FIGURE 3 The microscope images of (a) SCG,(b) NSCG , and (c) ASCG; The distribution map of(d) SCG, (e) NSCG, and (f) ASCG
To observe the influence of the atmosphere on the functional groups in
SCG, we obtained the FTIR spectra of SCG samples, as shown in Figure 4
(a). 3600-3100 cm-1 is ascribed to the vibration peak
of the O-H group. 3000-2700 cm-1 is attributed to the
tensile vibration region of C-H. The range of oxygen-containing
functional groups is between 1800 and 900 cm-1, such
as carbonyl group, carboxyl group, an ether bond, etc. (Silverstein and
Bassler, 1962). The effect of heat treatment on the functional groups of
SCG is insignificant. However, the peak intensity of ASCG diminished
significantly, because heat treatment reduced the content of O-H groups
and other oxygen-containing functional groups (Hussin et al., 2018).
The bar chart of SCG residual oil content and SCG relative weight loss
rate is shown in Figure 4 (b). The residual oil content of the SCG used
in this experiment is about 14%, and that of NSCG is about 13%, with
little change, but the ASCG is close to 10%. The results showed that
air atmosphere heat treatment was more beneficial to the oxidative
decomposition of oil in SCG. In terms of relative weight loss, ASCG is
twice that of NSCG. The cause is the evaporation of oil and other
ingredients.
The results of the water contact angle of the three SCG samples are
shown in Figure 4 (c). The water contact angle of SCG is 93.86°,
indicating that SCG showed weak hydrophobicity. The water contact angles
of NSCG and ASCG are 100.39° and 103.44°, respectively. The
hydrophobicity of SCG is enhanced, especially ASCG. The O/C ratio of SCG
decreased, resulting in enhanced hydrophobicity (van der Stelt et al.,
2011).