Civil Engineering Reference
In-Depth Information
4.4.2
Renewable Matrix Polymers
h ere are a large number of polymers that could potentially be used as a matrix mate-
rial in combination with bacterial cellulose as a i ller material. Bacterial cellulose is
predicted to have a naturally high ai nity with hydrophilic materials, as it too is hydro-
philic. h erefore, potential matrix materials include materials such as PLA. PLA is a
biodegradable thermoplastic polyester produced from renewable sources. It has previ-
ously been used in combination with cellulose nanoi bers to improve the mechanical
properties of the PLA [180]. Materials such as PVA and starch from a variety of sources
are also biodegradable materials that could act as matrices for reinforcement. In addi-
tion, are hydrophobic biodegradable materials that could potentially be improved in
terms of their mechanical properties by being combined with a second phase in a com-
posite. Of the hydrophobic materials, the bioplastic PHB has been proposed as having
the potential to replace traditional plastics [22], as it has similar properties to polypro-
pylene [181, 182]. PHB is probably the most well known of the PHAs, a family of homo-
or hetero-polyesters produced by bacterial species that accumulate them intracellularly
and use them for energy. h ey all consist of a single chain with a 3-carbon backbone,
but dif er with side chains at the 3 position. It is this side chain that determines the
specii c PHA. For example, PHB has a methyl group at the 3 position [183]. It has been
hypothesized that an appropriate i ller material could improve the properties of materi-
als such as PHB [184].
h e ability to tailor design bacterial cellulose with specii c properties provides the
possibility that there may be a range of biodegradable matrices that could use this cel-
lulose as the reinforcement material. Determining appropriate
in-situ
or post modi-
i cations of bacterial cellulose, as well as the method of creating the composite and
potential matrices is a complex process that requires further investigation. Attention
should focus on biodegradable matrices and methods that can produce composites on
a large scale, to develop useful materials.
4.4.3
Bacterial Cellulose Composites
Bacterial cellulose has been used as a material in combination with many others to
develop composites. It has been used with materials such as unsaturated polyester
[185], the conducting polymer polyaniline [158-162, 186], as well as various acrylic
and phenolic resins [178, 187-189]. It has also been used with several biodegradable
materials such as cellulose acetate butyrate (CAB) [146, 190], PLA [167, 174, 191, 192],
PHB [193-195], PVA [196, 197], and thermoplastic starch [198, 199], to produce com-
pletely biodegradable composites. h ough renewable and biodegradable composites
are the focus of this review, techniques and resulting composites from non-renewable
sources are also mentioned.
4.4.3.1
Impregnating Bacterial Cellulose
Several researchers have used an impregnation method to develop composites with
bacterial cellulose, similar to the modii cation method described previously, except
that the material used forms a sheet rather than individual particles upon drying. h e
soaking of the cellulose may occur from dry, or never-dried i lms, or i lms that have
