Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 135-142). Also available via the Internet.

Thesis (Ph. D.)--University of Washington, 1994. / Vita. Includes bibliographical references (leaves [297]-304).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 125-130). Also available via the Internet.

Thesis (M.S.)--Brigham Young University. Dept. of Technology, 2005. / Includes bibliographical references (p. 111).

Made available in DSpace on 2014-06-11T19:27:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-08-15Bitstream added on 2014-06-13T19:55:27Z : No. of bitstreams: 1 costa_ap_me_guara.pdf: 1665404 bytes, checksum: 7ed3e020368308910bf5f72563f3fd31 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A utilização de matrizes termoplásticas de elevado desempenho tem evoluído progressivamente como uma alternativa para aplicações aeronáuticas, dentre estas destaca-se o PPS (polisulfeto de fenileno). Durante sua vida útil, as aeronaves são expostas a uma grande variedade de condições ambientais que, associadas aos diversos tipos de carregamentos, encontram-se sujeitas a diversos tipos de tensões mecânicas. Dentre os processos disponíveis de união de peças a soldagem por resistência elétrica para compósitos vem sendo considerada, consistindo este processo na atuação de uma corrente elétrica entre as partes a serem unidas gerando o calor necessário para que ocorra a fusão da matriz. Desta forma, o objetivo deste trabalho é avaliar o efeito da temperatura, umidade e salinidade na resistência ao cisalhamento e no comportamento dinâmico mecânico do compósito PPS/fibras contínuas soldado pelo método de resistência elétrica. Com esta finalidade, placas de PPS reforçadas com camadas de tecidos de fibras de carbono e de vidro (compósito híbrido) foram soldadas pelo método de resistência elétrica. Os materiais, soldado e não soldado, foram caracterizados pelas técnicas de microscopia óptica, ultrassom, TGA (termogravimetria) e TMA (análise termomecânica). Após a realização desta caracterização inicial, os materiais soldados foram condicionados em ambiente higrotérmico, rico em névoa salina e em câmara de choque térmico e, posteriormente, foram ensaiados pelos métodos de cisalhamento ILSS e Iosipescu além de análise térmica por DMA (análise dinâmico-mecânica). De acordo com os resultados obtidos, todos os condicionamentos utilizados alteraram as propriedades de cisalhamento e temperatura de transição vítrea do material soldado / The thermoplastic matrixes applications are continually increasing as an alternative for aeronautical applications. Among them, the PPS (polyphenilene sulphate) presents a linear structure and high crystallinity (60-65%). During lifetime, airplanes are exposed to a large variety of environmental conditions, which, associated to many kinds of loadings, make them susceptible to many mechanical tensions. One of the junction processes, the resistance welding consists in the actuation of an electric current between the parts to be jointed, creating heat until the matrix starts to soften/merge. The objective of this work is to evaluate the effect of temperature, moisture and salinity on the shear mechanical and dynamic mechanical properties of the carbon fiber/PPS composite, welded with the electric resistance method. Therefore, hybrid carbon PPS plates were welded to glass PPS with the electric resistance method. The welded and non-welded materials were characterized by microscopy, ultra-sound, TGA and TMA. Then, the welded materials were conditioned in hygrothermal environment, saline fog and thermal shock. The conditioning samples are tested by the ILSS and Iosipescu shear method, and DMA thermal analysis. According to the results, the conditioning has altered the shear and vitreous transition properties of the welded materials

