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.
Acidic group topochemistry and fibre-to-fibre specific bond strength
Nous donnons ici la description d'une technique d'introduction selective des groupes d'acide carboxylique sur les fibres de pâte kraft. En nous servant d'une nouvelle technique faisant appel a la microscopie electronique a balayage et a la spectrometrie RX a energie dispersive (SEM-EDS), nous avons confirme la topochimie des groupes acides. L'essai de resistance du papier a montre que l'introduction selective des groupes acides sur la surface exterieure de la fibre ou a proximite pouvait ameliorer grandement la force specifique de cohesion interfibres.
Structural Changes in Lignin During Kraft Cooking. Part 5. Analysis of Dissolved Lignin by Oxidative Degradation
Abstract Kraft lignins have been isolated from the black liquors obtained a) after normal kraft cooking of pine wood to different yield levels and b) after a flow-through cook. After purification, the two series of lignins have been subjected to oxidative degradation in a four step reaction sequence leading to the formation of substituted aromatic carboxylic acid Methyl esters. The yields and distribution of the different esters obtained from the flow-through cook indicate that in kraft cooking the lignin which goes into solution undergoes structural changes which coincide with the transition points between the initial, the bulk and the final delignification phases. From the other series of cooks, changes in the frequency of occurrence of the individual esters were also observed as the cook proceeded. These changes could not, however, be attributed to the different phases of delignification but took place rather continuously during the cook. The observed results are discussed with reference to known featu...