Method for producing a cellulose pulp of selected fiber length and coarseness by a two-stage fractionation

A method of producing a cellulose pulp of selected morphology having an average fiber length between about 0.7 mm to about 1.1 mm, the method comprising the steps of:

• providing an aqueous slurry comprising wood pulp fibers;
• providing a first fractionation stage comprising one of a length classification stage and centrifuging stage;
• directing at least a portion of the slurry to form an input stream to the first fractionation stage;
• processing the input stream to the first fractionation stage to provide an accepts stream of the first fractionation stage;
• providing a second fractionation stage comprising the other of the length classification stage and the centrifuging stage;
• directing at least a portion of the accepts stream from the first fractionation stage to provide an input stream from the first fractionation stage to the second fractionation stage;
• processing the input stream to the second fractionation stage to provide an accepts stream of the second fractionation stage;
• processing the input stream to the length classification stage to provide a length classification stage accepts stream having an average fiber length which is at least 20 percent less than the average fiber length of the rejects stream of the length classification stage;
• and
• processing the input stream to the centrifuging stage to provide a centrifuging stage accepts stream having fibers with a normalized fiber coarseness at least 3 percent less than the normalized fiber coarseness of the fibers in the rejects stream of the centrifuging stage wherein the pulp produced in the accepts stream of the second fractionation stage has an average fiber length between about 0.7 mm to about 1.1 mm and a fiber coarseness that is related to the average fiber length by the relation:
• C<(L).sup.0.3 +0.3
• wherein C is the fiber coarseness measured in milligrams of fiber eight per 10 meters of fiber length.