INFLUENCE OF BLEACHED SOFTWOOD AND HARDWOOD KRAFT PULPS ON TISSUE PAPER PROPERTIES

The properties of bleached softwood and hardwood kraft pulps at different drainage resistance were compared. Bleached softwood kraft pulps required twice as long time as bleached hardwood kraft pulps, in laboratory beating, to achieve the same drainage resistance. The softwood pulp from a mixture of pine and spruce had the highest dry and wet tensile strength, which was slightly lower than the tensile strength of the pine pulp. The birch pulps had higher dry and wet tensile strength than the pulps from eucalyptus and beech. The bleached softwood kraft pulps had higher fibre strength and fibre length than the hardwood kraft pulps, whose fibres had a higher fibre bonding ability. The water absorption and bulk softness of the bleached hardwood kraft pulps were higher in comparison with those of softwood kraft pulps. The highest water absorption had the bleached kraft pulps from eucalyptus and beech, while the pulps from birch had the highest bulk softness. The bleached hardwood kraft pulps with high bulk softness were characterized by low optical surface variability, while the softwood pulps with low bulk softness had high optical surface variability. Among the tested bleached kraft pulps, the birch and beech pulps had higher brightness than the pulps from eucalyptus, pine and the mixture of pine and spruce. Pulp beating increases the tensile strength, while reducing the water absorption, bulk softness and brightness. Therefore, it is recommended to beat the pulp for tissue paper production to achieve only low drainage resistance, which depends on the type of tissue paper products.