Author ORCID Identifier

https://orcid.org/0009-0001-6945-8883

Date Available

12-9-2024

Year of Publication

2024

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Engineering

Department/School/Program

Chemical and Materials Engineering

Advisor

Dr. Matthew Weisenberger

Abstract

For decades carbon fiber-based composites have been most heavily employed in lightweight, structural applications where low density and high strength are necessary, most notably within the aerospace industry. However, the advancement of carbon fiber into a wider array of industries has largely been limited by the high financial and energetic costs associated with its manufacture. Moreover, with an increasing societal emphasis on sustainability, there is an ever-growing desire for low-energy carbon fiber production pathways. One such pathway is the conversion of precursor fiber to carbon fiber by direct carbonization, wherein the energy-intensive, pre-carbonization stabilization step is omitted from the carbonization process. For many precursors, including polyacrylonitrile (PAN) and pitch, the stabilization step is required to achieve a thermally stable chemistry that prevents fusion and excessive volatilization of fibers during high temperature carbonization. However, there do exist precursors that are inherently suited for direct carbonization. The literature has historically and broadly posited that aromatic polymers with oxygen functional groups are those which can be directly carbonized, yet also has presented a number of precursors that except these criteria, effectively obfuscating what it means for a precursor to be “stable” and “ready for carbonization.” Drawing upon the known characteristics of precursors for direct carbonization, three new precursor fibers were wet-spun and directly carbonized in this work, each with unique characteristics that provide specific insights into the mystery of direct carbonization. The three precursors herein studied are PEDOT:PSS, n-PBDF, and PSS.

As electrically conductive conjugated polymers, PEDOT:PSS and n-PBDF both possess aromatic backbones with oxygen or sulfur functional groups and are thus meet the traditional criteria for direct carbonization. Their carbonization behavior and resultant carbon fiber properties, including yield, tensile strength and modulus, electrical conductivity, and crystal structure, are evaluated with respect to precursor properties and carbonization temperature, and in comparison to one another. Interestingly, the amorphous PSS in PEDOT:PSS was believed to contribute to the final carbon fiber structure, and therefore its carbonization behavior in its pure form was explored further. As no prior evidence of wet spinning of PSS, a classic polyelectrolyte, was found, the development and properties of precursor PSS fibers were studied in this work. Then, PSS fibers were directly carbonized and their carbon fiber properties are evaluated, with special respect to the precursor PSS counterion, which is shown to have a significant impact on the material’s suitability for direct carbonization.

Overall, this work expands what is known about precursor suitability for direct carbonization by studying the behavior of three new precursors. In this way, steps can be made toward realizing lower energy carbon fiber by means of direct carbonization.

Finally, a novel technique is described for wet spinning multifilament PEDOT:PSS tows, which historically has resulted in fused, inseparable filaments not suitable for the scale-up required for textile applications. In this work, PEDOT:PSS filaments are spun upward into formic acid for coagulation, dried by evaporation, and collected as a multifilament tow at high throughput. The engineering of this spinning technique and the resultant fiber properties is detailed.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.456

Funding Information

  • Department of Energy Hydrogen and Fuel Cells Technology Office (Award number: DE-EE0009241), "Low-Cost, High-Strength Hollow Carbon Fiber for Compressed Gas Storage Tanks"
  • Advanced Fiber Technologies Inc., "Phase 3: Multifilament Spinning of PEDOT Fibers: Electrical conductivity stability"
  • Advanced Fiber Technologies Inc., "Continued Investigations into the Development of Fibers for Electrical Applications - Multifilament Spinning of High Conductivity PEDOT Fibers
  • University of Kentucky Research Priority Area (m-RPA), "Multifilament spinning of PEDOT:PSS conductive fibers toward electronic textile applications"
  • University of Kentucky Center for Applied Energy Research

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