Relationship among Sieber-, Chlorine- and Permanganate Numbers and Lignin Content of Unbleached Pulps

Abstract

Relationships were investigated among Sieber-, chlorine- (chlorine consumption in chlorination by Cl2-water at 0°C for 1 hr. or 20°C for 1/2 hr.) and permanganate numbers and lignin content of various unbleached pulps.The pulps used were prepared from chips of fir, mixture of spruce and fir, birch and mixed hardwoods by sulfite and sulfate processes, ranging in unscreened yield from 46 to 80%.Lignin content was determined by means of UV-absorptiometric method developed by Bethge for sulfite pulp and TAPPI Standard T222m-54 for sulfate pulp.Results are summerized as follows : 1. Sieber number of the hardwood unbleached sulfite pulps is higher about 15-25% than that of softwood unbleached sulfite pulps at the same lignin content, permanganate number or chlorine number at 0°C (Fig. 2, 3, 5 and 6). Sieber number has, however, a linear relationship with lignin content, permanganate number and chlorine number (at 0°C for 1 hr.) in each wood sulfite pulp of Sieber number below 60.2.Permanganate number has a linear relationship with lignin content (Fig. 4, 9 and 12) and chlorine number at 0°C (Fig. 7) in sulfite and sulfate pulps with lignin content below 18 %. Sulfite pulps are, however, slightly higher in chlorine number (at 0°C) and lignin content than those of sulfate pulps at the same permanganate number.3. Chlorine number at 0°C for 1 hr. relates closely with lignin content for both sulfite and sulfate pulps with lignin content below 25 %. This chlorine number corresponds nearly to percentage of lignin in pulp irrespective of the wood species and cooking process (Fig. 8 and. 10).4.Chlorine number at 20°C for 1/2 hr. has also straight line relationship with permanganate number, This chlorine number at 20°C gives, however, slightly higher value (0.5-0.7) than that at 0°C for 1 hr.in the case of sulfate pulps of chlorine number 4 to 8 (Fig. 11).