A new insight into the bleachability of kraft pulps, Journal of Pulp and Paper Science, February 2003, Vol. 29(2) (619KB)

The bleachability of higher yield chemical pulps has been the subject of several reports, but little effort has been made to assess the changes in bleachability of these pulps across a bleaching sequence, and to correlate these changes with the varying composition and chemical structure of pulps during bleaching. In this work, we bleached four different black spruce pulps—one conventional reference kraft pulp, one high kappa number conventional kraft pulp, one polysulphide (PS) pulp and one polysulphide–anthraquinone (PS–AQ) pulp—using the D₀EoDED and OD₀EoDED sequences. We found that, of the four pulps examined, the PS–AQ pulp had the poorest response to D₀EoDED and OD₀EoDED bleaching. The PS pulp and reference kraft pulp had similar bleachabilities. We also found that oxygen-delignified pulps responded less well to D₀Eo bleaching than the corresponding unbleached pulps. The OD₀EoDED sequence yielded a higher brightness than the D₀EoDED sequence. The different bleachabilities of pulps are attributable to the formation of a covalent bond between hexenuronic acid groups and lignin.