Method of producing peroxide bleached pulp

In the method of producing peroxidebleached pulp in a defibrating apparatus in which ligno-cellulosic raw material such as wood chips impregnated with a peroxide-containing bleaching solution is disintegrated in a grinding space defined between a pair of grinding discs which discs rotate relatively to one another under axial pressure within a closed defibrator housing in an environment of pressurized steam at a temperature above 100.degree. C., the raw material being compressed at a temperature below 100.degree. C., while being conveyed into an inlet to the defibrator housing and accelerated radially outwards in the grinding space by the centrifugal force created by the rotating discs, the resultant grist being discharged from the defibrator housing through valve means which are controlled to maintain a predetermined pressure within the housing, the improvement comprising:

• (a) compressing the raw material into a steam-tight plug at the inlet to said defibrator housing while advancing it into said defibrator housing;
• (b) breaking up said steam-tight plug into fiber bundles after said steam-tight plug has entered into said grinding space;
• and
• (c) introducing the peroxide-containing bleaching solution into said grinding space without substantial contact with the steam environment in the defibrator housing to react with the raw material during its accelerated radial progression through said grinding space so as to provide a relatively short reaction time betweeen said peroxide-containing bleaching solution and said raw material for achieving a favorable relation between the bleaching action and the decomposition of the peroxide.