Many of the properties that have been described above (cf. "mechanical properties"), in particular natural durability, are due to the inherent extractive content of teak wood.
Substances of content of heartwood are generated through carbohydrates of parenchym cells in the transition areas between sapwood and hardwood and are stocked in the surrounding wood textures (LANGE & SCHWAGER 1997). Lange & Schwager have gained interesting insights concerning contents and constitution of extractive contents in relation to particular teak properties, in particular resistance against destructive fungi.
Extractive contents consist of lipids (terpenoide, fat, wax, fatacides) and /or phenolic connexions (single phenolics, stilbenel, lignane, flavonoide, tannine). There are no structural elements, which could be solved in neutral liquids and /or water, included. The amount of ingredients depends on the type of wood, location, age and season. The most amount of ingredients can be found in core wood, wood ray, root wood, branch formation and at the bark. The above mentioned ingredients define wood colour, smell and durability – as well as quality of pulping and drying and glueing properties.
Plantation teak has shorter felling cycles than naturally grown primeval forest teak. Thus, smaller amounts of extractives become stocked in the wood.
Fig. 1 (BHAT et.al., 2005) shows a comparison of dry and moist teak cultivation areas. Obviously, teak wood grown in moist areas (waterlogging) is less resistant to wood-destructive fungi than teak wood grown on dry locations.
LANGE, W. und SCHWAGER, C. 1997: Akzessorische Bestandteile dauerhafter Holzarten und nicht verholzter Pflanzen mit resistenzwirksamer Aktivität - Eine Literaturstudie. Arbeitsbericht der BFH
BHAT, K.M.; THULASIDAS, P.; MARIA FLORENCE, EJ. JAYARAMAN, K. (2005): Wood durability of home garden teak against brown-rot and white-rot fungi. Trees-Struct Func 19, 654-660
