3 research outputs found
Understanding the Dispersive Action of Nanocellulose for Carbon Nanomaterials
This work aims at understanding the
excellent ability of nanocelluloses to disperse carbon nanomaterials
(CNs) in aqueous media to form long-term stable colloidal dispersions
without the need for chemical functionalization of the CNs or the
use of surfactant. These dispersions are useful for composites with
high CN content when seeking water-based, efficient, and green pathways
for their preparation. To establish a comprehensive understanding
of such dispersion mechanism, colloidal characterization of the dispersions
has been combined with surface adhesion measurements using colloidal
probe atomic force microscopy (AFM) in aqueous media. AFM results
based on model surfaces of graphene and nanocellulose further suggest
that there is an association between the nanocellulose and the CN.
This association is caused by fluctuations of the counterions on the
surface of the nanocellulose inducing dipoles in the sp<sup>2</sup> carbon lattice surface of the CNs. Furthermore, the charges on the
nanocellulose will induce an electrostatic stabilization of the nanocellulose–CN
complexes that prevents aggregation. On the basis of this understanding,
nanocelluloses with high surface charge density were used to disperse
and stabilize carbon nanotubes (CNTs) and reduced graphene oxide
particles in water, so that further increases in the dispersion limit
of CNTs could be obtained. The dispersion limit reached the value
of 75 wt % CNTs and resulted in high electrical conductivity (515
S/cm) and high modulus (14 GPa) of the CNT composite nanopapers
Nanostructured Wood Hybrids for Fire-Retardancy Prepared by Clay Impregnation into the Cell Wall
Eco-friendly
materials need “green” fire-retardancy treatments, which
offer opportunity for new wood nanotechnologies. Balsa wood (Ochroma
pyramidale) was delignified to form a hierarchically
structured and nanoporous scaffold mainly composed of cellulose nanofibrils.
This nanocellulosic wood scaffold was impregnated with colloidal montmorillonite
clay to form a nanostructured wood hybrid with high flame-retardancy.
The nanoporous scaffold was characterized by scanning electron microscopy
and gas adsorption. Flame-retardancy was evaluated by cone calorimetry,
whereas thermal and thermo-oxidative stabilities were assessed by
thermogravimetry. The location of well-distributed clay nanoplatelets
inside the cell walls was confirmed by energy-dispersive X-ray analysis.
This unique nanostructure dramatically increased the thermal stability
because of thermal insulation, oxygen depletion, and catalytic charring
effects. A coherent organic/inorganic charred residue was formed during
combustion, leading to a strongly reduced heat release rate peak and
reduced smoke generation
Highly Conducting, Strong Nanocomposites Based on Nanocellulose-Assisted Aqueous Dispersions of Single-Wall Carbon Nanotubes
It is challenging to obtain high-quality dispersions of single-wall nanotubes (SWNTs) in composite matrix materials, in order to reach the full potential of mechanical and electronic properties. The most widely used matrix materials are polymers, and the route to achieving high quality dispersions of SWNT is mainly chemical functionalization of the SWNT. This leads to increased cost, a loss of strength and lower conductivity. In addition full potential of colloidal self-assembly cannot be fully exploited in a polymer matrix. This may limit the possibilities for assembly of highly ordered structural nanocomposites. Here we show that nanofibrillated cellulose (NFC) can act as an excellent aqueous dispersion agent for as-prepared SWNTs, making possible low-cost exfoliation and purification of SWNTs with dispersion limits exceeding 40 wt %. The NFC:SWNT dispersion may also offer a cheap and sustainable alternative for molecular self-assembly of advanced composites. We demonstrate semitransparent conductive films, aerogels and anisotropic microscale fibers with nanoscale composite structure. The NFC:SWNT nanopaper shows increased strength at 3 wt % SWNT, reaching a modulus of 13.3 GPa, and a strength of 307 MPa. The anisotropic microfiber composites have maximum conductivities above 200 S cm<sup>–1</sup> and current densities reaching 1400 A cm<sup>–2</sup>