Chlorine dioxide bleaching of soda-anthraquinone jute pulp to a very high brightness.
Bleaching of soda-anthraquinone jute pulp by chlorine dioxide (ClO2) was studied to reach a target brightness of above 88% for the purpose of using less bleaching chemicals. The performance of either chlorine dioxide or peroxide in the final bleaching to boost brightness was also studied. The experimental results revealed that the final brightness depended on ClO2 charge in the Do and D1 stages. The brightness reversion was lower when the final stage brightening was done by peroxide. The use of Mg(OH)2 in the D1 and D2 stages improved the final brightness due to the formation of less chlorate and chlorite during the Mg(OH)2- based ClO2 brightening stages. The strength properties of pulp bleached by peroxide in the final stage was slightly better than that from ClO2 as the final ClO2 bleaching stage.
PRESENCE OF HARDWOOD CHIPS AND ITS IMPACT ON PULP STRENGTH PROPERTIES IN THE PRODUCTION OF BLEACHED SOFTWOOD KRAFT PULP
The effect of hardwood admixture (15-25% birch or aspen) in kraft cooking on the strength properties of the fully bleached pulp was investigated. Results obtained from both lab- and mill-processed ECF bleached pulps showed that adding 15-25% birch or aspen to the production of fully bleached softwood kraft pulp had a minor effect on the strength properties. No significant effect was observed for the hardwood admixture on the apparent density over a wide range of breaking length. Under the conditions studied, the results showed that pulping of mixed softwood/hardwood chips (chip blending) resulted in overall better strength properties than the pulp blending at a given freeness. It was hypothesized that the softwood fibers would be cooked to a higher kappa number in the cooking of mixed softwood/hardwood chips for the same target kappa number, thus having higher fiber strength due to higher pulp viscosity and preservation of the hemicellulose. This was supported by the results from zero-span tensile strength of the long fiber fraction of the samples from chip blending and pulp blending. The implication is that some softwood kraft pulp mills can add up to 25% of hardwood chips to the kraft cooking of softwood chips without significantly affecting the overall pulp strength properties.
Substitution of aspen high-yield pulp for hardwood kra pulp in fine papers and its effect on AKD sizing
What is the effect on alkyl ketene dimer (AKD) sizing of substituting aspen high-yield pulp for hardwood kraft pulp? The degree of sizing was found to be higher for sheets containing high-yield pulp than for sheets made without it. The addition of polyethyleneimine (PEI) prior to AKD addition further improves the degree of AKD sizing of sheets containing high-yield pulp. PEI was added to the high-yield pulp alone as well as to a mixture of high-yield pulp and kraft pulps. Differences in sizing efficiency between these two approaches were attributed to the two distinct functions of PEI: neutralization of anionic trash in the high-yield pulp and sizing promotion for AKD. Precipitated calcium carbonate (PCC), used as filler, had an adverse effect on AKD sizing of sheets made both with and without high-yield pulp.