Relations between Hemieelluloses and Physical Properties of Various Bleached Sulphite Pulps

Abstract

Several softwoods and hardwoods sulphite-type pulps ranging in yield from GO to 46% were bleached with three-stages bleaching process (chlorination, causLie extraction, hypochlorite bleaching, and the comparisons were made on the physical and chemical properties of resulting bleached pulps.Bursting strength of bleached pulps cooked by the same process increases with unbleached pulp yield (Fig. 1 and 2), but such a clear difference is not found generally in beating rate (Fig. 3 and 4.) Water retention values of bleached pulps at the equal healing time or the equal freeness increase, however, with unbleached pulp yield (Fig. 5, 6 and. 7) Conventional acid sulphite pulps are superior than hisulphite pulps in easiness of beating, and their water retention values increase more rapidly than those of bisulphite pulps.The fact, that the alkali soluble hemicelluloses, especially uronic acid contents of bleached pulps increase with unbleached pulp yield, and bisulphite pulps are remarkaidy poor in uronic acid (Fig. 8 and 9), shows the presence of some relations between these hen- icellulcos and water retention (swelling) property of pulp.Water retention value of bleached pulp is closely related with specific scattering coefficient or opacity of the sheet, irrespective of cooking process and unbleached pulp yield (Fig. 11 and. 12). Both water retention value and specific scattering coefficient are related with tensile and bursting strengths of the sheet of bleached pulps (Fig. 10, 13 and 14).It is apparent that the hemicelluloses, especially uronic acids, manifest their effects upon the pulp properties, due to rapid swelling and making of the much bonded area to be developed during beating without much decrease in fiber strength. Tensile and bursting strengths of bisulphite pulps are, however, slightly higher than those of conventional acid sulphite pulps at the equal water retention value or the equal specific scattering coefficient. Sheet density at the equal specific scattering coefficient decrease with unbleached pulp yield (Fig. 15).