3.2 Characterization of SCG
The influence of the heat treatment atmosphere on the color and
microstructure of SCG was investigated. The digital images of SCG, NSCG,
and ASCG are shown in Figure 2 (a-c). The colors of the SCG, NSCG, and
ASCG are light brown, dark brown, and light black, respectively. The
blackening degree of the ASCG is darker than that of the NSCG. The color
shifts indicate that SCG will be carbonized to some degree at the same
temperature, regardless of the atmosphere. In addition, the SEM images
corresponding to the three samples are shown in Figure 2 (d-f). It can
be found that they are agglomerate. But after heat treatment, the
surface of particles becomes fluffy and the adhesion degree of particles
decreases markedly. It is the result of partial volatilization of small
molecular weight materials and low molecular weight hemicellulose (van
der Stelt et al., 2011).