Comparative Study on PFI Beating Response of Hardwood and Softwood Kraft Pulps

The influence of PFI beating on fibre and handsheet properties of hardwood and softwood kraft pulps was investigated. The results indicated that improvement in strength properties by beating is accompanied by deterioration in optical properties. The hardwood fibre response differently to PFI refining when compared to the softwood counterpart. The drop in fibre length is relatively small for both pulps when they are beaten to 17,000 revolutions, but the softwood fibres experience a greater reduction in coarseness (26%) when compared with the hardwood counterpart (14%), at the same time, beating straightens fibres by reducing the curl and kink indices. The rate of drop in freeness is similar for both pulps. When beaten to about 17,000 revolutions, the increase in dry zero-span tensile is greater for softwood (47%) than for hardwood fibres (28%), but the softwood fibres experience a net loss in tear index, while the hardwood counterpart shows about two folds gain. When beaten to freeness about 450 mL, the softwood fibres show a greater decrease in brightness (4%-points) than the hardwood counterpart (2%-points); opacity and light scattering coefficient are substantially higher for the beaten hardwood fibres than for that of beaten softwood fibres.