QUALITY OF REACTION WOOD IN Eucalyptus TREES TILTED BY WIND FOR PULP PRODUCTION

ABSTRACT This study aims to evaluate the quality of normal, tension and opposite wood of eucalyptus trees lengthwise, in straight and inclined stems, affected by wind action. It also aims to explain the pulping parameters resultant from the quality of the wood. The trees were grouped into four tilt ranges, ranging from 0 to 50º, and the basic density, chemical composition of the wood, and performance in kraft pulping were assessed. Normal and tension wood had similar basic densities; while for opposite wood, the density was lower, being responsible for a decrease in reaction wood density. The chemical composition of the wood was influenced by the presence of reaction wood in the stem. Tension and opposite wood showed lower levels of extractives and lignin and higher holocellulose content when compared to normal wood, with favorable wood quality for pulping. The increase in holocellulose content and the reduction of lignin and extractives content contributed positively to a more delignified pulp and reduction of the Kappa number. However, after cooking the reaction wood under the same conditions as those of normal wood, reaction wood pulping tends to have a lower screen yields. Due to differences in basic density and chemical constituents between opposite and normal wood, it is recommended not to designate the opposite wood as normal wood.

摘要 本研究旨在评估受风力作用影响的桉树直立与倾斜茎干中正常木（normal wood）、应力木（tension wood）及反性木（opposite wood）的纵向材质品质，并阐明由木材品质决定的制浆参数。研究将树木划分为0°至50°的四个倾斜角度区间，对其基本密度（basic density）、木材化学成分（chemical composition）以及硫酸盐法制浆（kraft pulping）性能进行了评估。结果显示，正常木与应力木的基本密度相近；而反性木的密度更低，这也是反应木（reaction wood）整体密度偏低的原因。茎干中存在反应木会对木材化学成分产生影响。相较于正常木，应力木与反性木的抽提物（extractives）与木质素（lignin）含量更低，综纤维素（holocellulose）含量更高，其木材品质更适于制浆。综纤维素含量的提升以及木质素与抽提物含量的降低，有助于获得脱木素程度更高的纸浆并降低卡伯值（Kappa number）。然而，在与正常木相同的蒸煮条件下对反应木进行制浆时，反应木的筛后得率往往更低。鉴于反性木与正常木在基本密度及化学成分上存在差异，建议不要将反性木归类为正常木。