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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Synthesis and Characterization of Novel Functional Materials based on Cellulose and Graphene Oxide

Chen, Yian 22 July 2020 (has links)
This thesis focused on the synthesis and characterization of novel functional materials based on cellulose and graphene derivatives. Cellulose/GO hydrogels were produced as the starting material by dissolving cellulose and dispersing GO in NaOH/urea solution. This method is considered as an efficient, simple, environmentally friendly, and low-cost method. Novel functionalities, such as sensing, catalytic and EMI shielding properties have been “built-in” to cellulose/GO hydrogels. Cellulose/rGO composite films and aerogels were successfully fabricated by dissolving cellulose and dispersing GO in NaOH/urea solution, followed by the chemical reduction with vitamin C as the reducing agent. The cellulose/rGO films and aerogels with various rGO contents were prepared by air-drying and freeze-drying of the prepared cellulose/rGO composite hydrogels. The resultant cellulose/rGO composites prepared by this efficient and simple method show high resistance sensitivity to environmental stimuli like temperature, humidity, liquids, vapours, and strain stress. Thus, the cellulose/rGO films can be applied in detecting human motions and human breath cycles. Liquid temperature, liquid type, and ion concentration also be determined by our cellulose/rGO films. Moreover, the composite aerogels are fast responding and extremely sensitive sensors for vapour detection and testing with good repeatability. It was also revealed that discriminating and quantitative responses can be obtained when analyzing various vapours and different vapour concentrations. For methanol vapour, the aerogel shows linear response to the vapour concentration. Thus cellulose/rGO composite aerogel can be used to quantify methanol vapour concentrations. The efficient, scalable, and environmentally friendly preparation of novel and high-performance of vapour sensing materials with well reproducibility is promising to achieve practical vapour sensing applications. We have successfully presented an effective, facial, simple, and scalable method to form Fe3O4 nanoparticles onto cellulose/GO hydrogels. XRD, FTIR, XPS and TEM indicated that Fe3O4 nanoparticles with good dispersion and uniform size are successfully coated on cellulose matrix and GO sheets. This material was tested as catalyst for the cleaning of dye-contaminated water by oxidation with H2O2.The optimized experiment conditions for AO7 degradation are: [AO7] = 0.1 mM, T = 298 K, [H2O2] = 22 mM, and pH = 3. Under these conditions, the resulting hydrogels display 97 % AO7 removal within 120 min and retained strong degradation performance after twenty consecutive cycles of reuse. Especially, the detailed XPS analysis of cellulose/GO/Fe3O4 and cellulose/Fe3O4 composites indicated that the cellulose/GO/Fe3O4 hydrogel retain its high degradation activity by keeping the ratio of Fe3+/Fe2+ at 2 during the 20 heterogeneous Fenton-like reaction cycles. Therefore, the cellulose/GO/Fe3O4 hydrogel is recommended to test the treatment of other dye-contaminated wastewaters. Cellulose/rGO/Fe3O4 films and aerogels were successfully fabricated by the in-situ grown of Fe3O4 nanoparticles within a cellulose matrix containing rGO sheets. Cellulose/rGO (8 wt.%)/Fe3O4 aerogels with the thickness of 0.5 mm exhibited high EMI shielding performance with the EMI SE value at 32.4-40.1 dB in the 8.2-12.4 GHz frequency range. High loading of rGO and large thickness of the composites are beneficial for the excellent EMI shielding performance of our aerogels. The lightweight aerogel is suitable for the practical application as EMI shielding materials such as spacecraft, aircraft, energy conversion application, and energy storage.
2

NOVEL HIGH-RATE MANUFACTURING PROCESS FOR MULTIFUNCTIONAL THERMOPLASTIC COMPOSITES

Jessica Lavorata Anderson (17593293) 11 December 2023 (has links)
<p dir="ltr">In pursuit of enhanced fuel economy, the automotive industry is exploring the substitution of metal components with lightweight polymer composites. These components must withstand elevated static loading and crash performance, while ideally offering added functionalities and reduced weight. To tackle these challenges, this research presents an innovative manufacturing method aimed at reducing costs and cycle times associated with continuous fiber polymer composites. This method involves producing a linear thermoplastic composite rod known as M-TOW (Multi-tow), which can be molded into intricate shapes to serve as tailored structural reinforcement in hybrid-molded parts. The research encompasses the processing of M-TOW, with a focus on predicting consolidation using Darcy’s law, integrating functional components for thermal and electrical conductivity using overbraided metallic wire or sensing using optical fibers, and its application in real-world scenarios. These advancements showcase the versatility and potential of M-TOW in high-rate continuous fiber manufacturing, paving the way for multifunctional hybrid molded structures.<br><br></p>

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