Advancements in the semiconductor industry have lead to the miniaturization of components and increased power densities, resulting in thermal management issues. Due to this shift, finding multifunctional materials with excellent thermal conductivity and electrical resistivity are becoming increasingly important. For this research thesis, thermally conductive polymer composites were developed and characterized. In the first study, a LLDPE matrix was combined with hBN and SiC to determine the effects of both filler type and filler content. Novel porous composite materials were also fabricated to align thermally conductive fillers, improving k_eff while significantly reducing the overall weight. In the second study, PPS was used as a high performance matrix material and combined with different types of hBN to investigate the effects of size, shape, and aspect ratio on the composite, as well as the effect of hybrid fillers. The composites were characterized with respect to their physical, thermal, electrical, and mechanical properties.

Advancements in the semiconductor industry have lead to the miniaturization of components and increased power densities, resulting in thermal management issues. Due to this shift, finding multifunctional materials with excellent thermal conductivity and electrical resistivity are becoming increasingly important. For this research thesis, thermally conductive polymer composites were developed and characterized. In the first study, a LLDPE matrix was combined with hBN and SiC to determine the effects of both filler type and filler content. Novel porous composite materials were also fabricated to align thermally conductive fillers, improving k_eff while significantly reducing the overall weight. In the second study, PPS was used as a high performance matrix material and combined with different types of hBN to investigate the effects of size, shape, and aspect ratio on the composite, as well as the effect of hybrid fillers. The composites were characterized with respect to their physical, thermal, electrical, and mechanical properties.

Thesis (Ph. D.)--University of Nevada, Reno, 2006. / "December, 2006." Includes bibliographical references (leaves 167-180). Online version available on the World Wide Web.

Fiber and matrix-dominant properties of fiber-reinforced polymer composites are important in many advanced technological fields, such as aviation, aerospace, transportation, energy industry, etc. Still, pre-mixing the polymer matrix with nanoparticles may enhance the through-thickness or matrix-dominant properties, and surface treatment of fiber reinforcements with nanoparticles, on the other hand, may improve the in-plane or fiber-dominated properties of laminated composites, as well as interfacial adhesion. A novel manufacturing method that combines a spraying process with nanoparticle/epoxy mixture technique was introduced to incorporate carbon nanoparticles for enhancement of thermal properties of multiscale laminates. Several graphene-based nanomaterials including graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) were employed to modify the epoxy matrix and the surface of glass fibers. Multiscale glass fiber-reinforced composites were fabricated from unmodified and modified epoxy, as well as fibers, using the vacuum-assisted resin transfer molding (VARTM) process. The composites obtained combined improvements in both the fiber and matrix- dominant properties, resulting in superior composites. The morphological, rheological, thermal and mechanical properties of the glass fiber-reinforced multiscale composites were investigated. The thermal properties of the epoxy/nanoparticle composites were studied through differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and thermal conductivity measurements. The tensile, bending, vibration, interlaminar shear strength (ILSS) and thermal characterization results indicated that the introduction of GNPs, GO, rGO, and MWCNTs enhanced the themo-mechanical properties. The fracture surfaces of the fiber-reinforced composites were examined by scanning electron microscopy (SEM) and the micrographs were analyzed to comment on the mechanical results.

Composites based on binary polymer blends of polystyrene (PS)/poly(ethylene-co-vinyl alcohol) (EVOH) (70/30 wt%) containing natural Montmorillonite, Na-MMTs (Nanomer PGW or Cloisite Na+) and organically modified Montmorillonite clays, OMMTs (Nanomer I.30T, Cloisite 30B or Cloisite 10A) were prepared via melt compounding. The interactions between the polymers and clays were studied using flow micro-calorimetry (FMC). Data obtained from FMC indicated that the probe molecule mimicking EVOH (butan-2-ol) interacted with the MMTs and OMMTs much more strongly than PS. Scanning electron microscopy (SEM) revealed that composites based on binary blends had dispersed/continuous morphologies, in which EVOH was dispersed in a PS matrix. The size of the EVOH droplets in the PS matrix increased with increasing clay loading. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) were used to determine the extent of dispersion and location of clay in the PS/EVOH/clay composites. These techniques confirmed the formation of intercalated clay structures. As predicted by FMC, the clay platelets were selectively located in the EVOH phase, independent of the blending sequence and the type of organic modifier in the OMMT. Composites containing OMMTs showed better dispersion of platelets within the EVOH phase than those containing Na-MMTs. Differential scanning calorimetry (DSC); showed the crystallisation behaviour of EVOH to depend on the clay loading and the nature of the organic modifier in the OMMT. Nanomer PGW, Cloisite Na+ and Cloisite 30B acted as weak nucleating agents. In contrast, Nanomer I.30T and Cloisite 10A significantly hindered the crystallisation of EVOH in the blends due to the restriction of chain segment mobility. Dynamic mechanical thermal analysis (DMTA) confirmed that the presence of clay increases the storage modulus of the composites compared to an unfilled blend. In addition, the improvement in storage modulus reflected the dispersion state of the different clays and their interaction with the polymers of the blend. Ternary-blend based composites were formed by adding poly(styrene-co-acrylonitrile) (SAN) to the composites based on binary PS/EVOH blends. This resulted in a finer dispersion of the EVOH phase and the development of a core-shell morphology, in which SAN encapsulated and formed shells around EVOH droplets. In contrast to binary blend composites, the clay platelets were found at the interface between SAN and EVOH in the ternary blends.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第19320号 / 農博第2141号 / 新制||農||1036(附属図書館) / 学位論文||H28||N4948(農学部図書室) / 32322 / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 西尾 嘉之, 教授 木村 恒久, 教授 髙野 俊幸 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Traditionally it was thought that the unidirectional strength in the fiber direction of fiber dominated composites was not influenced by the matrix material. As long as the fiber was not affected then the strength would remain. However this thesis will challange that belief. The unidirectional strength in the fiber direction of fiber dominated composites is influenced by the matrix material. The object of this study was to examine the quasi-static tensile strength of unidirectional polymer composites, and then use current analytic models to predict the experimental results. The different matrix materials were polyphenylene Sulfide (PPS), vinyl ester with two different fiber-matrix interface materials, and polyether ether ketone (PEEK). / Master of Science

No description available.

