Civil Engineering Reference
In-Depth Information
Figure 4.7
SEM images of bacterial cellulose grown with PHB in the media. Reproduced from [114]
with permission from Elsevier.
irregular clumps [81] . h is led to lower crystallinity and smaller crystallite size. Zhou
et al.
[81] also demonstrated that hydrogen bonding interactions occurred between
the cellulose and the sodium alginate. Tokoh
et al.
[118] showed that the presence of
acetyl glucomannan in the medium changed the crystal structure of cellulose with
an increased cellulose I
β
fraction and caused the cellulose to form as loose bundles of
microi brils, with decreased crystallite size. Polyethylene glycol 400 and
β
-cyclodextrin
in the growth medium of
G. xylinus
resulted in bacterial cellulose with increased pores.
However, the addition of polyethylene glycol 4000 was shown to decrease pore size and
decrease degree of polymerization [119]. Acid-treated multi-walled carbon nanotubes
(MWCNT) were added to the culture medium used to grow
G. xylinus
under static
conditions. h e cellulose produced by the bacteria under these conditions had altered
crystal structure, cellulose I
α
content, crystallinity index and crystallite size [120]. When
glucose-phosphate was added to the culture medium, either as the sole carbon source
or in conjunction with glucose, phosphate-containing cellulose was produced [121].
h is cellulose can be used as an environmentally friendly paper additive.
In-situ
modii cations that occur in cellulose from the inclusion of additives can
directly or indirectly impact the structure of cellulose and can be used to target specii c
properties or characteristics. It is also possible for additives in the media to be included
in the bacterial cellulose as it grows. If the additive is incorporated into the cellulose,
a composite material can be produced as a result of this
in-situ
modii cation. Ruka
et
al.
[114] have investigated the
in-situ
modii cation of cellulose using poly-3-hydroxy-
butyrate and have shown the dispersion of PHB throughout the cellulose (Figure 4.7).
h is method of creating composites is discussed further below.
4.3.3
Post Modii cations
Similar to
in-situ
modii cations, post modii cations (changes to cellulose at er growth)
could provide the opportunity to tailor-design the material in order to achieve specii c
properties, which is particularly relevant if cellulose is to be included in blends and
composites with other materials. h ese changes may be chemical or physical. For exam-
ple, chemical changes may be necessary as cellulose is a hydrophilic molecule, which is
a problem for cellulose i bers if they are to be used as reinforcement in plastics [122].
