AFM images of the NCC samples prepared at different hydrolysis
conditions are shown in Fig. 1. It was found that the NCC
samples were rod-like crystals, with cross-sections in nanometer
range. The mean diameter was comparable to those reported by
Hafraoui et al. [26], who studied the shape and size distribution
of crystalline nanoparticles prepared by acid hydrolysis of native
cellulose. When hydrolysis time was extended from 25 min to
30 min, the mean diameter decreased from 22.85 nm to 19.43 nm.
It was also noticed that, when the temperature was increased from
45 ◦C to 55 ◦C, the mean diameter of the NCC samples decreased
slightly. Harsher treatment, such as longer time and higher temperature,
could destroy not only the amorphous area but also
the crystalline zones of the fibrils, which resulted in narrower
nanoparticles.