This work has been concerned with the dimensional stability and the structure-property relationships of thermoplastics reinforced with particulate and fiber fillers. The first part of this study was concerned with ascertaining the main causes of warpage observed for injection-molded thermoplastics reinforced with high aspect ratio fibers. Typically, warpage in injection-molded fiber reinforced thermoplastics is primarily attributed to residual thermal stresses associated with shrinkage and thermal contraction of the parts. Therefore, it is assumed that flow-induced stresses generated during mold filling do not play a significant role in the warpage. The warpage of PP composites reinforced with TLCP fibers was found to increase with an increase in fiber loading. The shrinkage and the thermal expansion of the TLCP/PP composites and, hence, the thermally induced stresses decreased with an increase in fiber loading while the flow-induced stresses increased. The increase in the flow-induced stresses was attributed to an inhibition of stress relaxation and greater generation of orientation of the polymer chains with an increase in fiber loading. Therefore, it was found that in order to accurately predict the warpage of fiber reinforced thermoplastics, the flow-induced residual stresses must be accounted for. The second part of this work was concerned with minimizing the particle loading of reinforced PC/PBT composites while maintaining the stiffness, i.e. modulus, and the dimensional stability of injection molded flat panels. This was accomplished by using high aspect ratio (≈100-150) nano-clays as opposed to micron-size talc (≈5-10). It was found that by using nano-clays surface modified with a quaternary ammonium salt that contained two hydroxyl groups as opposed to fine talc particles, the level of particle reinforcement could be reduced from 6 to 1 wt% without sacrificing the modulus of the reinforced PC/PBT composites. Further benefits included a 26% increase in flexural strength, 77% increase in the tensile toughness and 3% reduction in the density of the reinforced PC/PBT composites. An increase in the modulus and tensile toughness was observed even though there was evidence of loss in molecular weight of the PC/PBT matrix, which was supported by the rheological behavior of the composites. / Ph. D.

Photopolymerization is a growing field within the realms of polymer and material science. With diverse applications, ranging from coatings and adhesives to newer technologies such as 3D printing photopolymerization continues to increase its prevalence and influence. This research examines fundamental structure property relationships between large prepolymer structures within a formulation and the resulting impact on thermo-mechanical properties in photocurable resins. Most prepolymer molecules utilize a “one pot” synthesis with little to no control over the placement of photoreactive moieties such as epoxies and (meth) acrylates. We have utilized novel prepolymer molecules synthesized using controlled radical polymerization to allow direct control over the placement of reactive groups. The ability to control the location of reactive groups in prepolymer molecules can also lead to the formation of multiple domains within the resulting photocured thermoset. This separation is achieved by concentrating the reactive groups at specific locations in the prepolymer backbone, e.g. at the end or near the center of the prepolymer molecule. The nonreactive groups may form one domain within the thermoset network while the reactive portion of the prepolymer forms a second phase with reactive diluent molecules. Additionally, various architectures allow greater control over polymer network formation and crosslink density. Through these manipulations of macromolecular architecture, we have been able to manipulate various thermo-mechanical properties. Using various architectured prepolymer, we have been able to generate materials with multiple glass transitions while also increasing the rate of reaction and total conversion as compared to randomly functionalized control formulations.

