Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains ix, 118 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 117-118).

No description available.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 222-230). Also available via the Internet.

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.

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

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.