IMPACT OF MECHANICAL PULP FINES ON THE EFFICIENCY OF PEROXIDE BLEACHING OF TMP PULP

The efficiency of thermomechanical softwood pulp peroxide bleaching seems to always reach a ceiling. The main objective of this research project is to seek and evaluate the possible reason for such a situation, once known that pulp and paper industry requires higher brightness levels for making new value-added paper. Our assumption is that mechanical pulp fines could be responsible for lower peroxide bleaching efficiency. The first step of the project concerns the evaluation of the impact of peroxide bleaching When using a thermomechanical pulp previously classified by fiber length (Bauer McNett classifier). The results obtained, in terms of optical properties and consumption of peroxide, suggest that, compared to the other fractions of the total thermomechanical pulp, mechanical pulp fines react differently to DTPA pretreatment and peroxide bleaching. There is indication that peroxide bleaching efficiency is related to the composition of the TMP pulp and that the content of mechanical pulp fines will have a high impact on the final brightness level. Several bleaching strategies will be discussed; the bleaching effluents have been recuperated, to measure several environmental parameters such as chemical oxygen demand (COD) and total organic carbon (TOC).