Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Electrical and Computer Engineering

Additive manufacturing (AM) technology is rapidly advancing across diverse fields. For instance, the use of robotic arms in various AM processes has led to significant gains in printing flexibility and manufacturing scalability. However, despite these advancements, there remains a notable research gap concerning the mechanical properties of parts 3D-printed with robotic arms. This study focuses on developing a robotic fused filament fabrication (FFF) 3D-printing process with a layer resolution of 50 μm to 300 μm. The impact of the robotic printing process on the mechanical properties of printed parts is investigated and benchmarked against a commercial FFF 3D printer. In addition, we propose a novel tool path that can vary contour layer thickness within an infill layer to improve mechanical strength by minimizing air gaps between contours. SEM images suggest that this new tool path strategy leads to a significant reduction in the fraction of the void area within the contours, confirmed by a nearly 6% increase in the ultimate tensile strength. Furthermore, a novel strategy for non-planar contours is proposed, specifically designed for thin-shell 3D models. This approach aligns tool paths parallel to the Z-axis, organized into triangular segments, and utilizes planar slicing techniques. The method involves segmenting the point cloud and systematically printing non-planar contours on top of the planar contours. Axial compression testing reveals that samples produced using this strategy exhibit mechanical properties comparable to those of conventional 3D printing. However, distinct fracture patterns are observed: in conventional 3D-printed samples, fractures occur on both inner and outer surfaces, while in non-planar printed samples, fractures are confined to the inner surfaces (planar contours) and do not propagate to the outer non-planar contours. This demonstrates the potential of non-planar printing for improved structural integrity.

Committee: Raul Ordonez Dr. (Advisor) Subjects: Electrical Engineering; Mechanical Engineering; Plastics; Robotics

Bachelor of Science (BS), Ohio University, 2024, Chemistry

Petroleum-based plastic has caused devastating effects on the health of the natural world and people from its derivation from non-renewable resources and complex recycling processes. Polylactic acid (PLA) is a bio-based plastic that has the potential to alleviate these issues. In this experiment, the ring-opening polymerization of lactide to PLA is catalyzed by two organic catalysts, resulting in a low molecular weight polymer with a degradation temperature around 300 – 340 °C and glass transition temperatures between 27 and 33 °C. The polymer is successfully degraded upon exposure to 50 % aqueous ethanol at high temperatures, resulting in a decrease in theoretical number average molecular weight. With further research, PLA exhibits considerable potential for chemical recycling to close the loop of the production process and achieve a circular economy.

Committee: Lauren McMills (Advisor); Katherine Cimatu (Advisor) Subjects: Chemistry

Master of Science in Mechanical Engineering, Cleveland State University, 2023, Washkewicz College of Engineering

This research investigates the deformation recovery of 3D-printed Polylactic Acid (PLA) shape memory polymers (SMPs). The study delves into the influence of Fused Deposition Modelling (FDM) parameters, such as nozzle temperature, layer thickness, and printing speed, on the thermomechanical behavior of PLA SMP honeycomb structures. The research identifies optimal printing conditions using the Taguchi approach and explores the cyclic shape memory recovery behavior of the optimized PLA SMP under compression loads. Additionally, the research includes a chapter on the extrusion and printing of uniform-diameter polylactic acid carbon fiber (CFR-PLA) composite filaments. The synthesis of CFR-PLA involves planetary ball milling for composite homogeneity. Extrusion parameters and 3D printing conditions are optimized, and mechanical testing, particularly tensile testing, reveals the composite's strength and flexibility. Fracture surface analysis highlights the behavior of carbon fibers during testing. Altogether, these results advance our understanding of PLA shape memory polymers and CFR-PLA composites, offering insights into material properties, printing parameters, and potential applications in various industries, including robotics, aerospace, and biomedicine.

