Wood durability varies within and between the species due to the existence of toxic extractives. Wood extractives are known to affect the wood resistance against biological degradation agents such as fungi, insects and marine borers. This study was carried out to determine (i) the natural durability of Neobalanocarpus heimii (King) P.S. Ashton, Eusideroxylon zwageri Teijsm & Binn, and Potoxylon melagangai (Symington) Kosterm, towards fungal decay and termite attack with and without extractives content, (ii) to identify and characterize the chemical compositions and constituents of the soluble fractions of hexane, dichloromethane and methanol from N. heimii, E. zwageri, and P. melagangai extractives, (iii) the determine quantities of extractable extractives compounds from different species using different solvents, and (iv) to assess wood durability from methanol extractives of N. heimii, E. zwageri, and P. melagangai to D. polyphylla. Heartwood samples were cut and ripped to obtain woodblocks of 1 1 1 cm cube. Some of the woodblocks underwent extraction and some were further ground to form a wood meal. The extraction of wood cubes was carried out using a Soxhlet extractor with a different solvent which was 95% Ethanol + Toluene, 95% Ethanol, 95% Methanol and finally hot distilled water in order of increasing polarity. Soil block and termite resistance tests were conducted on both extracted and unextracted N. heimii, E. zwageri, P. melagangai and D. polyphylla woodblocks. Woodblocks were exposed to Schizophyllum commune Fr. (white rot), Trametes versicolor (L.) Lloyd (white rot), and Coniophora puteana (Shum.: Fr.) P. Karst (brown rot), while Coptotermes gestroi Wasmann was used for the termite resistance test. Weight losses due to decay and termite attacks were determined after thirty-two weeks and three weeks of exposure, respectively. Wood meals were subjected to extraction using solvents of increasing polarity, firstly hexane, dichloromethane and methanol. The methanol-soluble extract was used to treat Dyera polyphylla (Miq.) Steenis woodblocks. The removal of extractives content significantly reduced the durability of N. heimii, E. zwageri, and P. melagangai. Woodblocks were more susceptible to termite attack after the extraction of their extractive content. The results from the wood treatment test showed that methanol-soluble extractives successfully treat D. polyphylla woodblocks and at the concentration of 10% it provides excellent protection against wood decay fungi. Gas chromatography/mass spectroscopy (GC/MS) analyses showed that up to 100 compounds were detected in hexane-soluble and DCM-soluble extractives of N. heimii, E. zwageri and P. melagangai. There were more compounds from 103 to 144 were detected in methanol-soluble extractives of N. heimii, E. zwageri and P. melagangai. The major compounds detected in hexane-soluble and dichloromethane-soluble extractives of N. heimi are α-Linolenic acid (5.10%) and 6-Ethyl-3-decanol (6.13%). Major compound detected in hexane-soluble and dichloromethane-soluble extractives of E. zwageri was Isoelemicin (46.81% and 46.83%). Compound 2-Ethoxycarbonyl-3-methyl-4-azafluorenone, 2-fluorenylimime (40.21%) was the main compound in hexane-soluble and dichloromethane-soluble extractives of P. melagangai. Phenol, and 4-methoxy-6-prop-2-enyl-1,3-benzodioxol-5-ol were the major compounds detected in methanol-soluble extractives of N. heimii, E. zwageri and P. melagangai, respectively. There are numerous compounds present in N. heimii, E. zwageri and P. melagangai extractives that are biologically active, protecting them from decay.
AJLAN NURFARAHIN (Sat,) studied this question.