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Title: Functionalization of carbon fibers by atmospheric pressure plasma treatment for improved self-healing composites
Author: Chen, Wei-Yu
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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This study aimed towards the investigation of using a novel atmospheric pressure plasma (APP) process to introduce carboxylic acid functional groups on carbon fibers (CFs), so the functionalized CFs can react with an ionomer-modified epoxy resin, which was developed in this study, to prepare a self-healing composite. The APP process, which was performed in a bespoke Pyrex chamber, was comprised of an APP surface activation and a subsequent acrylic acid (AAc) vapour grafting. The effects of various APP functionalization parameters, such as grafting time and working gas, on surface wettability, stability and chemical composition, were first investigated on silicon wafers before applying them to CFs. The healing efficiency of the ionomermodified epoxy resin network, and functional group reactions between the ionomer healing agent and the functionalized silicon and CF surfaces, were also studied to estimate the self-healing function. Contact angles of the silicon wafers with water were initially 56.1±0.8° and after APP activation with air and argon 8.2±0.2° and 4.6±0.2°, respectively, and increased to a range between 4.8° to 16.1° after AAc vapour grafting, suggesting the capability of the APP process to control surface wettability and to potentially perform surface deposition. By observation of the binding energy peak at 289.2 eV in the C1s core level spectrum from XPS, the results indicated the presence of carboxylic acid groups on the surfaces, which was also confirmed by 2,2,2-trifluoroethanol derivatization. A 19.72% atomic percentage of carboxylic acid functional groups was achieved, which is higher than the result from a conventional APP process (13.36% by a 60-second APP treatment with AAc vapour directly being injected into the activating zone during the process), compared with the theoretical percentage of pure AAc (33.3%). For the investigation of the ionomer healing system, a healing efficiency of 31.07% was observed on the ionomer-modified epoxy resin network. The functional groups on the ionomer healing agent were proved to be able to react with APP/AAc-grafted carboxylic acid functional groups. In summary, a novel, rapid APP process, which utilizes APP activation and AAc vapour grafting in a bespoke Pyrex chamber, was developed in this study. The APP process was capable of not only tailoring surface wettability but also introducing carboxylic acid functional groups. Combining this novel APP process with the ionomer selfhealing system, a self-healing composite material with potentially enhanced load carrying capacity can be envisaged.
Supervisor: Matthews, Allan ; Jones, Frank ; Leyland, Adrian Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available