Date of Award

12-2014

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor

David J. Neivandt

Second Committee Member

Douglas W. Bousfield

Third Committee Member

Barbara J. W. Cole

Abstract

The present work investigates the feasibility of utilizing lignin to produce carbon nanofiber via an ice templating method, with subsequent carbonization. Lignin is a readily available, renewable, and underutilized biopolymer that has recently been investigated as an alternative feedstock material for carbon nanofiber production. Carbon nanofiber is of great interest to scientists and engineers in fields such as materials science, composites, and energy storage due to its unique chemical, physical, and mechanical properties. It is shown in the present work that carbon nanofiber may be generated from lignin via rapid freezing, freeze drying, and carbonization.

An understanding of the effect of various freezing parameters on the morphology of the templated polymer solution was developed. It was determined that a solution film of~100 pm thickness must be generated upon a surface cooled to cryogenic temperatures in order to generate a uniform, nanofibrous polymer morphology. A rapid freezing device was developed for the purpose of rapidly freezing the aforementioned thin film of solution. The device comprised a metal drum attached to a variable speed motor, a solution delivery system, a liquid nitrogen tank and delivery hose equipped with a phase separator, and a cooled storage chamber. Proper operation of the rapid freezing device was shown to result in the production of lignin nanofibers with diameters of less than 100 nm, as determined by scanning electron microscopy. Such a nanoscale fibrous morphology has not been previously observed in traditional ice templating processes, due to the relatively slower freezing rates employed compared to those achieved in the present work. Subsequent freeze drying and carbonization yielded carbon nanofiber with diameters of similar magnitude. The methodology is not specific to lignin; nanofibers of other water soluble polymers including poly(acrylic acid), polyacrylamide, and carboxymethylcellulose have been successfully produced. A mathematical model of the freezing process was developed in conjunction with an economic model to determine ideal operating conditions for the process. The mathematical model was verified experimentally.

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