidity and the tensile properties of the conditioned and unconditioned composites were investigated. The mechanical properties (tensile, flexural and impact) of flax/PP composites were found to increase and reach maximum values at 30 per cent fibre loading and then decrease at higher fibre content. Thermal studies revealed that the composites were stable up to 320oC and samples containing 40 per cent flax fibres were found to exhibit greater thermal stability than neat PP. The dynamic mechanical analyses of the composites showed that the incorporation of flax in the composites resulted in an increase of the storage modulus with a maximum value exhibited by composite containing 40 per cent fibre loading. Composites containing chemically modified fibres exhibited low tensile modulus after conditioning. Phase 2 is based on the investigation of the effect of nano-calcium carbonate (CaCO3) on the properties of two types of polymer matrices: recycled PP and virgin PP. In this case, composites were prepared by melt-mixing and injection molding. The mechanical and thermal properties of the composites were characterized. The tensile modulus of the nano-CaCO3 filled PP (virgin and recycled) composites were found to increase and reach maximum at 30 per cent nano-CaCO3 loading, while the tensile strength decreased with increasing filler content. Thermal studies showed that the nano-CaCO3 filled PP samples exhibited a one-step degradation pattern and are thermally stable up to 450oC. The thermal stability of the samples was found to decrease following the addition of nano-CaCO3. SEM micrographs of the tensile fractured surfaces of composites of the nano-CaCO3 filled virgin and recycled PP revealed the presence of nano-CaCO3 agglomeration.

Tensile properties of polyethylene fibres are shown to be very good in comparison to properties of other advanced composite reinforcing fibres. Nevertheless, the use of polyethylene fibres in polymeric matrix composites suffers due to a poor fibre to resin adhesion. However, its ballistic properties are excellent because of the poor adhesion and also fibre ductility. Applications involving structural use of polyethylene fibres are limited by, among others, the low compressive and shear strengths. These are affected strongly by the degree of adhesion. Improvements in bonding are expected to result in greater commercial appeal for the fibres as the property limitations are reduced. Ultra Violet radiation has been shown previously, in laboratory scale batch studies, to induce graft co-polymerization of monomers to polyethylene films. Improvements in wettability and adhesion result when the grafted polymer is compatible to the bonding medium. In this study the technique was adapted to bench scale, continuous fibre treatment, whereby the monomer was surface grafted to the polyethylene substrate. Acrylic acid monomer was used for this due to its relative safety, small molecular size, and high reactivity. Reaction initiation was provided by use of a benzophenone photosensitizer due to the stability of polyethylene to UV radiation. The reaction was performed by pre-coating the fibres with reactants, then exposure to UV radiation. Results of the continuous process for fibre treatment indicate that the monomer concentration and temperature of the preliminary soakings are key variables. Adhesion improvement was measured by single fibre pullout tests and interlaminar shear strength (ILSS) tests. Of these, the ILSS appeared to be more sensitive for judging small improvements. Tensile tests were used to judge property deterioration due to treatment, and flexural property tests gave a preliminary indication of material behavior. The ILSS showed marked improvement from 1.5 ksi for untreated material to over 5.2 ksi for the better treatments. A competing treatment, plasma, shows ILSS values around 3 ksi. The flexural test indicated that failure of UV-grafted polyethylene was in tension, whereas failure of plasma and untreated material was in compression. The study has proven successful in improving the adhesion of polyethylene fibres to an epoxy resin matrix. Commercial viability is currently being developed through decreased process residence times and irradiation exposures. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Engineering therapeutic approaches to wound healing can be divided into two major categories of fibrous and non-fibrous approaches. There has been significant progress in designing artificial skin products to replace autografting. For patients with non-healing/hard-to-heal wounds, there is an unmet clinical need for inexpensive skin substitutes to be transplanted. In skin regeneration area of research, electrospinning is a very commonly used method of production of grafts for wound healing applications, owing its popularity to the fibrous nature of the resultant product, which mimics the extracellular matrix of the native skin. Despite the high degree of porosity in conventional electrospun scaffolds, the small pore size effectively limits the penetration of cells into the scaffold. Transplantation of such scaffolds with poor cell infiltration abilities may lead to a range of negative consequences, from prolongation of the first/destructive phase of inflammation to rejection of the scaffolds. Several experimental approaches have been developed to generate interfibrillar space in the electrospun scaffolds, including but not limited to modifications of the electrospinning set-up and inclusion of sacrificial components. It has been reported that scaffolds with larger pore diameters in the range of ~ 40-100 μm can modulate, moderate and reduce acute inflammatory responses of the body, by influencing macrophages biological behavior, and direct the course of the wound healing process to the tissue remodeling phase. Macrophages are the major cell component of innate immune system and play critical roles in clearance of pathogens, resolution of inflammation and wound healing following an injury. Macrophages are characterized by their diversity and plasticity. In response to environmental stimuli, they acquire different functional phenotypes of pro-inflammatory (M1) or anti-inflammatory (M2). In this thesis, we developed a novel unique gradient porous structure from a plant-based “green” soy protein isolate (SPI) with improved pore size for macrophages to infiltrate. We further showed the ability of the scaffold to modulate phenotype switch in macrophages in vitro and in vivo. The proposed scaffold, moreover, appeared to support transition of the inflammation process from the destructive to the constructive phase in vivo. Based on the promising results of this thesis, we propose our newly developed scaffold has the ability to be used as a new therapeutic modality for treatment of non-healing chronic wounds. / Bioengineering

