decompression this insures the transport of the product towards the exit without causing any explosion the product can thereafter be cooled down by water injection and further transported for the next step in one embodiment of the present invention a variant of the decompression chambers may be carried out by means of a set of screw spindles and or gears and or inverted pump this variant insures a rapid cooling of the product by a partial decompression with no explosion of the latter the mixing can then start and the reactor is cooled down to around 60 u00b0 c by adding water to recover all the cellulose present in the reactor when the treated pulp is a pulp of sulphite or bleached kraft quality it preferably is sent directly to filtration before going to u201c brightening u201d and or bleaching in the case of a pulp of intermediate quality it is preferable to treat the pulp with a caustic soda solution that is diluted in a way to eliminate leftover lignin and other impurities present after which the pulp is filtered then washed before being sent to bleaching which will be done according to the initial quality of the starting cellulose after filtration the product is brightened with hydrogen peroxide for example using the following conditions the treatment could be done between 60 and 120 u00b0 c and under air or oxygen pressure reaching up to 120 psi the brightening and bleaching process can be adapted in function of the quality of the initial product and in the more extreme cases known bleaching methods can be used such as hypochlorite or chlorine dioxide bleaching the bleaching consistency will preferably be 25 but this can also be done.