Civil Engineering Reference
In-Depth Information
causes the cellulose production to become redundant, as it is believed the purpose of
the cellulose pellicle is to anchor the bacterial cells to the surface in order to obtain
sui cient oxygenation.
4.2.2.2
Properties and Methods of Characterization
h ere are a number of common techniques that researchers use to characterize bacterial
cellulose. Whilst this is by no means a comprehensive list, these techniques do provide
a good indication of alterations that may have occurred during the cultivation of the
bacteria, as cellulose polymerization and crystallization are closely coupled processes,
and changes to the cultivation conditions can change the structure and morphology of
the resulting cellulose [35].
Scanning electron microscopy (SEM) is a common method used to observe both
the surface and cross-section view of bacterial cellulose. It shows a network of random,
interwoven, nanosized i brils. TEM is less commonly used for this purpose. Figure 4.4
demonstrates the interwoven i brils as shown by SEM and the microi bril extruding
from the cell membrane by TEM [36].
Nuclear magnetic resonance (NMR) and Fourier transform-infra red (FTIR) spec-
troscopy have been common techniques used to coni rm that the material produced
in bacterial culture is bacterial cellulose and to determine the I
α
content of the sample.
In addition, Yamamoto
et al.
[37] used NMR results to determine that the cellulose I
α
content be calculated by the relationship between the FTIR absorbance at peaks 750
and 710 cm
-1
. h e stretching of peaks and additional peaks can indicate the presence of
changes or additional materials within the cellulose.
X-ray dif ractometry (XRD) of bacterial cellulose samples allows for the calculation
of crystallinity and crystallite sizes of the resulting cellulose, however various research-
ers use dif erent peaks for these calculations [34, 37, 38] which can result in large dif er-
ences between the calculation of these values. Crystallinity has also been reported to be
determined by Fourier transform Raman spectroscopy [39]. Based on the variation of
values obtained from dif erent methods, care should be taken when comparing crystal-
linity and crystallite sizes between dif erent reports in the literature.
Some researchers complete additional characterizations such as water holding capac-
ity, and there are also reports in the literature of mechanical tests done on bacterial
Figure 4.4.
SEM (a) and TEM (b) of bacterial cellulose structure. Reproduced from [36] with permission
from Springer.
