Cellulose and Chitin as Nanoscopic Biomaterials - The Nanoscience and Technology of Renewable Biomaterials - page 212

Compared to the cellulose whiskers obtained from other sources like ramie (16), cotton
(16), filter paper (17), or bleached kraft wood pulp (18), the microfibril dimensions for
particles isolated from bagasse appeared to be less uniform. The distribution of the
particle lengths for the cellulose whiskers has also been reported (15).
There have been some recent reports on the crystal morphology of cellulose using
AFM. Sugiyama and coworkers have used it to study the crystalline order in the bulk as
well as on the surface for microcrystalline cellulose isolated from Valonia ventricosa (19).
Images generated from our studies using AFM illustrated the fiber bundle morphology
in cellulose microfibers (MFs) isolated from bagasse (20). In Figure 8.3, we see whole
microfibrillar bundles as well as individual nanofibers (14).
In this figure, the left-hand image is a height image that represents surface topog-
raphy, while the right-hand image is a phase image whose contrast differentiates soft
(amorphous) and hard (crystalline) polymer segments. Both height and phase images are
recorded. These images agree well with the scanning electron micrographs. Increased
magnification of microfibrillar bundles reveals nanometer-scale (30 nm) structures as
shown in Figure 8.4.
These dimensions are comparable to those proposed by Hess et al ., for their schematic
representation of cellulose fiber structure (20). The banding apparent in these images
(see Figure 8.5) is consistent with the density fluctuations in the Hess model for the
microfibrillar assembly.
The presence of periods from 60 to 100 nm is representative of crystalline (bright
regions) and amorphous (dark) regions in the direction of the fiber axis. For semicrys-
talline polymers, lighter areas in phase images have been interpreted as crystalline

0 10.0 µ m 0 10.0 µ m

Data type
2 range

Height
400 nm

Data type
2 range

Phase
30.0 de

Figure 8.3 AFM images showing the fiber bundle morphology in cellulose isolated from
bagasse.Reprintedfrom(14).Copyright(2008),withpermissionfromElsevier.