NMMO monohydrate is used as a solvent in the lyocell process to produce lyocell fiber. It dissolves cellulose to form a solution called dope, and the cellulose is reprecipitated in a water bath to produce a fiber. The process is similar but not analogous to the viscose process. In the viscose process, cellulose is made soluble by conversion to its xanthate derivatives. With NMMO, cellulose is not derivatized but dissolves to give a homogeneous polymer solution. The resulting fiber is similar to viscose; this was observed, for example, for Valonia cellulose microfibrils. Dilution with water causes the cellulose to reprecipitate, i.e. the solvation of cellulose with NMMO is a water sensitive process.
Cellulose remains insoluble in most solvents because it has a strong and highly structured intermolecular hydrogen bonding network, which resists common solvents. NMMO breaks the hydrogen bonding network that keeps cellulose insoluble in water and other solvents. Similar solubility has been obtained in a few solvents, particularly a mix of lithium chloride in dimethyl acetamide and some hydrophilic ionic liquids.