*3.2. Mechanical Properties of Aerogel*

The typical compression stress–strain curve of CA with different cellulose content is shown in Figure 3.

**Figure 3.** Typical compression stress–strain curves of cellulose aerogel (CA) with various cellulose concentration.

Figure 3 could be explained by two stress regions with increasing cellulose content. The first region appeared before 60% strain and can be characterized by slowly increasing stress, while the second region appeared at above 60% strain with rapidly increasing stress. The stress of CA obtained from 1.5, 2.0, and 2.5 wt.% of cellulose concentration at 60% strain was 1.37 ± 0.01; 1.55 ± 0.01, and 1.83 ± 0.02 MPa, respectively. At 80% strain, the stress of corresponding cellulose aerogels increased to 2.99 ± 0.02, 3.41 ± 0.01, and 4.01 ± 0.02 MPa, respectively. These results mean that the stress increased with increasing cellulose concentration as a result of higher crosslinking density. In addition, the slope of stress–strain curves was also increased with increasing cellulose content in the CA. The slope of stress–strain corresponded to the compressive modulus and the internal structure of aerogel. The high crosslinking density also was considered as a reason of increment of the compressive modulus above.
