Civil Engineering Reference
In-Depth Information
pore structures and tunnels within the BC membrane. It was demonstrated that strong
physical and chemical interaction exists between the BC nanoi brils and the particles of
GNP or MWCNT, revealing how the electrical conductivity of bacterial cellulose-based
composite membranes can be improved. Moreover, in Koga
et al.
[111] , ultrastrong,
transparent, conductive and printable nanocomposites were successfully prepared by
mixing single-walled carbon nanotubes (CNTs) with oxidized cellulose nanoi brils.
h e surface-anionic cellulose nanoi brils had reinforcing and nanodispersing ef ects
on the CNTs both in water used as the dispersed medium and in the dried composite
i lm, providing highly conductive and printable nanocomposites with a small amount
of CNTs. h ese systems are therefore now perceived as an ef ective l exible matrix that
can be used as an alternative to conventional polymers for various electrical materials.
A hydrophobic superabsorbent matrix was also produced through the use of cellulose-
i bril-based hydrogels. h ese showed elastic mechanical behavior in combination with
reversible electrical response under compression, allowing responsive conductivity and
pressure sensing for the hybrids. h e concept combines wide availability of nanocel-
lulosics and electrical functionality of carbon nanotubes synergistically. In Malho
et al.
[112], nanocomposites consisting of aligned assemblies of multilayered graphene and
nanoi brillated cellulose with excellent tensile mechanical properties without any sur-
face treatments were obtained by direct exfoliation of graphite within aqueous hydro-
gels of cellulose. h e interest for electrical properties originated studies over the strain
sensitivity of the conductivity properties of nanocellulose/carbon nanotubes compos-
ites [113] . A specii c type of nanopaper, including among other substrates also carbon
nanotubes, has also been proposed, aimed at conductive uses for very low voltage, typi-
cally in optoelectronics [114].
6.3.4
CNR and Biological Nanoreinforcements
With increased interest in alternatives to fossil fuels, there has been a signii cant move
towards the fabrication of functional materials based on i brillar materials that can be
extracted from renewable sources [115, 116]. In this regard, four compounds stand out:
(i) cellulose, the most abundant biopolymer present in the cell wall of green plants and
algae; (ii) chitin, the next most abundant biopolymer present in insects, crustaceans,
fungi, and diatoms; (iii) collagen, the most abundant protein in the animal kingdom
present in most vertebrates, particularly in tendons, bones, skin, corneas, and cartilage;
and (iv) silk, an old commodity protein used in textiles and medical sutures. As an
example, Butchosa
et al.
[117] implemented an environmentally friendly approach for
the production of nanocomposites with bactericidal activity, using bacterial cellulose
(BC) nanoi bers and chitin nanocrystals (ChNCs), showing that chitin nanoparticles
have great potential as substitutes for unfriendly antimicrobial compounds such as
heavy metal nanoparticles and synthetic polymers to introduce antibacterial proper-
ties to cellulosic materials (
Figure 6.2D
). In addition, an acidic cellulose/chitin hybrid
gel electrolyte is prepared from cellulose, chitin, binary ionic liquids, and an aqueous
H
2
SO
4
solution for an electric double-layer capacitor (EDLC) and the results indicate
that the acidic cellulose/chitin hybrid gel electrolyte has a practical applicability to an
advanced EDLC with excellent stability and working performance [118]. Cellulose/chi-
tin hybrid-type branched polysaccharides have been also synthesized through a series