Committee: Dr. Prabaha Sikder (Advisor); Dr. Mustafa Usta (Committee Member); Dr. Josiah S Owusu Danquah (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2023, Materials Engineering

Additive manufacturing (AM) has evolved as a convenient technology for rapid fabrication of prototype tooling and complex geometry components. Among all AM techniques, FFF is the most widely used for making polymeric structures. However, the process consistency and control of properties in the manufactured articles remains a challenging issue. The current study aims to investigate physical changes in polylactic acid (PLA) during 3D printing. The correlations between porosity, crystallinity and mechanical properties of the printed parts were studied. Moreover, the effects of bed-plate temperature were investigated. Experimental results confirmed the anisotropy of printed objects due to the occurrence of orientation phenomena during filament deposition and the formation both of ordered and disordered crystalline structures (α and δ, respectively). A post-3D printing heat treatment cycle was demonstrated as an effective method to improve mechanical properties by optimizing the crystallinity (transforming the α form into the δ form) and overcoming the anisotropy of the 3D printed object. The second approach to enhance the physical and chemical properties of neat PLA is by using nano-additives such as carbon nanotubes (CNTs) and carbon black (CB). 4 As the concentration of carbon nanotubes increased the mechanical and electrical properties were improved even with low volume ratio of CNTs. In molten polymer and under shear force CNTs tended to align parallel to the shear direction leading to significant increase in electrical properties in the direction of alignment. Also, a change in the enthalpy of cold crystallization was observed. The enthalpy of cold crystallization of PLA/CNT samples was lower than pure PLA because of a change in the type of crystallites formed during cold crystallization. The presence of carbon nanotubes reduced the crystallization domain leading to the formation of unstable crystalline phase δ, which was remarkably disordered compared to that o (open full item for complete abstract)

Committee: Khalid Lafdi (Committee Chair); Youssef Raffoul (Committee Member); Donald Klosterman (Committee Member); Li Cao (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Akron, 2018, Polymer Science

The synthesis of cyclic monomers based on 2-bromo-3-hydroxypropionic acid starting material was investigated to produce poly(lactic acid-co-2-bromo-3-hydroxypropionic acid) by a ring-opening approach. The synthesis of cyclic(lactic acid-co-2-bromo-3-hydroxypropionic acid) was examined and characterized by mass spectrometry. Six-membered O-carboxyanhydrides were attempted to be synthesized from 3-hydroxypropionic acid starting materials, which lead to the adventitious synthesis of 2-(chlorocarbonyl)ethyl chloroformate (CFEO). This CFEO molecule was reacted with various aliphatic diols to form poly(ester carbonate)s. The hydrolysis of these materials in basic conditions were investigated. Finally, the functionalization of the poly(lactic acid-co-2-bromo-3-hydroxypropionic acid) and the poly(ester carbonate)s were examined utilizing atom transfer nitroxide radical (ATNRC) and atom transfer radical polymerization (ATRP) techniques.

Committee: Coleen Pugh (Advisor); Li Jia (Committee Chair); Matthew Becker (Committee Member); Chrys Wesdemiotis (Committee Member); David Modarelli (Committee Member) Subjects: Polymer Chemistry

BA, Oberlin College, 2018, Environmental Studies

Plastic straws are one of the most abundant items found in oceans and coastal cleanups around the United States and internationally. Plastic does not decompose over time, so all the plastic we have ever made is still around, affecting every ecosystem on the planet. Drinking straws are made of 100% recyclable material, but because of their small size most recycling plants are not able to process them so they are sent to landfills. Petroleum-based plastic production is also a large source of greenhouse gas (GHG) emissions, making up 1-3% of the United States' carbon emissions alone. By considering green alternatives to PP drinking straws, we can see if there actually are affordable alternatives that can help reduce plastic waste and carbon emissions. This case study focuses on the Feve, a restaurant in the City of Oberlin, and aims to understand the cultural significance of drinking straws in town, and uses that information to suggest ways of changing straw distribution behavior and minimize plastic waste. This study also compares the environmental and financial costs of the Feve using petroleum-based polypropylene (PP) drinking straws versus “greener” alternatives by constructing a modified life cycle analysis to determine if switching to biodegradable polylactic acid (PLA) plastic drinking straws decreases the Feve's carbon and plastic waste footprint. By tracing GHG emissions created in the production of plastic resins, transportation of materials and products, and disposal of plastic straws, I compare the carbon footprint of three products to see if one is better for the environment than the others. I hope this study can be used as a model to help other restaurants make plans to reduce their plastic waste and carbon footprint at an affordable cost.

