Crystalline-to-amorphous transformation of cellulose in water, just like that for starch upon cooking called gelatinisation, is revealed at 320 °C and 25 MPa.

The behaviour of cellulose was studied in water at high temperatures and high pressures by in situ high-resolution optical microscopy. It was found that crystalline cellulose underwent transformation to an amorphous state in hot and compressed water, which was followed by complete dissolution. The finding shows that the chemical stability of cellulose in hot and compressed water is determined by the unique properties of cellulose that arise from extensive networks of hydrogen bonds among the cellulose chains in the crystal. The implications of the observation for hydrothermal conversion of cellulose are discussed.