A new but relatively simple processing study was conducted to investigate the microstructure-property relationships of alumina/aluminium titanate (AAT) composites. The objectives of this study were: (a) to develop a process for fabricating AAT and β-spodumene modified AAT composites using a solid-state reaction method and functionally-graded AAT using an infiltration technique, and (b) to evaluate the effects of dispersed aluminium titanate (AT) on the phase relations, microstructure and mechanical properties of alumina-based composites. The study has revealed that the processing procedures played an important rule in the microstructural development of AAT composites. The microstructure and properties of AAT composites have been found to be strongly influenced by the presence of dispersed AT. The phase relations in the AAT system have been characterised by x-ray diffraction (XRD) and neutron diffraction (ND). Rietveld analysis showed that the AT content increased in proportion with the amount of rutile added. The dynamic ND study showed that AT commenced to form at ~1310°C The presence of AT caused a reduction of hardness but an improvement in fracture toughness. In addition, the presence of AT hindered the processes or kinetics of sintering and densification. The use of β-spodumene has been investigated as a liquid-phase-sintering aid for the densification of AAT composites. XRD, ND, differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Vickers indentation were used to characterise the effect of β-spodumene on the phase relations, densification, microstructure and mechanical properties of AAT composites. The presence of β-spodumene was found to have a profound influence on the phase relations, densification, microstructure and properties of AAT composites. / The addition of β-spodumene caused a small reduction of AT content and a commensurate increase of alumina phase. Functionally-graded AAT composites have been successfully synthesised through infiltration of porous alumina preform with a solution containing TiCl4. The infiltration kinetics of liquid into porous alumina preform has also been investigated and modelled. It was found that the infiltration rate equation proposed by Washburn was proven to be suitable for describing the kinetics of infiltration in terms of preform sintering temperature, viscosity, and multiple infiltrations. The influence of applied pressure was consistent with the model proposed by Travitzky and Shlayen, where the applied pressure enhanced the rate of infiltration. Pre-sintering of alumina preform at 900, 1000 and 1100°C for 2 h resulted in different rates of infiltration which may be attributed to a varying degree in tortuosity of the pore channels. The graded composition character of functionally-graded AAT composites has been determined by XRD and grazing incidence synchrotron diffraction (GISRD). Graded compositions from Rietveld refinement analysis showed that the concentration of AT decreased with depth. In contrast, the α-A12O3 content increased with depth. Microstructural examination by SEM showed that the content of AT grains was the most abundant near the surface and decreased gradually with an increase in depth. The hardness results showed that FGM had a soft graded-region (AT rich) but hard non-graded alumina region. / The lower hardness in the graded region can be attributed to the presence of intrinsically soft AT phase. The presence of graded AT caused a considerable improvement in damage tolerance. The isothermal decomposition of AT at 1100°C both in air and vacuum has been studied. Both ex-situ and in-situ studies have been conducted to examine the effect of environment on the decomposition behaviour of AT. The addition of MgO was effective in enhancing the thermal stability of AT against decomposition both in air and in vacuum.

This research is focused on investigating the effect of carbon nanotubes on macroscale composite laminate properties, such as, interlaminar shear strength, interlaminar fracture toughness and electrical conductivity along with studying the micro and nano-scale interactions of carbon nanotubes with epoxy matrix via thermomechanical and electrical characterization of nanocomposites. First an introduction to the typical advanced composite laminates and multifunctional nanocomposites is provided followed by a literature review and a summary of recent status on the processing and the characterization work on nanocomposites and composite laminates. Experimental approach is presented for the development of processing techniques and appropriate characterization methods for carbon nanotubes reinforced epoxy resin based multi-functional nanocomposites and carbon fiber reinforced polymer composite laminates modified with carbon nanotubes. The proposed work section is divided into three sub-sections to describe the processing and the characterization of carbon nanotube reinforced epoxy matrix nanocomposites, woven-carbon fabric epoxy matrix composite laminates modified with selective placement of nanotubes and unidirectional carbon fiber epoxy matrix composite laminates modified with carbon nanotubes. Efforts are focused on comparing the effects of functionalized and unfunctionalized carbon nanotubes on the advanced composite laminates. Covalently functionalized carbon nanotubes are used for improved dispersion and fiber-matrix bonding characteristics and compared with unfunctionalized or pristine carbon nanotubes. The processing of woven carbon fabric reinforced epoxy matrix composite laminates is performed using a vacuum assisted resin transfer molding process with selective placement of carbon nanotubes using a spraying method. The uni-directional carbon fiber epoxy matrix pre-preg composites are processed using a hot press technique along with the spraying method for placement of nanotubes. These macroscale laminates are tested using short beam shear and double cantilever beam experiments for investigating the effect of nanotubes on the interlaminar shear stress and the interlaminar fracture toughness. Fractography is performed using optical microscopy and scanning electron microscopy to investigate the structure-property relationship. The micro and nano-scale interactions of carbon nanotubes and epoxy matrix are studied through the processing of unfunctionalized and functionalized single wall carbon nanotube reinforced epoxy matrix nanocomposites. The multifunctional nature of such nanocomposites is investigated through thermo-mechanical and electrical characterizations.

No description available.

