Doctor of Philosophy, Case Western Reserve University, 2019, Macromolecular Science and Engineering

This dissertation has a primary focus on design and development of composites by employing processing methods aimed at improving filler dispersion in polymers. Mixing elements taking advantage of extensional dominated flows are adopted. Several such mixing elements, extensional mixing elements (EMEs) to be specific, with varying degree of ability to impose extensional dominated flows, have been experimentally validated. A first attempt is made to enhance the dispersion of carbon black (CB), graphene nano platelets (GNP) and carbon nano tubes (CNT) in polypropylene (PP). Enhanced dispersion does translate into improved mechanical properties. A more comprehensive approach is adopted with an integrated computational and processing method on thermoplastic polyurethane (TPU) graphene oxide (GO) composites. The role of filler functionalization in exfoliation and TPU hard block crystallization is established. A difference in anisotropy and phase separation is observed between material processed with EME and kneading blocks. A significantly enhanced ductility is obtained by employing EME during processing. Improved abrasion and strength is also observed. A secondary focus of the thesis includes synthesis of composites by wet chemical and other processes to end up with composite materials with enhanced properties and/or improved material behavior. Hydrogels of poly(ethylene glycol) methyl ether methaycrylate filled with graphene oxide are made via a reversible assisted fragmentation termination (RAFT) approach. Reinforcement and lubrication effects are studied with the incorporation of covalent bonds between filler and matrix. Aerogels obtained from hydrogels of graphene oxide (GO) and montmorillonite (MMT) clay nanocomposites in poly(vinyl alcohol) are synthesized. Hence, obtained aerogels have improved compressive strength and further silylation makes them functional materials for oil-water separation. Twin-screw reactive extrusion of Thermoplastic polyureth (open full item for complete abstract)

Committee: Joao Maia (Advisor); Manas-Zloczower Ica (Committee Member); Dai Liming (Committee Member); Lewandowski John (Committee Member) Subjects: Analytical Chemistry; Chemistry; Design; Engineering; Materials Science; Nanoscience; Nanotechnology; Polymer Chemistry; Polymers

Doctor of Philosophy in Engineering, Cleveland State University, 2022, Washkewicz College of Engineering

Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) with superior mechanical, thermal, chemical, and electrical properties are appealing reinforcements for the fabrication of lightweight, high-strength, and wear-resistant metal matrix composites with outstanding mechanical and tribological performance. The nickel-carbon nanotube composites (Ni-CNT) and nickel-graphene nano-platelet composites (Ni-GNP) were processed using two separate ball milling methods, namely dry ball milling (DM) and solution ball milling (SBM), and then sintered using the spark plasma sintering (SPS) technique. The influence of the premixing process, milling time, reinforcement morphology, and concentration on matrix grain size, microstructure, dispersion in the nickel matrix, mechanical properties, and tribological performance of these composites was studied and compared to SPS processed monolithic nickel. The influence of different structural morphologies of CNTs and GNPs on the wear performance and coefficient of friction of these composites was studied using ball-on-disc tribological testing. After the addition of CNTs/GNPs to the nickel matrix, the experimental findings show significant grain refinement and improvement in the microhardness of these composites. The uniform distribution of reinforcement inside the nickel matrix, the finer grain size, and the strong nickel-reinforcement interfacial bonding, which efficiently transfers stress during tensile deformation, are principally responsible for this improvement in these nanocomposites. Various strengthening mechanisms related to CNT-metal matrix composites have been extensively discussed. Using micromechanical models, we have tried to quantify the contribution of these strengthening mechanisms. Moreover, compared to the pure nickel sample, the CNTs and GNPs successfully generated a lubricant layer, improved wear resistance, and reduced friction coefficient during the sliding wear test. When the CNT/GNP-reinforced composites were (open full item for complete abstract)

Committee: Tushar Borkar (Advisor); Majid Rashidi (Committee Member); Rajeev Gupta (Committee Member); Prabaha Sikder (Committee Member); Petru Fodor (Committee Member) Subjects: Aerospace Materials; Materials Science; Mechanical Engineering

PhD, University of Cincinnati, 2018, Engineering and Applied Science: Mechanical Engineering

TiC nanoparticles (NPs) and GNPs(GNPs) are used to reinforce Inconel 718 (IN718) via selective laser melting process. Various post heat treatment methods with four levels of temperature, with or without the subsequent aging are carried out on the obtained pure IN718 and IN718-matrix nanocomposite materials. The effect of post heat treatment strategies on the microstructure and mechanical properties of the obtained materials is investigated. Meanwhile, multiscale simulation is performed to investigate the influence of laser parameters on the microstructure of SLM-processed Ni-Nb alloy, with the consideration of realistic thermal history and powder-to-dense phase transformation. The interaction between particle and solidification front is investigated, the engulfment/push behavior and overall distribution of TiC nanoparticles (NPs) in the dendrite solidification process of the binary alloy are revealed. It is found that with the increase of nTiC addition, the material microstructure is refined. Mechanical properties, including tensile, and anti-wear properties are effectively enhanced with the addition of external nano reinforcement. Multiscale numerical study proves that laser scan speed and degree of undercooling significantly affect the microstructure and overall distribution of NPs in a metal matrix. Higher laser scan speed results in higher cooling rate in the solidification region and alleviated micro-segregation ratio. A higher degree of undercooling leads to easier engulfment of NPs and overall more uniform distribution of NPs.