This project assessed fracture toughness (K[IC] and G[IC]) for thin-section injection-moulded PES and for which there are no standard fracture-mechanics tests. Standard methods of testing are based on thick specimens that are easily available for metals but unusual for injection mouldings. Tests were, therefore, made which adapted the standard Mode-I (crack-opening) tests to the thin sections of injection-moulded discs. Then the question of the tests' validity arose. Were the elastic assumptions being met? If both critical Mode-I stress-intensity factor and strain-energy release rate were found then a Young's modulus value could be derived. If this derived modulus when compared to the directly measured Young's modulus was found to be identical then the assumption of linear elasticity would be upheld. Two different styles of fracture-mechanics test were investigated: ones with explosive fracturing and one with controlled crack growth. In explosive fracture-mechanics tests, the fracturing of the testpiece was so rapid that the minimum data was collected, so many such tests had to be aggregated to sample the range of notch-depth possible. This was true for both the three-point-bend (TPB) and tensile tests made on single-edge-notched (SEN) bars cut from the discs. However, when the derived modulus for the explosive tests was compared with Young's modulus it was found to be smaller, so these tests did not uphold the assumptions of elasticity. The reason for this failure was found to be that the notch did not act like the sharp propagating crack required for successful tests. In the controlled crack-growth test sequence, a crack was grown across the diameter of an injection-moulded disc and measurements were made, as the crack progressed, of the crack's position, corresponding loading and work done. From this sequence of measurements, independent values of stress-intensity factor and strain-energy release rate, under quasistatic conditions, were calculated that produced values of derived modulus which were, at least, equal to the Young's modulus, thus upholding the elastic integrity of the test. Moreover, initial surges of crack-growth (similar to explosive fracturing) were shown by linear regression analysis to give larger stress-intensity factors and to be significantly different from the data collected only during controlled crack-growth. Thus, the use of controlled crack-growth is Justified as a more reliable method of fracture-mechanics testing. Yield stress measurements were also made and with the valid stress-intensity factor predicted plastic zone sizes entirely compatible with yielded regions observed as crazes whose lengths were reported by Hine.

The aim of this work was to synthesise poly(butyleneterephthalate) (PBT) poly(dimethylsiloxane) (PDMS) block copolymers, containing the hydrolytically stable Si-C linkage. A number of routes involving mutually reactive oligomers were studied. Once synthesised the effect of the copolymer as a toughening agent for the PBT matrix was investigated. Siloxane copolymer precursors were synthesised by an equilibration reaction. The relative molar mass (RMM) of the precursor was governed by the initial ratio of end blocker to cyclic species. The functionality of the precursor determined by the end blocker. alpha, to hydroxy PBT oligomeric precursors were chemically modified, if necessary, to form mutually reactive species. Initial block copolymer synthetic routes concentrated on chloroplatinic acid catalysed hydrosilations in solution. This involved alpha, to di (hydrosilane) PDMS and alpha, to divinyl functionalised PBT. The lack of a suitable common solvent together with competing side reactions limited the progress of this route. Melt hydrosilation reactions proved ineffective also, because of the thermal instability of the catalyst. Further block copolymer experiments involving mutually reactive oligomers were performed in the melt. The most promising of these was one of transesterification. This used alpha,o-hydroxypropyl PDMS (RMM 1000) and alpha,o-hydroxy PBT (RMM 2000) precursors. Analysis indicated successful reaction to form a copolymer of low RMM. A higher RMM copolymer was desirable, for improved mechanical properties, and a number of approaches to achieve this were followed. Problems of competing reactions and ineffective catalysis were encountered. However, a material with promising mechanical properties was formed when using a diisocyanate as a chain extender. A PBT-PDMS copolymer was blended by itself, and also together with high RMM PDMS, in the PBT matrix. The mechanical properties of the blends were studied and compared. An improvement in impact properties, as compared to PBT, was achieved when the copolymer was used as an emulsifying agent in a PBT-PDMS blend.

No description available.

