3.2. Morphology of the chemical-purified cellulose fibers and
cellulose nanofibers
Fig. 3 shows the FE-SEM images of the chemical-purified cellulose
fibers. After chemical pretreatment, the cellulose fibers were
separated into individual micro-sized fibers. In fact, these microsized
fibers were reportedly composed of strong hydrogen bonding
nanofibers, and individualized nanofiber bundles with a width of
10–30nm can be seen on the surface of the micro-sized cellulose
fiber (Fig. 3c). However, the samples still maintained the initial cell
shape (Fig. 3b). After ultrasonic treatment, individual nanofibers
can be obtained.
Fig. 4 compares the TEM images of the isolated nanofibers
obtained after a 30min high-intensity ultrasonication treatment at
various output powers. The diameter distributions of the nanofibers
were analyzed; the result is also plotted in Fig. 4.
When the output power of ultrasonication was conducted at
400 W, large aggregates consisting of wire-like cellulose fibers
with nanoscale widths were frequently observed; a number of
branches of smaller bundles or partly individualized nanofibers
were attached to the large aggregates as well. Although nearly
62% of the nanofibers were shorter than 20 nm, the diameter distribution
of the cellulose fibers exhibited a wide array of sizes,
ranging from several nanometers to several hundred nanometers.
The number of individualized cellulose nanofibers increased for