Committee: Cynthia McPherson Frantz (Committee Co-Chair); Roger H. Laushman (Committee Co-Chair) Subjects: Business Costs; Climate Change; Comparative; Conservation; Energy; Environmental Economics; Environmental Education; Environmental Science; Environmental Studies; Gases; History; Management; Marketing; Petroleum Production; Plastics; Polymers; Psychology; Sanitation; Social Psychology; Social Research; Sustainability; Transportation

PhD, University of Cincinnati, 2016, Engineering and Applied Science: Materials Science

A drug delivery device (micro-implant) providing sustained release of hydrophilic drugs has the potential to improve the therapeutic outcome for treatment of vitreoretinal (VR) diseases such as primary intraocular lymphoma, uveitis and proliferative retinopathy. At present, the preferred treatment of VR diseases is intravitreal methotrexate (MTX) injection. Each intravitreal injection of MTX is associated with potentially toxic and sub-therapeutic MTX concentrations. Repetitive intravitreal injections are required to maintain therapeutic MTX concentration. A drug delivery system is desired for sustained therapeutic release (0.2-2.0 µg/day) of MTX for >1 month to achieve effective treatment of VR diseases. In an in vitro study, chitosan (CS) and polylactic acid (PLA)-based micro-implants were fab-ricated for different MTX loadings (10%, 25% and 40% w/w). The micro-implant structure was characterized using optical and scanning electron microscopy, time of flight-secondary ions mass spectroscopy and differential scanning calorimetry techniques. The MTX release rate studies were evaluated using a UV-Visible Spectrophotometer. It was observed that uncoated CS-MTX micro-implant released MTX rapidly (~1 day) because of the hydrophilic nature of both CS and MTX. However, the CS-MTX micro-implant with a lipophilic coating of PLA showed therapeu-tic MTX release (0.2–2 µg/day) for >50 days. The MTX release kinetics from the coated micro-implants is explained by a) the Korsmeyer Peppas and zero order model fit (R2~0.9) of the first 60% of MTX release which indicates the swelling of polymer and initial burst release of MTX; and b) the first order and Higuchi model fit (R2 ~ 0.9) from the 10th day to the end of drug release, implying the therapeutic MTX release depends on its concentration and follows diffusion kinetics. The pharmacokinetics and toxicity of the PLA-coated CS-MTX micro-implant (40% w/w MTX) was evaluated in rabbit eyes. High performance liq (open full item for complete abstract)

Committee: Rupak Banerjee Ph.D P.E. (Committee Chair); Zelia Correa M.D. Ph.D. (Committee Member); James Augsburger M.D. (Committee Member); Relva Buchanan Sc.D. (Committee Member); Jude Iroh Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Akron, 2015, Polymer Science

Poly(lactic acid) (PLA), is used in a wide variety of applications. It is a well studied polymer and offers many advantages, such as being derived from renewable resources, being biodegradable, FDA approved for biomedical applications, and commercially available. The main synthetic drawback is that the only sites for post-polymerization functionalization are at the two end groups. By incorporating 3-hydroxy-2- bromopropionic acid as a co-monomer with lactic acid, a site for post-polymerization functionalization can be added. Since the halogen is alpha to a carbonyl, it is activated toward nucleophlic substitution, radical formation, and enolate chemistry. The spacing on the backbone of our polymer allows for additional functionalization including rearrangement, electrophilic aromatic substitution, and cationic ring-opening polymerization.

Committee: Coleen Pugh Dr. (Advisor); Robert Weiss Dr. (Committee Chair); Mathew Becker Dr. (Committee Member); William Landis Dr. (Committee Member); Yang Yun Dr. (Committee Member) Subjects: Chemistry; Polymers

Master of Science (MS), Ohio University, 2014, Civil Engineering (Engineering and Technology)

