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and foldable films for display applications.
22
Although these
NFC materials have good mechanical properties, the full
mechanical potential of NFC was not fully achieved because the
orientation distribution of NFC was random-in-the-plane or
random-in-space.
Several efforts to orient cellulose nanofibers and whiskers
have been presented. Orientation has been reported in
dispersions, films, and fibers. In a dispersion, cellulose
microcrystals undergo spontaneous parallel arrangements in
the form of a chiral nematic phase.
23
A magnetic
24
or electric
25
field can also orientate rodlike cellulose whiskers in the liquid
state, and subsequent drying gives oriented films. Films of
highly oriented cellulose whiskers have been reported by
Received: November 29, 2011
Accepted: January 18, 2012
Published: January 18, 2012rotation of a glass vial containing aqueous dispersion of
whiskers, followed by drying.
26
All-cellulose films (composite
films of cellulose I and II) were cold drawn in the wet state to
induce orientation in the drawing direction.
27
For fibers with
oriented cellulose, wet spinning, hot drawing and electro-
spinning have been used. Wet spinning has been used on wood
cellulose nanofiber and tunicate whisker dispersions using
acetone as a coagulation bath. The spinning rate and the nature
of the starting dispersion was found to give different fiber
structure (hollow or porous fibers).
28
Hot-drawing in the
presence of a polymer matrix was used to obtain fibers with
cellulose whiskers in a PVA matrix where both the PVA matrix
and the whiskers showed a high degree of orientation.
29
Electrospinning also gives fibers with oriented whiskers in a
polymer matrix. The electrospun fibers can be randomly
assembled into a porous membrane, or aligned with a drum
collector.
30
The starting point of the present study is NFC nanopaper,
and this is a web-like network of cellulose nanofibrils.
5,12
The
NFC orientation distribution is random-in-the-plane. Interest-
ing properties include optical transparency,
31
smoothness,
12
low coefficient of thermal expansion,
31
good mechanical
properties,
5,12
and possibilities for functionalization.
21,32
The
nanopaper can be prepared by a water-based papermaking-like
filtration procedure,
5,12
and therefore offers solvent-free
preparation compared with regenerated cellulose films.
Furthermore, the nanopaper consists of cellulose I type fibrils
with better mechanical properties compared to cellulose II.
33
Suggested applications for NFC nanopaper includes films for
packaging applications,
5,6
electronic display application22
or as a
substrate for nanocomposites preparation (e.g., by impregna-
tion).
34
In this later application, an advantage would be to have
orientation of NFC so that further tailoring of the mechanical
properties becomes possible. For instance, it would be possible
to prepare laminates based on oriented film “plies” stacked with
varying orientation angle so that mechanical properties in
different directions can be tailored.
Cold drawing has already been used for preparation of all-
cellulose films with preferred orientation.
27
The preparation
steps of oriented all-cellulose films include partial dissolution of
MCC in LiCl-DMAc solvent, gelation, washing, drying of the
films, wetting of the dried films, stretching (cold drawing) of
the wet films, and finally drying the films in stretched
conditions. The drawn all-cellulose films presented excellent