Thesis (M.S.)--University of Alabama at Birmingham, 2009. / Title from PDF t.p. (viewed June 30, 2010). Additional advisors: Derrick R. Dean, Selvum Pillay, Alan M. Shih. Includes bibliographical references (p. 80-83).

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1986. / Vita. Abstract. Includes bibliographical references (leaves 204-209). Also available via the Internet.

The material response of a graphite/polyphenylene sulfide (thermoplastic) composite system to a variety of loadings was experimentally investigated. Quasi-static tension tests were performed on specimens cut from unidirectional panels at angles of 0°, 90°, and 10° in order to the find material properties of the system. The moduli and strengths were compared to those of several other graphite/epoxy systems. The effect of molded-on end tabs on the strength and failure mode of 0° specimens was also assessed. Both quasi-static tension tests and cyclic tension-tension (R=0.1) fatigue tests were performed on (0/±45/90)_s and (0/90₃)_s specimens. A variety of NDT techniques were used to inspect the "as received" panels and to monitor the formation and growth of damage during quasi-static tension and cyclic fatigue testing. The "as received" panels were found to possess initial flaws that included warping of unidirectional panels, dense matrix cracking in all multi-directional laminates, and local matrix rich and matrix poor regions. The predominately observed damage mechanism occurring as a result of applied mechanical load was delamination. Comments on the ability of each NDT technique to locate and monitor damage occurring in each specimen type are also presented. A preliminary investigation of the creep response of ( ±45₂)_s specimens was performed. Seventy-two hour creep tests were performed at temperatures of 75°, 160°, 250°, and 350° Fahrenheit and at stress levels of 750 psi and 1000 psi. It was found that when testing specimens repeatedly, a strange stiffening phenomenon was observed to occur during the first creep test performed at 350°. After the initial creep test at 350° was performed, no further stiffening of the specimen occurred and all tests performed thereafter were found to be repeatable. The mechanism causing this stiffening phenomenon has not yet been determined, but such an effect is of obvious importance for design considerations and therefore warrants further study. / M.S.

Advanced thermoplastic composites are commonly manufactured from "'prepreg" materials, where the reinforcing fibers are preimpregnated with resin. The objectives of this investigation were to identify the critical parameters in impregnation of the fiber tow by a thermoplastic solution, and to produce high quality thermoplastic prepreg. Continuous carbon fibers (AS4 and AU4) were impregnated with a thermoplastic resin solution using a research scale, single tow, drum winding prepreg machine. The parameters varied to control the degree of impregnation of the fiber tow were, weight percent polymer in solution, die size, fiber tow tension, fiber tow velocity, and the use of impregnation pins. These parameters were varied during the prepregging operation and prepreg samples were evaluated to determine resin content. Viscosity studies were performed on the polymer solutions by means of a Rheometrics Mechanical Spectrometer. Thermogravimetric analyses were performed on the thermoplastic solution and the prepreg. Cross-sectional photomicrographs were obtained to determine the degree of impregnation and the fiber/resin distribution. Unidirectional laminates were fabricated from the prepreg. Transverse tensile and double cantilivered beam mechanical tests were performed. Fractography photomicrographs were taken. X-Ray photoelectron spectroscopy was used to investigate the possibility of residual solvent in the laminates. High quality prepreg was manufactured and the critical parameters in the prepregging process were identified and their effect on the prepreg was quantified. / Master of Science

Bisphenol-A based poly(arylene ether)ketones (PAEKs) are tough, amorphous processable thermoplastics possessing a glass transition temperature of approximately 160°C. In the form of a thermoset, these polymers have potential usages as structural engineering matrix resins or adhesives, as well as modifiers for existing engineering polymers. Thermosets of PAEKs can be prepared through the incorporation of amine, maleimide, or nadimide groups onto the ends of the polymer chains followed by the curing of the materials at elavated temperatures. Plates for mechanical testing, 1/8 inch in thickness or greater, were prepared by first degassing the polymeric powder under vacuum at temperatures 10-50°C above the Tg of the respective oligomer for short periods of time, followed by compression molding of the resulting material. The networks exhibited high fracture toughness values, as determined by 3 point bend measurements, Tg’s around 160 °C as well as a stable rubbery modulus to above 350°C, as determined by dynamic mechanical measurements. Toughness of these networks increased dramaticly with increasing Mc up to the chain entanglement molecular weight. Tg and rubbery modulus were only slightly altered by Mc. The swelling of these networks in chloroform reveals a two stage increase in solvent absorption. The two stages are believed to be related to the viscoelastic extension of the chains followed by subsequent disentanglement of dangling ends allowing further extension. The toughness behavior of thermoplastic PAEK oligomers versus molecular weight was found to parallel the oligomer’s melt viscosity behavior. As a modifier, PAEK cocured with bismaleimide produces network substantially tougher than the unmodified bismaleimide network. Control experiments with non-reactive PAEK oligomers demonstrated the necessity to functionalize the oligomers to produce the toughening effect. Cocured systems were found to possess a homogeneous morphology while physically blended systems phase separated. Swelling occurred in a single stage, possibly due to the high concentration of functional groups which eliminated dangling ends from the network. These networks possess a Tg at 160°C, associated with the relaxation of PAEK, and stable rubber modulus of above 350°C whose absolute value was a function of the BMI/PAEK ratio. / Ph. D.

