Civil Engineering Reference
In-Depth Information
h ere has been a report of solution blending to combine CAB and bacterial cellulose
nanocrystals [146]. As discussed above, bacterial cellulose was treated with sulfuric
acid to obtain nanocrystals, and was subsequently trimethylsilylated. h ese chemically
modii ed nanocrystals were then dispersed in acetone, and the acetone was used to dis-
solve CAB and was cast to form i lms with up to 10% cellulose. h e melting tempera-
tures of the composites showed a change, increasing with increasing concentrations
of silylated cellulose, however this change was not seen with native nanocrystals. h e
modulus of the composites showed increasing values with increasing cellulose contents
with the native crystals over most of the temperature range. h e researchers concluded
that the unmodii ed cellulose crystals had better reinforcement characteristics than the
chemically modii ed cellulose, however the improved properties may have been due to
increased native cellulose content in the composites over the silylated cellulose, as some
of the weight of the silylated cellulose was due to the silyl groups.
Bacterial cellulose i bers have been dispersed in several ways to develop PVA com-
posites. Bacterial cellulose has been homogenized [197, 205], milled to powder [206]
and dispersed by vigorous stirring [143, 207] prior to mixing with PVA solution.
Homogenization of bacterial cellulose has also been used to obtain composites with
arabinoxylan [208] and pullulan [209], as well as thermoplastic starch [199]. h ese
composites were cast and dried at room temperature, 30
C, respectively.
Bacterial cellulose mixed with water and NaOH before sonication, freezing, thawing,
stirring and centrifuging was added to aqueous graphene oxide to develop graphene/
bacterial cellulose composites [210]. h ese composites also used various combinations
of sonication, homogenization and stirring to achieve i ber dispersion. PHBV has been
used as a matrix material (with dif ering valerate contents) to develop solution blends
using bacterial cellulose nanowhiskers as the reinforcing phase [202]. h e bacterial
cellulose nanowhiskers were subjected to a solvent exchange process in chloroform,
before being homogenized for two minutes, and then blended with PHBV, cast onto
petri dishes and dried at 60
°
C and 60
°
C under vacuum. Good dispersion of the nanowhiskers
was seen at 1%, however some aggregation was observed at 3% [202]. Despite the good
dispersion, mechanical properties did not display any statistical signii cance from the
neat materials in tensile strength and modulus. Many of the composites described here
showed good mechanical properties, however some aggregation of cellulose i bers was
observed. Developing a method to maintain the desirable traits of bacterial cellulose
while, at the same time, obtaining even dispersion and distribution of cellulose in solu-
tion would allow a simple method to combine materials with controlled concentrations
of cellulose.
°
4.4.3.3
Electrospinning and Melt Blending
While many researchers use bacterial cellulose in its native form to create polymers,
and some treat the bacterial cellulose by homogenization or hydrolyzation prior to cast-
ing, there is very little in the literature about the dissolution of bacterial cellulose as
part of a method to create composites. One method that has used the dissolution of
bacterial cellulose is electrospinning. Chen
et al.
[148] used the ionic liquid 1-allyl-
3-methylimidazolium chloride to dissolve freeze-dried bacterial cellulose pieces at
70°C while stirring. DMSO was added to the solution to adjust the viscosity at room