Not available until OCRd / Master of Science

A new compact double-notched specimen for in-plane shear testing of isotropic, anisotropic and composite materials was developed. A preliminary test of the specimen was performed on a cross-ply laminate. High sensitivity moire interferometry was used to determine the shear and normal strains on the entire face of the specimen. The results of the test were compared to those of the Iosipescu specimen on the same material. The compact specimen produced a more uniform and more pure shear distribution than the Iosipescu specimen. Stiffness measurements of the composite material were made. A detailed investigation of the specimen was performed and it revealed important attributes and deficiencies of the specimen. Recommendations for future work are cited. The interlaminar shear response of a cross-ply composite was investigated. Shear strains on a ply-by-ply basis were measured using moire interferomety. Qualitative and quantitative information of the interlaminar shear characteristics of the material were obtained. The interlaminar shear modulus of individual plies and the effective modulus for the laminate were determined. Variations of nominally equal plies were observed. / Master of Science

The matrix-fiber stress transfer in glass/epoxy composite materials was studied using analytical and experimental methods. The mathematical model that was developed calculates the stress fields in the fiber, interphase, and neighboring matrix near a fiber break. This scheme takes into account the elastic-plastic behavior of both the matrix and the interphase, and it includes the treatment of stress concentration near the discontinuities of the fibers. The radius of the fibers and the mechanical properties of the matrix were varied in order to validate the mathematical model. The computed values for the lengths of debonding, plastic deformation, and elastic deformation in the matrix near the fiber tip were confirmed by measurements taken under polarized light on loaded and unloaded single fiber samples. The fiber-fiber interaction was studied experimentally using dog-bone samples that contained seven fibers forming an hexagonal pattern. / Master of Science

The effect of surface pretreatment on the physical and chemical properties of carbon fiber-polyimide matrix composite surfaces was evaluated. Eight pretreatments were studied: methanol wash, gritblast, sulfuric acid soak, ammonia plasma, argon plasma, argon plasma followed by ammonia plasma, nitrogen plasma, and oxygen plasma. The pretreated surfaces were chemically characterized through the use of XPS (X-ray photoelectron spectroscopy), ISS (ion scattering spectroscopy), and PAS-FTIR (photoacoustic Fourier transform infrared spectroscopy). Surface fluorocarbon contamination was appreciably reduced with gritblasting, argon plasma and oxygen plasma pretreatments. Specific functional groups were incorporated into the composite surfaces through the choice of gases used in the pretreatment. Physical changes were determined through the use of HR-SEM (high resolution scanning electron microscopy). With the exception of the macroroughening produced by gritblasting and the pitting produced by long exposure times in the oxygen plasma, no signlficant differences in the topography of the pretreated composites were observed. The wettability of the pretreated composite surfaces increased, as demonstrated with contact angle measurements, due to a combination of a decrease in the fluorocarbon contamination and an increase in the surface functionality present. / Ph. D.

The simulation program FWCURE [1] models the curing process and layer tension loss of axisymmetric filament wound composite cases during fabrication. For a specified temperature cure cycle, the model predicts the temperature distribution, resin degree of cure, viscosity, layer compaction, and fiber motion throughout the composite case during cure. The scope of the simulation program developed by Tzeng [1] has been extended, and the modifications to the FWCURE program are the goals of this investigation. Major modifications to FWCORE include a more general 2-D layer tension loss model, additions to an element curvature calculation routine, a new cure reaction kinetics model and viscosity model for a Fiberite-974 epoxy resin system, and modifications and additions to Input/Output (I/O) throughout the program. Modifications and additions to FWCORE are implemented in the analysis of an 18 inch diameter test bottle. Results of the simulation are compared with test data obtained during winding and cure of a graphite-epoxy 18 inch test bottle. Excellent agreement was obtained between the results of the model and data. Another major accomplishment involved coupling FWCURE with a thermo-mechanical stress simulation program called WACSAFE. When combined, the coupled program forms an improved comprehensive structural model which characterizes the thermal, chemical, physical, and mechanical processes occurring during winding and cure of filament wound composite cases. The complete simulation program should provide the process engineer with a resource to help select an optimum fabrication cycle, assess the processing characteristics of new matrix reein eystems, and act as a simulator to yield real time, closed loop process control. FWCURE should also provide information on the processing parameters that have the greatest effect on the final filament wound composite structure. / Master of Science