COMPARATIVE EVALUATION OF TCF BLEACHED HARDWOOD DISSOL’t’ING PULPS

With an annual production of some 3.5 million tons between 1990 and 1995, dissolving wood pulp accounts for only 2% of the total wood pulp production. However, the high demands for cellulose purity and reactivity as well as its manifold routes of utilization are the reason for the advanced state of technology within the pulp industry. For dissolving pulp production, only acid sulfite and prehydrolysis kraft processes (PHK) are of major practical importante. Unlike Paper grade pulping the acid sulfite process is the dominant process for the production of dissolving pulps and accounts for approximately 60% of the total production. The quality Profile of both types of dissolving pulps made from eucalyptus species was studied with respect to their Chemical composition, cellulose structure at molecular, supramolecular and morphological level, alkaline oxidative degradation kinetics and the course of heterogeneous derivatization reactions. In comparison to PHK, acid sulfite pulps generally showed a higher level of viscosity in combination with a higher fraction of low molecular weight cellulose indicated by the low RIO content, the high differente between R18 and RlO, the high topper number and the broad molecular weight distribution (GPC). Supramolecular structure (cellulose 1 to Nacellullose 1 lattice transition) and cellulose morphology (electron micrograph) of both categories of pulps approach one another with increasing prehydrolysis intensity in case of PHK pulps. Aging experiments revealed that pulps of high polydispersity (sulfite pulps) are characterized by a rapid viscosity degradation down to a level of 320-350 ml/g resulting in a sharp decliine in polydispersity. Consequently, the aging degradation mechanism based on number-average degree of polymerization seems to be rather independent from the origiin of pulp and strictly follows a Zero-Order rate equation. In gleneral, viscose made from PHK pulps show ed a lower content of undissolved particles compared to viscose made from sulfite pulps probably due to higher alkali resistance. Acetylation efficiency was characterized by the coefficient of yellowness of cellulose triacetate Solution. Color intensity was found to correlate linearly with pentosan content, morc or less independent of pulp origin.