Abstract

This study aims to investigate the causes of the differential behavior of extractives on the water resistance of the welded joints of three tropical woods. The welded joints of these chemically characterized woods were obtained by rotational dowel welding. The respective extractives contents obtained during the successive extractions were 12.98 ± 0.90% for Iroko, 17.36 ± 0.40% for African pearwood and 18.16 ± 1.00% for Padauk. Phytochemical screening revealed a high concentration of polyphenols in the extractives of Padauk and Iroko compared to African pearwood. The highest delamination rate (76.66%) was obtained with African pearwood. The highest tensile strength before (4.09 MPa) and after (1.94 MPa) the delamination test was obtained with Padauk. MALDI-TOF mass spectrometry analysis revealed non-leaching after 30 days in cold water of lignin and hemicelluloses fragments from Padauk at 536 Da and 698 Da, but just for hemicelluloses fragments as shown by a glucose pentamer at 837 Da, a glucomannan fragment, and of a glucose pentamer with a xylose residue attached at 970 Da that disappeared completely after 30 days of African pearwood water immersion. However, cold water immersion of Iroko appears to remove resveratrol at 250 Da, a stilbene, as well as multiprotonated stilbene at 256 Da while other stilbene class polyphenols such as geranyl trihydroxy stilbene at 364 Da and chlorophorin at 379 Da seem unaffected by water. SEM analysis confirmed perfect adhesion of Padauk and Iroko joints which indicates a strong correlation between the water resistance of the welded joint and the type of extractives.

摘要

本研究旨在调查提取物对三种热带木材焊接接头耐水性的不同​​行为的原因。这些化学特征木材的焊接接头是通过旋转定位销焊接获得的。在连续提取期间获得的相应提取物含量分别为 Iroko 的 12.98 ± 0.90%、非洲梨木的 17.36 ± 0.40% 和 Padauk 的 18.16 ± 1.00%。植物化学筛选显示，与非洲梨木相比，紫檀和伊罗科提取物中的多酚浓度较高。非洲梨木的分层率最高（76.66%）。使用 Padauk 获得分层测试之前 (4.09 MPa) 和之后 (1.94 MPa) 的最高拉伸强度。MALDI-TOF 质谱分析显示，来自 Padauk 的 536 Da 和 698 Da 的木质素和半纤维素片段在冷水中 30 天后未浸出，但仅对于半纤维素片段，如 837 Da 的葡萄糖五聚体、葡甘聚糖片段和在 970 Da 处附着木糖残基的葡萄糖五聚体在非洲梨木水浸泡 30 天后完全消失。然而，Iroko 的冷水浸泡似乎可以去除 250 Da 的白藜芦醇，一种二苯乙烯，以及 256 Da 的多质子二苯乙烯，而其他二苯乙烯类多酚，如 364 Da 的香叶基三羟基二苯乙烯和 379 Da 的叶绿素似乎不受水的影响。