Environmentally benign treatments for inhibiting the release of aqueous extracts from merbau heartwood

Abstract

Merbau (Intsia spp.) is one of the most valued commercial trees due to its high strength, dimensional stability, and durability. However, one major disadvantage in some applications is that its red aqueous extracts (RAEs) can be easily leached out to stain adjacent materials and discolor the wood itself. Since some plant extracts are known to act as chelators of metal ions, seven metal compounds (FeCl3, FeCl2, FeSO4, CuCl2, CuSO4, AlCl3, and Zn(NO3)2) and two boron compounds (H3BO3 and Na2BO7) were used to evaluate their abilities for minimizing extract-staining. The results reveal that FeCl3, FeCl2, FeSO4, CuCl2, and AlCl3 at the concentration of 1.0 % are effective reagents for chelating the RAEs of merbau. FeCl2 and CuCl2 perform better than the other three metal reagents, and in particular, FeCl2 has excellent reactivity with RAEs. In addition, drying at 100 °C could enhance the bleed resistance of treated wood, and an even more significant effectiveness was observed with CuCl2 treatment. Treatment with 0.1 % FeCl2 and CuCl2 followed by drying at 100 °C are the optimum treatments for inhibiting RAEs in merbau, with weight losses of only 1.6 and 1.7 %, respectively, compared with 13.2 % for untreated wood after a 16-day leaching test. These two treatments were also proven to have good metal fixation ability. Moreover, CuCl2 treatment can enhance the decay resistance of merbau. The treatments explored in this study are environmentally benign and efficient approaches to solving problems caused by the RAEs of merbau heartwood.