Alkaline Peroxide Treatment for Improving the Papermaking Properties of Recycled Unbleached Softwood Kraft Pulps

Abstract

The main shortcoming of the papermaking properties of recycled fibres refers mainly to the hornification effect, as a consequence of drying during papermaking. An alkaline treatment is potentially useful to reverse this effect. The present paper discusses the consequences of alkaline and alkaline peroxide treatments on unbleached recycled softwood kraft pulp (Kappa number: 92). A 32 factorial experimental design was applied, on considering the following factors: a) total alkaline charge and b) total peroxide charge. The chemical oxygen demand values were used for evaluating the material loss. It was found out that the delignifying effect of alkali was enhanced by peroxide addition. The alkaline treatment reduced freeness and improved the papermaking properties, such as tensile strength, Concora crush strength and short column compressive strength. Also, the addition of peroxide increased the papermaking properties even more, while the material loss caused a considerable increase in the organic charge of the effluents.