A semidilute cellulose nanocrystal suspension was tested for pressure, volume, temperature dependencies of its viscosity and density. The compression of a 2.0 wt % cellulose nanocrystal suspension under 5.0 MPa at room temperature resulted in morphological changes from istotropic to nematic form. However, at high temperature, high-pressure treatment caused desulfation and gelation. Those results have significant applications, not only as additives in drilling and fracturing fluids but also for the preparation of hydrogels.