Elimination of alum yellowing of aspen thermomechanical pulp through pulp washing

A process for forming bleached thermomechanical bleached aspen pulp having reduced yellowing when subsequently treated with aluminum based chemicals, said process comprising the steps of:

• (a) a thermomechanical refining stage wherein aspen wood chips are thermomechnically refined to form thermomechanical refined aspen wood pulp;
• and (b) a bleaching stage wherein said thermomechanical refined aspen wood pulp is bleached in one or more bleaching stages to form a first bleached thermomechanical refined aspen wood pulp;
• the improvement comprising a washing stage subsequent to said thermomechanical refining stage wherein said thermomechanical refined aspen wood pulp, bleached thermomechanical refined aspen wood or a combination thereof is washed at least once with an aqueous liquid composition, wherein on subsequent treatment of said bleached thermomechanical refined aspen wood pulp with at least one aluminum based chemical said first bleached thermomechanical refined aspen wood pulp has a higher ISO brightness than a second bleached thermomechanical aspen wood pulp formed by the same or substantially the same process as said first bleached thermomechanical refined aspen wood pulp in the absence of said washing stage.