Method for producing nanofibrillar cellulose and nanofibrillar cellulose product

A method for producing nanofibrillar cellulose, wherein cellulose based fibre material, in which internal bonds in cellulose fibres have been weakened by preliminary chemical modification of cellulose, is subjected to disintegration treatment in form of pulp suspension comprising fibres and liquid wherein the fibre material supplied to the disintegration treatment has one of the following properties:

• oxidized cellulose having carboxylate content of at least 0.8 mmol/g pulp or higher,
• carboxymethylated cellulose having degree of substitution above 0.1, or
• cationized cellulose having degree of substitution of at least 0.1 or higher, said method comprising:
• supplying the pulp suspension at a consistency higher than 10 wt-% based on the proportion of the fibres in the pulp suspension and having a content of gas of greater than 10 volume percent, to a disintegration treatment
• detaching fibrils from the fibre material in course of said disintegration treatment by joint effect of repeated impacts to the fibre material by fast moving successive elements and the weakened internal bonds of the cellulose fibres, wherein the fibre material is subjected to repeated impacts successively from opposite directions;
• and
• withdrawing the nanofibrillar cellulose from the disintegration treatment at dry matter which is equal or higher than the consistency of the fibre material.