Civil Engineering Reference
In-Depth Information
published. Schlut er
et al.
[140] used the ionic liquid 1-
N
-butyl-3-methylimidazolium
chloride to ei ciently dissolve bacterial cellulose before acetylation and carbanila-
tion by the addition of acetic anhydride and phenyl isocyanate, respectively, achiev-
ing extremely high degrees of substitution. h e ability to completely dissolve highly
polymerized bacterial cellulose presents the option to further (and homogeneously)
achieve chemical modii cations to this molecule, making it a more favorable biopoly-
mer for use as reinforcement in polymer matrices. However, while dissolution does
expose more surface and thus allow for higher degrees of substitution in these chemi-
cal reactions, the crystalline structure of bacterial cellulose is lost in the process [175],
thereby altering the cellulose and potentially af ecting the highly desirable properties
that makes this molecule so favorable for use as reinforcement. It will, therefore, be nec-
essary to determine if dissolution for chemical modii cation conveys a greater benei t,
or if surface modii cations provide sui cient alteration to bacterial cellulose to improve
its properties for further use in material science.
It is worth mentioning that bacterial cellulose has been modii ed for reasons other
than its use in composites. For example, bacterial cellulose has been modii ed by nitro-
gen-containing plasma in order to improve its cell ai nity, and thus increase its poten-
tial for use in biomedical applications [176]. h is opens the door, not only for other
uses for bacterial cellulose but also additional ways it can be modii ed.
4.4
Bacterial Cellulose Composites
4.4.1
Introduction
Composites can be entirely synthetic, a combination of synthetic and natural, or com-
pletely natural. As with most traditional synthetic polymer matrices, biopolymers could
also benei t from being used in conjunction with i bers to improve the mechanical prop-
erties of the matrix [11]. Desirable biocomposites could therefore benei t from being
created using a biodegradable polymer as the matrix material, and bioi bers as a rein-
forcing element [1]. While it is possible to combine synthetic and renewable technolo-
gies, such as composites with biodegradable cellulose i bers used as reinforcement in
polymers such as polyester, epoxy, amino and phenolic resins, these would not be fully
biodegradable because of the synthetic matrices [1, 177, 178]. h e use of biopolymers
currently has severe limitations with inferior properties and high production costs, but
should be completely biodegradable when used as both matrix and i ller. In addition
to traditional i ber micro-composites, nanocomposites are composites that have been
reinforced with nanosized particles [13]. Bacterial cellulose is a good candidate for
such reinforcement with its naturally produced nanosized i brils. Biocomposites can
be developed by various methods, and the methods by which the matrix and reinforce-
ment material are combined can strongly inl uence the properties of the resulting com-
posite. For example, extrusion and injection moulding are simple methods by which
composites can be produced, however processing parameters such as mixing time,
speed and temperature all have been found to alter tensile strength [179]. As the focus
of this review is bacterial cellulose, methods that have been used to create composites
that involve bacterial cellulose have been described in more detail in Section 4.4.3.
