Reaction mechanisms inhibiting the release of aqueous extracts from merbau heartwood by iron(II) and copper(II)
Journal
Wood Science and Technology
Journal Volume
51
Journal Issue
3
Pages
653-668
Date Issued
2017
Author(s)
Abstract
Extractive bleeding with adjacent staining from merbau heartwood is a problem affecting exterior applications. Although the inhibition method of the exudate has been performed via complexation of the aqueous extracts (AE) and iron/copper ions, its mechanisms remain unclear. The aim of this study is to clarify the complexation mechanisms of AE with iron/copper ions. The results obtained from both 13C NMR and FTIR analyses show that the primary component of AE is catechin-/epicatechin-based condensed tannin. Further results of the complexation test under heating conditions revealed that the catechol units in condensed tannin of AE could efficiently complex iron ion, forming the bis-bidentate complex, leading to decreased water solubility of AE. However, AE could not complex copper ion to form the insoluble AE–Cu complex directly at ambient temperature, and it relied on the o-quinone, which was derived from the heated AE at 100 °C, complexed with copper ion to form the bis-bidentate complexes.
SDGs
Type
journal article