Providing sustainable supplies of water and energy is a critical global challenge. Polymer membranes dominate desalination and could be crucial to power generation applications, which include reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), membrane capacitive deionization (CDI), and reverse electrodialysis (RED). Improved membranes with tailored water and salt transport properties are required to extend and optimize these technologies. Water and salt transport structure/property relationships provide the fundamental framework for optimizing polymer materials for membrane applications. The water and salt transport and free volume properties of a series of sulfonated styrenic pentablock copolymers were characterized. The polymers' water uptake and water permeability increase with degree of sulfonation, and the block molecular weights could be used to tune water uptake, permeability, and selectivity properties. The presence of fixed charge groups, i.e., sulfonate groups, on the polymer backbone influence the material's salt transport properties. Specifically, the salt permeability increases strongly with increasing salt concentration, and this increase is a result of increases in both salt sorption and diffusivity with salt concentration. The data for the sulfonated polymers, including a sulfonated polysulfone random copolymer, are compared to those for an uncharged polymer to determine the influence of polymer charge on salt transport properties. The sulfonated styrenic pentablock copolymer permeability data are compared to literature data using the water permeability and water/salt selectivity tradeoff relationship. Fundamental transport property comparisons can be made using this relationship. The effect of osmotic de-swelling on the polymers and the transport properties of composite membranes made from sulfonated styrenic pentablock copolymers are also discussed. The sulfonated styrenic pentablock copolymers were exposed to multi-valent ions to determine their effect on the polymer's salt transport properties. Magnesium chloride permeability depends less on upstream salt concentration than sodium chloride permeability, presumably due to stronger association between the sulfonate groups and magnesium compared to sodium ions. Triethylaluminum was used to neutralize the polymer's sulfonic acid functionality and presumably cross-link the polymer. The mechanical, transport, and free volume properties of these aluminum neutralized polymers were studied. / text

The structure-property relationships of epoxy nanocomposites with inorganic layer-structure nanofillers have been studied to obtain the fundamental understanding of the role of nanofillers and the physics of polymer nanocomposites in this dissertation. Several polymer nanocomposite systems with modified montmorillonite (MMT) or α-zirconium phosphate (ZrP) nanofillers were prepared with epoxy matrices of different ductility and properties. The successful nanofiller's exfoliations were confirmed with X-ray diffraction and transmision electronic microscopy (TEM). Dynamic mechanical analysis (DMA) on the prepared epoxy nanocomposites revealed the significant increase in rubbery plateau moduli of the epoxy nanocomposite systems above Tg, as high as 4.5 times, and tensile test results showed improved modulus by the nanofiller addition, while the fracture toughenss was not affected or slightly decreased by nanofillers. The brittle epoxy nanocomposite systems were toughened with core shell rubber (CSR) particles and showed remarkable increase in fracture toughness (KIC) value up to 270%. The CSR toughening is more effective at ductile matrices, and TEM observation indicates that major toughening mechanisms induced by the CSR addition involve a large scale CSR cavitation, followed by massive shear deformation of the matrix.

