Civil Engineering Reference
In-Depth Information
and scalable for drying of aqueous suspension of CNCs and creates free-l owing and
l our-like powder having a range of particles from nano-to micron-scale which are con-
trollable [126, 127]. Morphological investigations of CNCs by using air-drying, freeze-
drying, and spray-drying can be seen in Figure 15.10.
h e full redispersion of CNCs is also a major challenge. According to Beck
et al.
,
if dried H-CNCs have residual moisture content above the threshold value of 4% by
weight, then they can be redispersed in water without any chemical modii cation or
use of additives. h erefore, a lightweight and redispersible form of H-CNCs can be
produced by controlling the degree of dryness. Below this value of moisture content,
H-CNCs will be non-dispersible. However, if a minimum of 94% of the H
+
counterion is
exchanged with a neutral M
+
form (such as Na
+
), then the neutral salt form (Na-CNCs)
of dried CNCs can easily be dispersed in water, even when fully dried [126], as shown
in Figure 15.11.
Figure 15.10
(a) Air-dried NCC i lm showing its iridescent properties when viewed normal to the
surface (let ) and at an oblique angle to the surface (right). Scale bar = 2 cm. (b) Flakes of freeze-dried
NCC. Scale bar = 1 cm. (c) Spray-dried NCC powder. Scale bar = 1 cm. ESEM images: (d) Fracture edge
of an air-dried NCC i lm with visible NCC layers. Scale bar = 20 μm. (e) Edge of freeze-dried NCC l ake
(arrows indicate individual nanocrystals). Scale bar = 500 nm. (f ) Granules of spray-dried NCC. Scale
bar = 10 μm [126].
