Civil Engineering Reference
In-Depth Information
determined that the electrospinning technique was particularly successful, resulting in
good dispersion of nanowhiskers up to 3%, with increases in the elastic modulus and
tensile strength from these conditions [217].
Melt blending was used to develop PLA/bacterial cellulose composites, where the
cellulose was disintegrated, and subject to solvent exchange before being chemically
modii ed by acetylation [167]. Melt blending was carried out at 190
C for 10 minutes at
100 rpm with the composites then injection moulded. Unmodii ed bacterial cellulose
i bers were found to agglomerate. Despite the high processing temperature of 190
°
C
used here, the acetylated cellulose composites demonstrated improved mechanical
properties, indicating that melt blending may be useful in developing fully biodegrad-
able composites.
h ese recent reports demonstrate that it may be possible to adapt a more traditional
method, such as melt compounding, to disperse bacterial cellulose and use this mate-
rial as a reinforcing phase in composites. h is type of technique can be easily upscaled
and may be adapted provide a method to produce bacterial cellulose composites for
commercial applications.
°
4.4.3.4
In-Situ Composites
h e inclusion of additives not specii cally required for cell growth or cellulose produc-
tion in the growth media can af ect the cellulose produced (see Section 4.3.2). We have
stated that some researchers observe a change in the structure, morphology and/or
properties of the resulting cellulose [76, 218], whereas others have determined that the
host polymer present in the culture medium can combine with the cellulose, creating
in-situ
composites [119, 219]. CMC and methylcellulose (MC) have been included as
additives in media for bacterial cellulose growth with dif ering results. Some authors
reported that these additives resulted in changes to the cellulose, including decrease
crystal size and crystallinity, with increased thermal stability and pore size [76], but did
not investigate the presence of the additives in the cellulose product, instead focusing
and reporting on the alterations to the cellulose. Others stated that when CMC and
MC were included in the media along with the growing cellulose, composite materials
were created, but the amount of the additive in these composites was not determined
[219]. When acid-treated MWCNTs were added to the culture medium, cellulose was
produced with altered structure, but it was also determined that the nanotubes became
interwoven within the cellulose i brils, ef ectively producing composites of these two
materials [120]. Weakened intermolecular hydrogen bonds also resulted as a result of
weaker bonds between the MWCNT and the cellulose, compared to bonds in the cel-
lulose alone. However, this paper did not report on the content of the MWCNT or cel-
lulose in the product, or the mechanical properties of the resulting membranes. PVA
was also added to the culture medium for bacterial cellulose, and the resultant cellulose
exhibited dif erent properties to neat cellulose, but no PVA was detected in the cel-
lulose at er the product was washed [219]. Gea
et al.
[196] created bacterial cellulose/
PVA nanocomposites by the inclusion of PVA in the culture media at dif erent concen-
trations, and they estimated that PVA was included in the composite, at a maximum
value of 1.3%. It is apparent that whilst
in-situ
bacterial cellulose composites can be
created by simply including an appropriate additive in the growth media, many of the
