Author ORCID Identifier

https://orcid.org/0000-0002-9711-9512

Year of Publication

2021

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Chemical and Materials Engineering

First Advisor

Dr. Rodney Andrews

Second Advisor

Dr. Matthew Weisenberger

Abstract

Carbon fiber is an ideal material for structural applications requiring high strength and stiffness and low weight. Yet it has seen only incremental improvements in properties over the last few decades. Carbon fibers remain limited in attaining their theoretical tensile strength and modulus, largely due to defects in their structure, some of which stem from the fiber production process itself. Through the mitigation of defect formation as well as approaches to decrease fiber linear density, it is hypothesized that carbon fiber with enhanced specific properties, including specific strength and modulus, could be produced which would significantly propel its unique capabilities.

One approach to produce high specific property carbon fibers is the development of hollow carbon fibers. The development of hollow carbon fibers for use in structural applications has not been widely explored. The most successful methods to date rely on multicomponent spinning with sacrificial polymers and complex spinneret geometries. A more simplistic, scalable, and economical approach is the use of a segmented arc - shaped spinneret. Traditionally, segmented arc spinnerets have been used for melt or dry spinning hollow fibers. To the author’s knowledge, only three references exist describing its use in a solution spinning process for the production of hollow fiber precursors from polyacrylonitrile (PAN). The development of structural hollow carbon fibers from such precursors represents a new technology requiring extensive research in the development of the hollow fiber precursors, as well as their subsequent oxidation and carbonization.

In this work, a method for the multifilament spinning of hollow PAN fibers using a segmented arc spinneret is described. This includes the coagulation, washing, drawing, and spooling of PAN hollow fiber and the effect of each on hollow fiber formation, structure, and properties. In particular, the impact of the coagulation bath composition is explored. Here, the resultant hollow fibers approached the specific tensile performance of traditional solid precursors.

Utilizing these continuous tows of multifilament PAN hollow fibers, oxidation studies were undertaken to determine the capability of the hollow filaments, aided by oxidation from the interior, to oxidize at an increased rate compared to traditional solid fibers. The impact of open interior volume as a percent of the total fiber volume on oxidation was studied. In addition, the mechanisms behind the development of a skin-core structure in the hollow fiber wall are explored and mitigation methods proposed.

The final part of the work focuses on the carbonization of oxidized hollow fibers. The structural parameters of hollow carbon fibers are compared to commercially available solid carbon fibers, with their resulting specific tensile properties compared. A direct comparison is made between hollow fibers and solid fibers with similar outer diameter with regard to their oxidation, carbonization, and resulting morphology and tensile performance. Finally, recommendations are made for continued improvement of the precursor, oxidized, and carbonized hollow filaments to achieve smaller precursor dimensions, faster oxidation rates, less skin-core formation, and higher specific tensile properties.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.427

Funding Information

Financial support for this work was provided by the Department of Energy Office of Energy Efficiency and Renewable Energy Hydrogen and Fuel Cell Technologies Office (award number DE-EE0008095) from 2017-2020.

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