Cellulose is a naturally occurring and highly crystalline
polysaccharide with fibrous morphologies mostly present
as one of the major plant components, and is expected to be
used as the most abundant and renewable carbon resource
on earth for establishment of sustainable society [1, 2].
Plant cellulose microfibrils have lengths and widths of
greater than 1 lm and approximately 4 nm, respectively,
and thus have high aspect ratios. Moreover, cellulose
microfibrils have high elastic moduli (*140 GPa) due to
high crystallinities [3]. These unique properties provide
potential applications of cellulose microfibrils as bio-based
nanomaterials in various high-tech and commodity fields.
In this context, nanofibrillated celluloses and nanocrystalline
cellulose whiskers have recently been attracted much
attention because of their promising properties as finely
molecular-assembled, highly crystalline and bio-based
nanomaterials [4–7]. Nanofibrillated celluloses are prepared
by mechanical disintegration of native cellulose fibers and
pre-treated native celluloses in water, and generally have
fibril lengths[200 nm [6, 7]. On the other hand, nanocrystalline
cellulose whiskers are prepared by acid hydrolysis
of native celluloses with, for instance, 64 % sulfuric
acid and the successive mechanical disintegration of the
water-insoluble hydrolyzed products in water, and have
spindle-like morphologies and lengths100 nm [4, 6].