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).