NCC is formed by rigid rod-like particles with widths and lengths
of 5–70 nm and between 100 nm and several micrometres respectively.
The particles are 100% cellulose and highly crystalline,
between 54 and 88% (Moon et al., 2011). The aspect ratio, defined
as the length to diameter ratio, spans a broad range. The variety
of dimensions, morphologies, degree of crystallinity depends
on the source of cellulosic material and conditions under which
preparation is carried out (Habibi et al., 2010) as well as on the
experimental technique used, as shown in Table 4. Moreover, as
the cleaving of cellulose chains occurred randomly during the acid
hydrolysis process, the dimensions of NCC are not uniform. It was
reported that NCC derived from tunicate and bacterial cellulose is
generally larger in dimensions compared to those obtained from
wood and cotton (see Table 4). This is because tunicate and bacterial
cellulose are highly crystalline hence there are lower fractions
of amorphous domains that need to be cleaved resulting in the
production of larger nanocrystals. NCC from wood is 3–5 nm in
width and 100–200 nm in length, and that from wheat straw – an
interesting residual lignocellulosic biomass – seems similar.