The structure-property relationships of epoxy nanocomposites with inorganic layer-structure nanofillers have been studied to obtain the fundamental understanding of the role of nanofillers and the physics of polymer nanocomposites in this dissertation. Several polymer nanocomposite systems with modified montmorillonite (MMT) or α-zirconium phosphate (ZrP) nanofillers were prepared with epoxy matrices of different ductility and properties. The successful nanofiller's exfoliations were confirmed with X-ray diffraction and transmision electronic microscopy (TEM). Dynamic mechanical analysis (DMA) on the prepared epoxy nanocomposites revealed the significant increase in rubbery plateau moduli of the epoxy nanocomposite systems above Tg, as high as 4.5 times, and tensile test results showed improved modulus by the nanofiller addition, while the fracture toughenss was not affected or slightly decreased by nanofillers. The brittle epoxy nanocomposite systems were toughened with core shell rubber (CSR) particles and showed remarkable increase in fracture toughness (KIC) value up to 270%. The CSR toughening is more effective at ductile matrices, and TEM observation indicates that major toughening mechanisms induced by the CSR addition involve a large scale CSR cavitation, followed by massive shear deformation of the matrix.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19736号 / 工博第4191号 / 新制||工||1646(附属図書館) / 32772 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 村田 靖次郎, 教授 大江 浩一, 教授 小澤 文幸 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Polyesters are an important class of polymers in many applications ranging from common-use objects—such as packaging containers, clothing, and upholstery—to more advanced applications, such as lightweight strength materials in construction, electronics, and automotive parts. Poly(ethylene terephthalate) (PET), a semicrystalline aromatic polyester, is commercially the most common and widely used polyester. However, the inability to reuse polyesters such as PET over multiple reprocessing cycles in the same application remains a challenge due to the susceptibility of the polymer to thermal, hydrolytic, and oxidative degradation during melt processing. The various degradation modes result in a drop in molecular weight, loss of key physical properties, and release of volatile compounds. Furthermore, the vast issue of plastic accumulation and pollution in diverse ecosystems, landfills, and waste streams underscores the burgeoning need to create a closed loop—responsible materials management from the cradle to the grave—through these materials' continual reuse and recycling. Additionally, most feedstock monomers used in polyester synthesis primarily come from fossil fuels. Fossil fuel extraction processes release gases and particulate matter that adversely affect health, climate, and the environment, so finding alternative sources for polyester monomers is paramount. This dissertation addresses key polyester challenges by designing and synthesizing alicyclic polyesters. First, we synthesized a series of alicyclic polyesters using various ratios of two regioisomers of a previously unexplored alicyclic monomer, bicyclohexyldimethanol (BCD). We learned from this alicyclic polyester series that we could tailor properties such as morphology and elongation while raising the glass transition temperatures (Tg) and lower melting temperatures (Tm) of the polymers based on the regioisomer composition. Furthermore, the regioisomer that led to polymers with semicrystalline morphologies inspired us to apply it to PET as a copolymer, with the goal of increasing PET's stability under melt processing conditions by lowering Tm. Next, we synthesized a series of alicyclic copolyesters with different BCD compositions in the polymer. The results showed that the presence of the alicyclic rings of BCD lowers the melting temperature and enhances the stability of the polymer in the melt compared to PET. These results directed us toward synergistically combining the benefits of alicyclic monomers with sustainable biobased monomers to enhance polyester properties, thereby decoupling fossil fuels from polymer feedstock production. Accordingly, we explored naturally ubiquitous, structurally diverse, and chemically modifiable terpenes present in the resin exudate of conifers. Specifically, we derived alicyclic diacid and diol monomers from the terpene verbenone and used them to synthesize a series of biobased alicyclic polyesters. The polymer series exhibited a range of morphologies, Tg's, as well as enhanced stabilities. The semicrystalline composition exhibited higher Tg and slightly lower Tm than PET while possessing exceptional stability in the melt over PET. / Doctor of Philosophy / Polyesters are important materials widely used today. They are very large molecules composed of a basic chemical unit linked together in a repeating fashion to make a long chain. The nature of the links between the basic units is referred to as an ester link, and materials are described as polyester when the number of these links is large. The applications of polyesters range from common-use objects—such as packaging containers, clothing, and upholstery—to more advanced applications in construction, transportation, and defense—such as body armor, seat belts, and lightweight strength materials and coatings in construction. The properties of its basic structural unit enable the wide breadth of applications of polyesters. A significant challenge that faces polyesters is the inability to reuse the material in the same application multiple times. The material must be reprocessed by melting at high temperatures to be reused. This melting breaks down the polyester chain, weakening the material and rendering it unsuitable for continued use. The need to reuse polyesters is an important area of concern because of the growing problem of plastic accumulation and pollution in diverse ecosystems and landfills. If these materials are continually reused, they will not accumulate as environmental waste. Furthermore, the basic starting unit that makes up polyesters largely comes from fossil fuels. Fossil fuel extraction processes release gases and particulate matter that adversely affect health, climate, and the environment. The issues of polyester breakdown in the melt and fossil fuel use to make the polyester can be addressed in two ways. First, reinforcing the polyester through changes to the basic structural unit can prevent the breakdown of the material when melted, thereby enabling its reuse over multiple cycles. Second, reducing the dependence on fossil fuels to make the basic structural unit of the polyester can be accomplished by using more renewable biobased sources instead. This dissertation seeks to address these two challenges. In the first approach, we investigate the effect of using a special cyclic structure in the polyester make-up to reinforce its stability when melted and enable its reuse. Next, we use plant materials to derive these unique structures to reduce the dependence on fossil fuels and mitigate the environmental, climate, and health effects of fossil fuel use.