Fillers are often incorporated in polymer matrices in order to improve cost, mechanical, thermal, and transport properties. This work explores the hypothesis that pollen, a natural particle, has the potential to be an effective biorenewable reinforcing filler due to its unique surface architectures, high strength, chemical stability, and low density. Pollens from sources such as ragweed plants are ubiquitous natural materials that are based on sustainable, non-food resources. Pollen is a remarkable example of evolutionary-optimized microscale particle with structures and/or chemistries tailored for effective adhesion to a variety of surfaces and protection of genetic material under different dynamic and environmental conditions. The pollen shell is perhaps the most chemically resistant naturally occurring material. As many pollens achieve pollination simply by being carried by wind, they are very light-weight. These properties make pollen an attractive option as a natural filler for polymers. This research aims to characterize pollen interfacial properties and utilize pollen as an effective reinforcing filler in polymer materials. In this work, interfacial properties are characterized using Fourier transform infrared spectroscopy (FTIR), the BET method, and inverse liquid chromatography (ILC). These techniques were useful in determining the effect of surface treatments and further chemical modifications on pollen interfacial properties. Characterizing these properties allowed for improved understanding and utilization of pollen as a filler by revealing the enhanced surface interactions and surface properties of acid-base treated pollens when compared to as received untreated pollens. Epoxy and polyvinyl acetate (PVAc) matrices were used to demonstrate the effectiveness of pollen as a filler, as a function of pollen loading and surface treatments/chemical modifications. Scanning electron microscopy (SEM) was used to determine interfacial morphology, a high throughput mechanical characterization device (HTMECH) was used to determine mechanical properties, and differential scanning calorimetry (DSC) was used to determine glass transition behavior. In epoxy, pollen was an effective load bearing filler only after modifying its surface with acid-base hydrolysis. In PVAc, pollen was an effective load bearing filler only after an additional functionalization with a silane coupling agent. Finally, the species of pollen incorporated in PVAc matrices was varied in order determine the effect of the size of surface nano- and micro- structures on wetting, adhesion, and composite properties. Composites containing pollen displayed enhanced wetting and interfacial adhesion when compared to composites with smooth silica particles. Additionally, it was observed that pollen with smaller surface structures were wetted more effectively by the polymer matrix than pollen with larger structures. However, mechanical properties did not suggest significant changes in interfacial adherence with varied pollen microstructure size. The results of this work highlight the feasibility and potential of utilizing pollen as a natural filler for creating high strength, light-weight polymer composites with sustainable filler.

Cellulose nanocrystals (CNCs) are crystalline nanoparticles that are extracted from renewable sources such as trees or bacteria through mechanical or chemical treatments of their source. CNCs are of interest to several research communities concerned with sustainable technologies. Specifically, CNCs have attracted great interest in the polymer composite community given their high theoretical specific strength and modulus. Two key obstacles surround the use of CNCs in polymer composites, namely their comparatively lower thermal stability and hydrophilicity render their dispersion, and therefore mechanical reinforcement, in polymer matrices challenging. This research considered a waterborne epoxy and a polyurethane elastomer for CNC/polymer composites since these composites are seldom reported in literature or often suffer from degraded mechanical properties. In the epoxy/CNC composites, samples were prepared by two methods, first an epoxy emulsion was mixed with an amine crosslinker and an aqueous based CNC suspension (1-step mixing), and second, the epoxy emulsion was premixed with the aqueous based CNCs and the amine crosslinker was added some time later (2-step mixing). Both composites were mixed by magnetic stirring, however the samples prepared by the 2-step mixing method exhibited enhanced dispersion and mechanical properties, specifically the storage modulus (E’), tensile strength, and work of fracture. Zeta potential measurements and chemical analysis by FTIR indicated that the dispersion mechanism was physical in nature, rather than chemical. In the second composite system, CNCs were chemically modified with an isophorone diisocyanate (IPDI) monomer having unequally reactive isocyanate groups. The goal of the modification step was to react only one isocyanate group with the CNC surface and have a free isocyanate group available for further modification. The chemical structure of one linked isocyanate (urethane bond) and one free isocyanate was confirmed by FTIR and 13C NMR. The particles modified by IPDI (m-CNC) and the neat particles (um-CNC) were incorporated into a polyurethane matrix based on IPDI and a triol crosslinker. Upon visual inspection of the cured composites, it was clear that the modification step produced homogeneously dispersed nanoparticles in the polyurethane while the um-CNCs were aggregated. When the mechanical properties were tested by uniaxial tensile testing, it was determined that the m-CNC composites resulted in improvements in the tensile strength and work of fracture without degradation of the elongation of break property when compared to the neat matrix. Overall the findings in this research highlight important considerations for designing CNC/thermoset composites with enhanced dispersion and mechanical performance.