Process for producing differentiated cellulose fibers comprising an enzymatic treatment in association with an acid step

A process for producing cellulose fibers having improved flexibility and strength features comprising:

• at least one enzymatic treatment followed by at least one acid step performed one after another with or without washing of the cellulose fibers between the same, but without any other steps in between said at least one enzymatic treatment and said at least one acid step,
• wherein the retention time during the enzymatic treatment ranges from 40 to 240 minutes the enzymatic treatment is performed in a medium having a pH ranging from 5.5 to 8.5 , having a temperature ranging from 40 to 90° C., and having a hydrolytic enzyme charge ranging from 0.10 to 2.0 kilogram of enzyme/ton cellulose;
• wherein the retention time of the acid step ranges from 20 to 200 minutes, the acid step is performed in a medium having a temperature ranging from 80 to 95° C. and having a pH ranging from 3 to 4.5;
• wherein in the enzymatic treatment a hydrolytic enzyme selected from the group consisting of cellulases, xylanases and mixtures thereof is used;
• and
• wherein the process further includes a step of bleaching the fibers following said at least one enzymatic treatment and said at least one acid step.