Process for the continuous impregnation of a cellulosic material

A process for the continuous impregnation of a cellulosic material in the form of chips, comprising passing said material continuously through apparatus comprising two parallel meshing screws having identical threads and which are rotated in the same direction inside a sheath which envelops them, said threads of said screws possessing successive zones of different pitch, wherein said material is passed continuously and in succession through a first zone of said screws for feeding and carrying said material downstream, a first braking zone of reverse pitch to the feeding and carrying zone which causes a first compression of said material, at least one subsequent zone for carrying said material downstream, in which, said material is brought into contact with a reagent introduced into said sheath, and a second braking zone of reverse pitch to the feeding and carrying zone which causes a second compression of said material, the braking zones possessing threads provided with apertures for the passage of the material downstream, during each said compression, said material passing through a series of alternate stages of increases in pressure, the relative magnitude of which increases gradually, and of drops in pressure, the relative magnitude of which decreases gradually, and the passage of said material through each braking zone causing a simple separation of said chips, which can assist the squeezing of the chips into said threads without decreasing the length of the fibers, said first compression causing the expulsion, in the upstream direction, of water present in said material, and each subsequent compression causing the expulsion of any spent reagent and of residual liquors present in said material, the overall impregnation treatment causing at least a partial delignification of said material to eliminate substantially completely the effect of shear on the chips.