Civil Engineering Reference
In-Depth Information
with opposite handedness allows for the conservation of the rotation since the rotation
in one helix cancels the rotation in the other.
Another mathematical model that describes the formation of perversions in helices
can be found in literature [97-99] and models the transition from a twisted rod to a
helix by making some approximations; the rod must be elastic, slender and have intrin-
sic curvature and torsion. h e use of this model allowed the calculation [103] of the
applied tension on a APC suspended electrospun i ber and the critical tension, below
which the i ber starts to twist, by counting the number of turns present in a suspended
i ber from pictures obtained by SEM observation.
h e explanation of the cause of the twisting of electrospun APC i bers from the liq-
uid crystal phase and why these i bers coil into helices, and where the intrinsic curva-
ture came from, was provided in a more recent paper [107].
8.3
Conclusions
Cellulose is a fascinating biopolymer that has always been used in the production of
textile i bers. Due to environmental concerns intense research has been conducted in
the past decades in order to substitute traditional carbon or glass i bers used in the
production of composites with eco-friendly cellulose i bers. h e research in cellulose-
based biocomposites is now focused on the concept of self-reinforced nanocomposites.
In this sense all-cellulose composites have been investigated showing mechanical prop-
erties comparable or even better than those of traditional composites. Cellulose and its
derivatives may also show liquid crystalline mesophases, which can be used to produce
new and biomimetic materials with distinctive mechanical and optical properties. Most
likely, enhanced mechanical properties will be obtained in all-cellulose nanocompos-
ites by taking full advantage of the orientational order, when both the matrix and the
i bers are in a liquid crystalline state.
Acknowledgements
h is work has been i nanced by the Portuguese Science and Technology Foundation
(FCT-MEC) through projects PTDC/CTM-POL/1484/2012 and PEst-C/ CTM/LA
0025/2013-2014. S. N. Fernandes also acknowledge FCT for grant SFRH/BPD/78430/
2011. h e authors would like to acknowledge Keiran Fleming, Derek G. Gray, and
Stephen Matthews, in “Cellulose Crystallites”, Chem. Eur. J., and WILEY-VCH Verlag
GmbH, Weinheim, Fed. Rep. of Germany for the kind permission to use Figure 8.1.
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