Strength enhancement of fiber network by carboxymethyl cellulose during oxygen delignification of kraft pulp
Sorption of carboxymethyl cellulose (CMC) on the fiber surface was applied during oxygen delignification to enhance the strength properties of softwood kraft pulp. Unlike many previous efforts, the focus was not set on the improvement of selectivity of oxygen delignification, i.e. retaining stable viscosity vs. decreasing kappa number. Instead, without an improved selectivity, handsheets from CMC-treated fibers exhibited a 15% improvement in tensile index and 25% improvement in tear index after a full bleaching sequence in comparison to the untreated reference pulp. Since it is demonstrated that the CMC addition can be incorporated as an integral step in the fiberline process, the method offers an effortless and viable option to produce pulp resulting in stronger paper products.
Structural changes in residual kraft pulp lignins. Effects of kappa number and degree of oxygen delignification
Softwood kraft pulps in the kappa number range of approximately 10-50 were prepared in the laboratory. On subsequent oxygen delignification using single or double oxygen stages, the conditions were ...
The kinetics of lignin reactions during oxygen bleaching
Abstract The reactivities of different lignin model compounds with oxygen in alkaline media have been compared. Generally, phenolic structures with a conjugated side chain like stilbene and enol ethers react very rapidly during oxygen bleaching, whereas structures like propylguaiacol and β-aryl ethers are more resistent. Some of the reaction mechanisms involved are probably of a radical type because new crosslinked structures can be formed with even lower reactivity. The influence of metal ions on the reactivity has also been studied. We have found that Mg2+ and transition metal ions like Mn2+, Cu2+ and Fe2+ influence the rate of degradation as well as the rate of dimerization. Most of the metal ions gave a lower rate of degradation as measured at pH 11. The addition of a small amount of hydrogen peroxide to the oxygen alkali system increases the rate of degradation.