Method for producing nanofibrillar cellulose and nanofibrillar cellulose product

In a method for producing nanofibrillar cellulose， cellulose based fibre material， in which internal bonds in cellulose fibres have been weakened by preliminary modification of cellulose， is subjected to disintegration treatment in form of pulp comprising fibres and liquid. The fibre material is supplied at a consistency higher than 10 wt-%， preferably at least 15 wt-%， to a disintegration treatment where fibrils are detached from the fibre material by joint effect of repeated impacts to the fibre material by fast moving successive elements and the weakened internal bonds of the cellulose fibres. The nanofibrillar cellulose is withdrawn from the disintegration treatment at dry matter which is equal or higher than the consistency of the fibre material. In the disintegration treatment， the fibre material is supplied through several counter-rotating rotors (R 1， R2， R3 . . . ) outwards in the radial direction with respect to the rotation axis (RA) of the rotors in such a way that the material is repeatedly subjected to shear and impact forces by the effect of the blades (1) of the different counter-rotating rotors.