Impact of pre-hydrolysis kraft (PHK) conditions on young <i>Eucalyptus</i> clones’ unbleached pulp aiming at dissolving pulp production

Abstract The prehydrolysis kraft process (PHK) is the most widely used industrial method for producing dissolving pulp. Wood prehydrolysis involves the removal of hemicelluloses before kraft pulping, enabling the production of high-quality dissolving pulp. The process performance can be controlled by adjusting the time and temperature parameters. This study evaluates the effect of prehydrolysis intensity on the unbleached pulp quality of eucalyptus clones used for dissolving pulp production. Five trees from two eucalyptus clones ( Eucalyptus urophylla and E. urophylla × E. spp.), aged 3 and 5 years, cultivated in plantations located in Bahia, Brazil, were assessed. Hydrothermal pre-treatments were applied to wood chips under varying time and temperature conditions ( P -factor) to study its effect on kraft pulping and unbleached pulp properties such as yield, Kappa number, viscosity, brightness, pentosan content, and crystallinity index. Increasing the severity of the prehydrolysis process reduced the Kappa number and pentosan content, alongside an improvement of up to 8.6 % in pulp brightness and 7.2 % in the crystallinity index. These findings demonstrate the efficiency of optimized prehydrolysis conditions for dissolving pulp production, particularly for a P -factor of 432.