A process for making defibered pulp material comprising the steps of treating fibrous ligno-cellulosic material with aqueous nitric acid (10,17) having an HNO3 concentration of about 0.15 to 9.0 wt.% and containing aluminium sulphate in an amount of about 0.8 to 1.3 parts per each 10 parts by weight of HNO3, or to alternatively use for grassy fibrous materials nitrate salts such as NaNO3 or KNO3 or NH4NO3, so as to nitrate ligneous component of said material; and thereafter defibering directly, (15,21) or treating the nitrated ligno-cellulosic material with alkali to separate the ligneous component from the cellulosic pulp, and, optionally, recombining a part or all of the ligneous component with the cellulosic pulp.