The crystallization and melting behavior of copolymers (specially of those which partially exclude the and component) has not been well understood. Poly(ether ketone ketone) PEKK is such a partially excluding copolymer in which the crystalline phase tends to exclude one of two similar monads. Previous studies on PEKK have focused on effects of changing overall composition on the melting and crystallization behavior. These studies have demonstrated that PEKK tends to exclude one of two chemically similar monads from the crystalline phase, and the crystallization and melting behavior is affected as a result of this exclusion. However, the effect of changing linear chain architectures on the thermal behavior of such copolymers has not been investigated. In this study, the effect of changing architectures of the linear chain (blockiness) on the crystallization and melting behavior has been studied. The overall composition of the copolymer is maintained at 50% 2nd comonomer, and a series of samples prepared with different block lengths and amounts of branching. The crystallization and melting behavior of these samples is then studied using hot stage optical microscopy, scattering (small and wide angle X-ray scattering) and thermal analysis techniques (differential scanning calorimetry). It has been demonstrated that, upon changing from an alternating to a non-alternating structure, substantial amounts of 224 component are excluded from the crystalline phase and the melting temperature is raised considerably. Further, because of increased amounts of branching which accompanies the change in blockiness, the crystallization kinetics is slowed down. These results have been analyzed in terms of existing theories of copolymer crystallization, and some speculative arguments have been presented on the factors which affect the crystallization mechanism in such partially excluding copolymers. The validity of equilibrium thermodynamics based on the enthalpic approach has been analyzed. / Ph. D.

The synthesis and characterization of poly (arylene ether) s containing the phosphine oxide unit along the backbone were investigated and unique properties derived from the presence of this moiety were identified. The preparation of crucial phosphine oxide containing monomers which would be susceptible to the desired nucleophilic aromatic substitution polycondensation was achieved via Grignard routes. Thus, bis (4-fluorophenyl)phenyl phosphine oxide and bis (4-fluoropheny) methyl phosphine oxide were found to undergo successfully polymerization by a nucleophilic displacement reaction with aromatic bisphenols in the presence of potassium carbonate and dipolar aprotic solvents. The resulting poly (arylene ether phosphine oxide) s had glass transition temperatures ranging from 195 to 285°C depending on the rigidity of the bisphenol and the pendant group on the phosphorus containing monomers. Many properties were typical of their poly (arylene ether sulfone) and poly (arylene ether ketone) counterparts, including excellent hydrolytic, thermal and oxidative stability. Good dimensional stability and mechanical properties were also obtained. Physical blends and statistical copolymers, as well as polymers of controlled molecular weight and functionality, were also prepared via conventional techniques, yielding novel phosphorus containing compositions. Unique features of these poly (arylene ether phosphine oxide) s (PEPO) were discovered initially by thermogravimetric analysis in air. All PEPO gave significant amounts of phosphorus containing char at temperatures where other engineering polymers were completely volatilized. This behavior was related to the very improved self-extinguishing behavior of all the phosphorus containing systems. Unlike most phosphorus containing polyphosphonates described in the literature, the phosphorus-aryl carbon bond was hydrolytically stable. Additionally, these PEPO materials were much more resistant to aggressive oxygen plasma environments due solely to unique oxidized phosphorus surface layers formed upon exposure to these harsh conditions. Finally, metal complexation through the phosphine oxide unit was discovered to be a novel way to modify polymer properties. / Ph. D.

No description available.

No description available.

D. Tech. Polymer Technology. / Objectives of this work were to develop PLA/PBSA-based hybrid materials with better barrier properties, thermal stability, impact strength and at the same time, have relatively good strength and modulus. The specific objectives were: 1) To optimise PLA/PBSA blend composition for the desired blend properties. This entailed understanding of the role of specific interfacial area obtained from the morphologies of the blends in controlling the properties of the same and relate qualitatively, the phase morphologies to the properties of the PLA/PBSA blends. 2) To study the effect of annealing on the properties of PLA/PBSA blends. 3) To study the effect of organic modifiers on clay surfaces and the interlayer d-spacing of the clay on the morphology and properties of PLA/PBSA-clay composites 4) To study clay dispersion at various loadings and how it affects the crystallization of PLA and PBSA components in the blend.5) To study clay loading effect on the thermal and mechanical properties of the PLA/PBSA-clay composites. 6) To optimise the processing parameters, vis-a-vis: reaction time, coupling agent content, PLA/PBSA composition and processing sequence during in-situ reactive compatibilization of PLA/PBSA blends. 7) To improve the thermal stability and barrier properties through reactive processing of PLA/PBSA, in the presence of organoclays and a coupling agent. 8) To study the rheological properties of the blends prepared, as a function of clay content in the physically and reactively compatibilized PLA/PBSA blends.