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.
Using Optical Brightening Agents (OBA) for Improving the Optical Properties of HYP-Containing Paper Sheets
High yield pulps (HYP) with different brightness levels were used to replace hardwood bleached kraft pulp to determine the influence of HYP substitution on the optical properties of paper products. The effects of OBA, PCC filler, and dyestuff on paper brightness, whiteness, and colour shade were investigated under various HYP substitution rates. The HYP substitution decreases the brightness and CIE whiteness of paper sheets, particularly at a high HYP substitution rate (e.g. 30%). The brightness loss due to the HYP substitution can be recovered by the addition of OBA and/or PCC.
The presence of dissolved and colloidal substances in BCTMP and their effect on sizing
Puisque la pâte mecanique contient davantage de substances dissoutes et colloidales (SDC) que la pâte kraft blanchie, la caracterisation de la teneur en SDC de la pâte chimico-thermomecanique blanchie (PCTMB) et ses effets sur le degre de collage sont inclus dans la presente etude. Nous demontrons que la presence de SDC a un effet negatif sur le collage par ester de resine a un pH allant de neutre a alcalin. Plus la teneur en SDC est importante dans la PCTMB, plus la teneur en colle des feuilles d'essai correspondantes et le degre de collage sont faibles. Toutefois, l'addition de polyethylenimine peut reduire l'effet negatif des SDC sur le collage. Par ailleurs, le poly-DADMAC est efficace pour retenir la colle en presence de SDC, mais pas du tout pour ameliorer le collage. Les resultats microphotographiques indiquent que les SDC ont tendance a absorber de preference les particules de colle, entrainant ainsi une reduction de l'efficacite du collage.