Abstract: A process for preparing chemithermomechanical pulp comprising subjecting a lignocellulosic substance from which said pulp is to be formed to the simultaneous action of a sulfite and a reducing agent that is more electronegative than the sulfite ion during a nondestructive cooking operation at a temperature of about 100.degree. C. or above under saturated steam pressure; said simultaneous action taking place at an initial pH of between 7 and 12.5.

Abstract: A process for bleaching a lignocellulosic matter in the form of a mechanical, thermomechanical, chemicomechanical or chemicothermomechanical papermaking pulp, or of wood chips while being converted into one of these pulp types by processing in a machine consisting essentially of two interpenetrating spiral surfaces wound around parallel shafts driven in synchronous rotation in the same direction inside a barrel which encloses them, and determining between upstream and downstream in the direction of forward travel of the matter a series of zones for drawing and braking the matter, which comprises combining a bleaching treatment using a reducing agent and a bleaching treatment using an oxidizing agent, characterized in that, after pretreatment using at least one metal-complexing or sequestering agent, the lignocellulosic matter undergoes a washing operation with an efficiency greater than 96% before undergoing in succession a bleaching treatment using a reducing agent at a pH of between about 8 and 12, a washin