Committee: Jing Shi Ph.D. (Committee Chair); Jay Lee Ph.D. (Committee Member); Yijun Liu Ph.D. (Committee Member); Vijay Vasudevan Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 0, Polymer Engineering

The dispersion of nanofillers in polymers has been the biggest challenge in exploiting the full use of the nanocomposites. The purpose of the present study is to investigate the effect of ultrasonically aided extrusion in improving the dispersion of various nanofillers in the polymer composites. In the study, polyetherimide (PEI)/graphite, polypropylene (PP)/carbon black (CB), PP/carbon nanotube (CNT) and PP/graphene nanoplatelet (GNP) composites were prepared using a twin screw extrusion without and with imposition of ultrasonic waves. Three different screw configurations were designed to study the efficiency of ultrasonic treatment in the extrusion. Two compounding methods were utilized in preparing the PP/CNT composites. One is the direct compounding (DC) method and the other one is the masterbatch dilution (MD) method. The efficiency of nanofiller dispersion in these two methods was compared. Four kinds of PP of different molecular weight and molecular weight distribution were used in preparation of PP/CNT composites. The mechanism of ultrasonic cavitation was also investigated. The rheological, mechanical, thermal and electrical properties and morphology of all the PP composites were systematically studied to elucidate the processing-structure-properties relationship. The simulation of the nonlinear rheological behavior of PP/CNT composites was carried out. The results showed that the ultrasonic treatment is more efficient in improving the dispersion of expanded graphite (EG), CNT and CB than GNP and original graphite in polymer matrix. Among the three screw designs, the dispersion of nanofillers in polymer was found to be more related to the presence of kneading elements than the reverse elements and residence time. At higher pressure in the ultrasonic zone, the degradation of PP was less severe than at lower pressure. The ultrasonic treatment had a more prominent effect in improving the dispersion in the MD method than in the DC method. In the MD method, t (open full item for complete abstract)

Committee: Avraam Isayev Dr. (Advisor) Subjects: Plastics; Polymers

PhD, University of Cincinnati, 2013, Engineering and Applied Science: Environmental Engineering

CNT are known to have a high-mass transfer capacity for fast-flow rates at low pressure systems which make them desirable for water ultrafiltration. USEPA established regulating limits when copper levels exceed 1.3 mg/L. Copper contamination depends on corrosion reactions, stagnation of water and age of copper pipes, acidity and temperature of the water. In many cases, the pH drops after leaving the distribution systems, which can cause disruption of passivation films and pitting of copper pipes with metal precipitation or dissolution in the household water stream. CNT surface is usually chemically modified to improve desired properties, such as colloidal stability, surface charge and purity. Alcohol (OH) and acid (COOH) network forces formed within functionalized CNT bundles can define their aggregate state and adsorption mechanisms. The adsorption kinetic suggested a two-step process: electrostatic attraction of Cu(II) to oxygen-negatively- charged CNT surface causing deprotonation followed by chemisorption. The adsorption rate was dependent on the concentration of Cu(II) and amount of reactive functional groups on the surface. The adsorption capacity was improved after treating COOH-CNT with alkaline solution, by deprotonating the surface groups and reducing the strong COOH network forces. There is a significant decrease in adsorption capacity of COOH-CNT in the presence of Cl-, but it did not affect OH-CNT. SEM/EDS images showed adsorption of Cl- to pristine-CNT due to its positively charged walls. Extensive washing experiments evaluate the amount of residual impurities leached from CNT, followed by thermodynamic analysis simulations identifying possible CNT near-surface chemistry affecting copper adsorption. In this dissertation, a systematic correlation method was developed to identify chemisorption mechanisms on CNT using converted FTIR absorbance curves of as-received and hybrid CNT (with adsorbed copper) and pure reagent grade CuO (open full item for complete abstract)

Committee: George Sorial Ph.D. (Committee Chair); E Sahle-Demissie Ph.D. (Committee Member); Dionysios Dionysiou Ph.D. (Committee Member); Margaret Kupferle Ph.D. P.E. (Committee Member) Subjects: Environmental Engineering