Influence of beech wood quality on bisulfite dissolving pulp manufacture. Part 1: Influence of log storage on pulping and bleaching

The present study investigated different log storage conditions and their influence on the processability of the wood material in pulping and bleaching. For that purpose, logs were stored for about 15 months under dry and wet conditions. Besides a detailed chemical, physical and microbial characterization of the wood, cooking trials according to the standard magnesium acid bisulfite process and bleaching experiments at various conditions using a (E/O)-Z-P-sequence were performed. The dependency of pulp yield, delignification efficiency, the course of cellulose depolymerization and brightness on the different storage conditions was evaluated. Bleaching selectivity was comparable for pulps made from fresh and wet-stored wood. In the case of pulp made from dry-stored wood, between 60% and 300% more bleaching chemicals, expressed as OXE, were necessary to obtain the target brightness. Milled wood lignin was isolated from the beech wood samples to study possible structural changes attributable to different storage conditions. Permanganate oxidation was applied to investigate the most important lignin structures. Additionally, preliminary NMR studies were performed to gain supplementary information about the composition of the lignin moieties. UV microspectrophotometry in agreement with absorption difference spectra strongly suggests that the chromophore structures present in both unbleached and bleached pulp samples predominantly originate from polyphenolic compounds, which are attached to the cell wall and are deposited in the lumina of parenchyma cells. From the results obtained so far, it can be concluded that wet storage of beech wood logs efficiently prevents the formation of chromophore compounds which negatively affect acid bisulfite pulping.