Abstract: Method of producing mechanical pulp of improved brightness and light-scattering properties in a defibration apparatus in which wood chips are ground between a pair of discs which rotate relative to one another in a pressurized grinding zone. Prior to the defibrating process, the chips are impregnated with a solution of alkali, selected from the group consisting of sodium hydroxide, alkali silicate, alkali carbonate and alkali bicarbonate, and peroxide, surplus impregnating solution is removed from the chips by compression of the chips, the chips are introduced into a pressure vessel which is in communication with the grinding zone and compressed air is introduced into the pressure vessel in an amount sufficient to maintain the chips in the pressure vessel at a temperature below 90.degree. C. and to maintain superatmospheric pressure within the defibrating zone.

Abstract: A grinding apparatus for producing ligno-cellulose pulp, in which the pulp material, such as wood chips or bagasse, is ground in an environment of steam between a rotating grinding disc and a non-rotating grinding disc enclosed within a housing. Each disc comprises a series of peripherally disposed, radially extending segments provided with ridges and intervening grooves forming opposing grinding surfaces and defining therebetween a grinding space of predetermined width which merges with a central feed-in zone from which the pulp material is propelled by centrifugal force created by the rotating disc, radially outwards through the grinding space.