Aspects of optimisation of mechanical bleach-ing - a comparison of alternative alkali sources for hydrogen peroxide bleaching

摘要

The purpose of this paper is to re-examine the parameters known to influence the result of mechanical pulp bleaching with hydrogen peroxide and to show the advantages and disadvantages of different alkali sources for hydrogen peroxide activation. Consistency, temperature and retention time, hydrogen peroxide and alkali concentrations and the addition of sodium silicate are the main factors to be considered if maximum brightness is to be achieved. Consistency is a very important factor: under the same conditions of temperature, peroxide and alkali concentrations, the final brightness increases with consistency. Given good technical conditions, temperature becomes a critical factor. Above about 75℃, thermal decomposition of hydrogen peroxide becomes significant and the bleaching decreases. This can be offset by adding more peroxide but such addition must be balanced by the addition of alkali and sodium silicate as a stabilising and buffering agent.