Mechanical properties of carboxymethyl cellulose aerogels and cryogels

Lightweight and highly porous carboxymethyl cellulose (CMC) aerogels were prepared from CMC solutions via non-solvent induced phase separation, followed by supercritical CO₂ drying. Direct freeze-drying of CMC solutions was used to obtain “cryogels” for comparative analysis. The influence of CMC concentration and of drying method on the morphology, density, porosity and mechanical response of CMC aerogels and cryogels under uniaxial compression were evaluated. Two methods were used: direct data collection from the machine sensors and the digital image correlation (DIC) technique. It was demonstrated that DIC method is more precise; video-monitoring of the changes in sample shape and dimensions was also performed. Nominal stress–strain dependences were constructed, and compressive modulus, yield stress, absorbed energy and sample volume evolution under compression were analyzed as a function of density and material morphology. The elastic recovery of cryogels is slightly higher than that of aerogels at the similar density. The “equivalent” Poisson’s ratio (at 50% strain) was nearly zero for cryogels, while for aerogels it was non-zero and decreased with increasing density. The difference in the mechanical response of aerogels vs cryogels was attributed to their different morphology.