3.1 Basis of the heat treatment process
The TG curves of SCG in different atmospheres show in Figure 1. The mass loss of the two atmospheres is roughly the same at 310 °C. There have 5% of the mass loss in the first stage occurred at 200 °C, probably due to the volatilization of free and bound water (Zarrinbakhsh et al., 2016). The most significant mass loss begins at 240 ℃. It is caused by the breakdown of small molecular weight substances and hemicellulose. After 310 ℃, ASCG is oxidized and decomposed. To avoid excessive weight loss of SCG, a heat treatment temperature of 240 °C was selected. Lignin and cellulose decompose at lower temperatures.