Cellulosic thermoplastics are anticipated as promising replacements to petroleum-based thermoplastics, but their high manufacturing costs have limited wide-spread application. The primary objectives of this thesis were to use low-cost lignocellulose, practically forestry waste, as the raw material rather than more expensive purified cellulose in the preparation of new plastics and, consequently, to develop an economical reactive process focused on diminishing the use of expensive solvents in the thermoplasticization of lignocellulose. The thermoplasticization of lignocellulosic fibers started by developing a high solids content (60 wt%) twin-screw extrusion technique to defibrillate the raw material for the subsequent chemical modification. By this approach, the received lignocellulosic fibers showed improving handling as a feedstock for extrusion as well as chemical accessibility. To effectively wet the lignocellulosic fibers for chemical modification and avoid using expensive and largely ineffective solvents, a low-cost additive was derived by mimicking aspects of an ionic liquid using benzethonium chloride (hyamine) and sulfuric acid. The effectiveness of the hyamine/sulfuric acid wetting agent was demonstrated initially in a bench-top method where the additive also became chemically bonded to the lignocellulose and strongly contributed to its thermoplasticity. During acetylation, this new and low-cost wetting/functionalizing agent converted the lignocellulosic fibers into a compression-moldable thermoplastic. The molar ratio of benzethonium chloride to sulfuric acid was found to be the most significant variable to determine grafting behaviour as well as degradation of the polymer chains. Subsequently, this new modification chemistry was translated over to the environment of a twin-screw extruder to devise a continuous, greener method of thermoplasticization for lignocellulose. The new reactive extrusion process had a short reaction time of 45-90 s and yet showed a good tendency for producing a flowable thermoplastic suitable for melt molding without plasticizers. A notable benefit to the method was the moldable lignocellulosic bioplastic maintained the excellent stiffness inherent to cellulose. Moreover, by the reactive extrusion method, the properties of the lignocellulosic thermoplastics were found to be tunable with the selected esterifying agents (butyric anhydride versus acetyl anhydride) and the molar ratio of benzethonium chloride to sulfuric acid. A statistical analysis based on a Design of Experiment method revealed details on desirable extrusion conditions. The project concluded with improvements to the high solids-content process was exploring the novel concept of a recycle stream for reactive extrusion. The excessive esterifying agent content used in the initial studies was necessary to lubricate the fibrous mass inside the extruder else it would jam the process. This meant that the extrudate left the extruder with an unnecessary amount of reactant and required costly cleaning. The idea of recycling a portion of the newly made cellulosic thermoplastic was to add a natural lubricant and thereby lower the content of the esterifying agent in the extruder. Under optimal recycling conditions, a significant 50% decline in reactant was possible without decreasing the degree of modification or harming the thermoplasticity of the modified lignocellulose. / Thesis / Doctor of Philosophy (PhD) / Wood biomass is the most abundant renewable material on the planet and comprises polymer chains like plastics. These polymer chains in wood biomass are locked by strong bonds, which limits their mobility. It is for this reason that wood biomass can not “melt” like commercial plastics such as polyethylene, and thus limits its application in the manufacture of objects with complex shapes. Using chemical modifiers to react with the wood biomass can unlock those bonds among the chains and convert it into a “meltable” thermoplastic. The current preparation of thermoplastics from wood biomass is very costly because of using expensive purified cellulose and solvents to assist the reaction. This thesis describes the development of an economical reactive process for converting less purified wood biomass into thermoplastics. It used low-cost lignocellulose, practically forestry waste, and discovered a low-cost but effective reaction method for using less expensive reactants. Finally, a rapid mechanically assisted reaction process (called reactive extrusion) was adopted based on the new chemistry to convert the lignocellulose biomass with significantly fewer reactants than needed in a batch system.

Thermoset resin based fibre reinforced polymer-matrix composite materials (PMCs) have provided excellent solutions to many industries based on their great specific strength, high design freedom and other characteristics such as water resistance, corrosion resistance, tailorable electrical conductivity, tailorable thermal performance and many others. But, despite of all their benefits, the materials are also limited by uneconomical recycling and management post service life, demanding raw materials storage conditions, less than ideal environmental impact during manufacturing, and relatively low productivity. The purpose of the present work was to investigate economically feasible production of a continuous fibre reinforced thermoplastic composite (CFRTP) alternative solution, for an existing company, that could overcome weak points and limitations of thermosets under increasing environmental needs and pursuit of higher efficiency. Work aimed at fulfilling the following objectives: 1) document existing thermoplastic composite materials and understand selected manufacturing methods, raw materials, mechanical behaviour and operational feasibility; 2) select, design, and build a fully functional CFRTP manufacturing line; 3) design and run Taguchi methods to analyze the product using multifactorial ANOVA to gently introduce rigorous quality control; and 4) identify the input parameters that most affect output product quality, that could be used to optimize the process, as well as input parameters that have no statistically significant effects on the output and therefore do not warrant investment in funds and time in order to control them. Throughout the work, it was showed that CFRTP could been produced efficiently with consistent quality. Unidirectional prepreg can be used directly or further processed for usage in many industries such as pipelines, light construction and automotive components. The design of the CFRTP solution fulfilled necessary conditions and successfully produced CFRTP unidirectional prepreg product. Prepreg produced under 16 different sets of conditions was tested and data was collected. Using Taguchi methods, this study found that the fibre volume fraction, condition of impregnation mould, condition of cooling rollers and extruding temperature all have statistically significant effects on product quality. But limited by restriction from time and cost by production based environments, it is imperative to conduct this work perfectly, in later research a more focused study can be done based on the results of this study. Still, thesis demonstrates a CFRTP mass production solution, verifies CFRTP impregnation and offers a significant route for upgrading environmental protection and production efficiency. The work also identifies key parameters that affect unidirectional prepregs properties.