(103f) A Method for the Sustainable Synthesis of Carbon Fibers Using Dielectrophoresis of Bacteria and Pyrolysis

A Method for the Sustainable
Synthesis of Carbon Fibers using Dielectrophoresis of Bacteria and Pyrolysis

Devin Keck, Monsur Islam and
Rodrigo Martinez-Duarte

Mechanical Engineering
Department, Clemson University

Clemson, SC, USA

Presented
here are preliminary experiments facilitating the use of the
cellulose-extruding bacteria Gluconoacetobacter xylinus as a sustainable
tool for the production of carbon fibers. G. xylinus has the inherent ability
to convert different kinds of sugars into highly crystalline cellulose
nanofibrils. The random movement of the bacteria within the cellulose culture
leads to a porous cellulose scaffold with no apparent order. Additionally, bacterial
cellulose has higher purity and exhibits superior mechanical properties when
compared to the cellulose extracted from plants[1].

Results
presented in previous years focused on how the heat treatment of cellulose
scaffolds functionalized with metal precursors yielded a porous tungsten
carbide. Currently, we are focusing on the positioning of G. xylinus cells
using Dielectrophoresis (DEP) to grow cellulose fibers from specific locations,
which will then be carbonized to create individual carbon fibers. DEP refers to
the movement of electrically polarized cells in response to a non-uniform
electric field of specific frequency and magnitude. Specifically, positive DEP
will be used here to position the G. xylinus cells onto planar
electrodes. The bacteria will be perfused in a continuous flow of nutrient-rich
media, allowing for the continuous extrusion of straight fibers. The ultimate goal
is to develop a scalable platform for the continuous production of cellulose
nanofibers that can then be converted to carbon. This would become a more
sustainable alternative to current practices of cellulose production by
eliminating the cost and energy required for forest management, cellulose
extraction, and cellulose purification. Most importantly, it eliminates the use
of oil in the production of carbon fibers.

In this work,
we present the initial characterization of the response of G. xylinus
to electrical stimuli of varying frequencies as well as the protocol
developed to convert bacterial cellulose into carbon.  The dielectrophoretic response
was characterized using AC signals of 1, 5, 10, 15, and 20MHz frequencies at a
constant voltage of 20 V_pp. The results indicate a positive DEP
response across the spectrum of 1-20MHz with the highest trapping at a
frequency in the range of 15-20 MHz (figure 1). Additional work focused on the
carbonization of bacterial cellulose nanofibers. Amorphous carbon was
successfully achieved (figure 3) through heat treatment of bacterial cellulose to
900 C in a nitrogen atmosphere following a 5 C/min heating ramp. A dwell time
of 30 minutes at a temperature of 300 C was included in the heat treatment to
facilitate the release of oxygen from the sample to prevent burning at higher
temperatures. Such step is also necessary because the removal of the hydroxyl
groups stabilizes the carbon polymer by producing conjugated double bonds, forming
an aromatic structure [2]. An optimal heating rate was determined to be 5 C/min
to achieve high carbon yield without making the process prohibitively long.  Although
we observed cellulose to carbonize at around 400 C, 900 C was used as the
maximum temperature to ensure a high degree of carbonization [3].

Ongoing work is on characterizing the fiber
properties and dimensions depending on the suspending media and its flow rate
over the cells. The goal is to understand how the conditions in the
microfluidic platform lead to the tailoring of the fiber properties and a
maximized throughput.

Figure
1:
Characterizing the response of G. xylinus to Carbon DEP

Figure
2:
Carbonized Cellulose Nanofibers

References

1. Huang,
Y., Zhu, C., Yang, J., Nie, Y., Chen, C., & Sun, D. (2014). Recent advances
in bacterial cellulose. Cellulose, 21(1), 1-30.  

2.
McGrath, T. E., Chan, W. G., & Hajaligol, M. R. (2003). Low temperature
mechanism for the formation of polycyclic aromatic hydrocarbons from the
pyrolysis of cellulose. Journal of Analytical and Applied Pyrolysis, 66(1),
51-70.

3.
Rhim, Y. R., Zhang, D., Rooney, M., Nagle, D. C., Fairbrother, D. H., Herman,
C., & Drewry, D. G. (2010). Changes in the thermophysical properties of
microcrystalline cellulose as function of carbonization temperature. Carbon,
48(1), 31-40.