Hydrocyclone separation, and reject refining, of thick-walled mechanical pulp fibres

The use of hydrocyclones for fractionation of mechanical pulp fibres on the basis of structural fibre characteristics such as fibre wall thickness, wa s studied in two different mills using commercially available hydrocyclones . The results indicate that the technique may be used for removal of thick- walled fibres, harmful for paper smoothness. The fraction of thin-walled ea rlywood fibres were significantly larger in the accept than in the reject f lows. Fibres with broken circumference are predominately thin-walled, and w ere accumulated in the accept flow. By reject refining at high and low cons istency, the wall thickness of the reject fibres was significantly reduced.