A method of manufacturing bleached chemimechanical and semichemical fibre pulp by means of a one-stage impregnation process.

摘要

In accordance with the invention a chemimechanical pulp is produced from lignocellulosic material, for example wood chips, by subjecting the material to a process in which it is steamed, impregnated with alkali and peroxide, drained, pre-heated, refined and bleached.

The material is impregnated in a single stage with solution containing alkali and peroxide. Subsequent to passing an intermediate drainage and reaction stage, the material is pre-heated to a temperature of from about 50°C, but not above 100°C. The material is then refined in one or two stages.

The material can be impregnated by immersing the same in the impregnating solution for a period of up to 20 minutes at a temperature of 15-60°C, or by compressing the material in a screw press and permitting the compressed material to expand in the impregnating solution.

The ratio of alkali to peroxide in the impregnating solution is balanced so as to obtain a pH greater than 12.

The optimal brightness for a given peroxide charge is achieved by a balanced division of the peroxide charge between the chip impregnating stage and the bleaching stage.