Improved selectivity of oxygen bleaching through use of chemical additives

Oxygen bleaching is traditionally known to result in loss of strength due to poor selectivity. The purpose of this research is to investigate two different additives (magnesium D-gluconate and tetrasodium 1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP)) as to their impact on the selectivity of oxygen bleaching. The effectiveness of the additives was gauged by measurement of paper strength properties, pulp viscosity, carboxyl group content, carbohydrate content, and generation of hydroxyl radicals. The initial results show that at a given KAPPA number, HEDP addition produces a higher brightness, viscosity and bonding strength than control pulps and reduces the amount of calcium, manganese, aluminum and zinc present. HEDP addition also increases the amount of carbohydrates retained in the pulp, likely caused by a reduction in the generation of hydroxyl radicals. The addition of gluconate produced pulps with a lower viscosity than the control, but higher bonding strength and brightness. Carbohydrate analysis showed a lower carbohydrate/lignin ratio, however, a decrease in hydroxyl radical generation was observed. These results suggest that the HEDP addition is a more suitable additive for oxygen bleaching than magnesium gluconate.