This thesis evaluates the effects of graphite based carbon nanofibers (CNF) when incorporated within a NatureWorks Ingeo 3001D Polylactide (PLA) matrix. A film casting method was conducted in which CNF was mixed via sonication with neat PLA at 1% wt., 3% wt., and 5% wt. doses in aims of enhancing nanomechanical behavior and conductivity. A melt compounding method via twin extrusion, was also performed to fabricate PLA/CNF samples at the same CNF wt. doses as employed by the film casting method. Nanocharacterization of samples were performed via Atomic Force Microscopy (AFM) and Scanning Electron Microscopy to evaluate nanomechanical properties and nano/micro structure of PLA/CNF samples. The PLA/1%wt. CNF sample mechanically performed better than the neat PLA, 3%, and 5% CNF samples for the film cast (69,996.94 ± 4,545.29 psi) and extruded (95,111.72 ± 30,388.96 psi) methods with respect to AFM nanoindentation. Macroscale tensile testing was performed effectively extruded samples in which the PLA/3%wt. CNF loading case (Young's Modulus = 295,594.18 psi) performed the best. Conductivity measurements were also completed to evaluate the potential for PLA/CNF based nanocomposites to be considered electrical sensors for civil engineering applications. The PLA/5%wt. CNF film cast sample was found to possess the most favorable electrical resistance (859.45 O), while all other samples were deemed not conductive due to improper dispersion of CNF particulates.

Committee: Munir Nazzal Ph.D (Advisor); Savas Kaya Ph.D (Committee Member); Kenneth Walsh Ph.D (Committee Member); Douglas Green Ph.D (Committee Member) Subjects: Civil Engineering

BS, Kent State University, 2014, College of Arts and Sciences / Department of Chemistry and Biochemistry

This thesis overall entails the synthesis and characterization of several novel zinc coordination complexes in attempt to develop alternative Zn catalysts for the ROP of LA. Chapter II described the synthesis and characterization of several zinc thiolate complexes supported by the 1,1,3,3- tetramethylguanidine (H-TMG) ligand. These compounds were synthesized in a very straightforward reaction with diethylzinc, the corresponding thiol, and H-TMG. Reaction of compound 2 yielded an isopropoxide bridged complex that is a proposed intermediate for the ROP of PLA. Chapter III described the preliminary synthetic routes toward the synthesis of polydentate base tethered ligands. Reaction of a dilithiated 2-bromo-4,6-di-tert-butylphenol with dimethylcyanamide was shown to undergo elimination to yield compound 4. This elimination product had not been observed in previous methods for the synthesis of 1,1,3,3-tetraalkylguanidines (HTAG). Finally, Chapter IV described the reactivity of these zinc thiolate compounds and base tethered polydentate complexes in the ROP of LA as well as a method for determining the tacticity of the PLA polymers. Results showed no change in neither reactivity of the zinc thiolate compounds nor stereochemical control of the reaction relative to the zinc aryloxide compounds. The polymerization using the Zn complex with the base tethered ligand requires additional work to completely evaluate its utility.

Committee: Scott Bunge Dr (Advisor); Paul Sampson Dr (Committee Member); Nicola Brasch Dr (Committee Member); Artem Zvavitch Dr (Committee Member) Subjects: Chemistry; Inorganic Chemistry; Polymer Chemistry

MS, Kent State University, 2012, College of Arts and Sciences / Chemical Physics

This work reports on the fabrication and studies of highly piezoelectric composite fibers. The polylactic acid fibers embedded with barium titanate were created using the standard electrospinning method and utilized the high electric fields required for the electrospinning process. Fibers with micron and sub-micron diameters were spun together to produce fibrous mats. These fibrous mats were analyzed for both their direct and converse piezoelectric properties. The converse piezoelectric effect was measured by applying both DC and AC fields to see the electromechanical response of the mats by looking at the movements of the mats. Along with this, the direct piezoelectric effect was measured by applying mechanical forces to the mats, and measured its electrical response. It was found that the piezoelectric coupling constant of the fibrous mat is larger, per weight, than that of single crystal barium titanate films. These materials, unlike the crystalline films, are flexible and can be beneficial in such things as bio-sensors, artificial muscles, and energy harvesting devices. Along with being flexible, the electrospinning process can be used to make similar composite fibers with materials tailored to a desired need, allowing for a multitude of applications to be considered for this method of creating piezoelectric composite fibers.

Committee: Antal Jakli (Advisor); John West (Advisor); Hiroshi Yokoyama (Committee Member); Chanjoong Kim (Committee Member) Subjects: Physics