Masters Theses

Dong Zhang

Date of Award

12-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Textiles, Retail, and Consumer Sciences

Major Professor

Gajanan Bhat

Committee Members

Kermit E. Duckett, Larry C. Wadsworth

Abstract

Oriented polyethylene precursors possess extraordinary physical and mechanical properties and a very high carbon content. However, being thermoplastic fibers, they soften and melt at a fairly low temperature, losing their fiber form. The key to success for producing carbon fibers from polyethylene is to introduce crosslinks and make them stable to higher temperatures of carbonization. In this research, an effort was made to produce carbon fibers from a highly ordered and oriented polyethylene fiber. Sulfonation of the fiber was studied as a method of stabilizing this thermoplastic fiber for higher temperatures required for carbonization. The effect of time, temperature and tension during sulfonation was studied systematically. The progress of reactions and the extent of stabilization were studied by thermal analyses (Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA)), burning behavior and color change. Other techniques, such as wide angle x-ray diffraction, fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and optical microscopy were used to investigate the changes in structure and morphology of the fibers with stabilization treatment. Also the physical properties of the carbon fibers produced from these precursors were investigated. It also shown that highly ordered and oriented polyethylene precursor fibers could be stabilized in sulfuric acid bath between 140 to 160 °C after treating for about 75 minutes. DSC studies showed that the melting peak of the stabilized fibers had completely disappeared. TGA indicated that the stabilized fibers retain 50% of their weight at 800 °C, when scanned in a nitrogen environment. The oriented fibers had a strong tendency to shrink before the onset and progress of reactions, and the tension applied during stabilization had a major role in determining the morphology of the stabilized fibers. In the absence of tension, some of the extended chain polyethylene apparently changed to a folded chain structure giving two melting peaks. SEM photographs clearly showed the formation of kink bands due to shrinkage. The stabilized fibers were carbonized at 1150 °C for a four minutes in a nitrogen atmosphere. The carbon yield of the fibers was about 70-80% and the carbon content of the fibers was more than 92%, as seen by elemental analysis. The resultant carbon fibers had good mechanical properties, i.e. a tensile strength of 2.1 GPa and Young's modulus of 210 GPa. The elongation of the fiber at break was less than 1%.

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