Civil Engineering Reference
In-Depth Information
Figure 4.9
Starch/bacterial cellulose
in-situ
composites, Grande
et al.
2009 [221]. Some bacterial
cellulose i bers can be seen amongst starch as shown by arrows. Reprinted with permission from Elsevier.
composites reported contained only small amounts of the additive, and only resulted in
small changes to the cellulose properties.
h ere have been others, however, who have reported much higher concentrations of
the host polymer in the composite. Brown and Laborie [220] added PEO to the culture
medium and developed several nanocomposites with dif erent ratios, ranging from 15
to 59% bacterial cellulose, demonstrating dif erent compositions and morphologies. In
addition, they determined that increased bacterial cellulose contents resulted in smaller
cellulose i bers and an aggregation of these i bers, although at lower cellulose contents
the i bers could be i nely dispersed. h ese researchers did not attempt to remove the
bacterial cells from the composite for fear that PEO would be lost in the washing pro-
cess, and they found that the cell debris impacted the properties of the composite. As
in-situ
composites are created directly from the bacterial culture, resulting composites
may be contaminated with cell debris. h e question of whether or not the cell debris
needs to be removed is something that requires further investigation with a wider range
of materials. Grande
et al.
[221] developed a method to create
in-situ
bacterial cellulose
composites by including starch in the culture medium at a concentration of 2%. h e
starch was partially gelatinized during the autoclaving of the media, and the bacterial
cellulose/starch gels that were subsequently produced were then hot pressed in order
to encourage further dif usion of the starch into the cellulose network. SEM images of
these composites showed good coverage of the cellulose with starch; some i brils were
still visible (see Figure 4.9), however the bacterial cellulose was largely dispersed and
the nanocomposites had good mechanical properties.
Due to the biological nature of bacterial cellulose,
in-situ
methods involving the
inclusion a polymer in the culture medium for cellulose to combine the materials pro-
vides an alternative method for creating composites. It is possible that composites could
be made simply by the inclusion of the host polymer in the medium, however the devel-
opment of subsequent treatments, for example the hot pressing of the starch/cellulose
i lms described above, could improve the contact and interactions between the two
materials. Identifying materials to be used in composites with bacterial cellulose in this
way could provide improvements into the development of these types of composites.
4.4.3.5
Bacterial Cellulose Composites by Other Methods
Various impregnation methods have been used to develop composites with bacterial
cellulose, with increasing numbers of solution blends and melt blends reported, how-
ever there are also reports of composites published that have used entirely dif erent
methods. Quero
et al.
[191] compressed strips of bacterial cellulose between two strips
of PLA i lms. h is work found a dif erence between composites with bacterial cellulose
