Preservation characteristics of Malaysian timbers
Factors influencing the application of copper(II) and boron-based preservatives to four commercially important timbers of Malaysia viz rubberwood (Hevea brasiliensis), (Koompassia malaccensis), keruing (Dipterocarpus spp.), and dark red meranti (Shorea spp.) were studied. Of the four, only kempas contains a significant amount of extractives; the ethanol-soluble extract reacts with copper(II) solutions to form insoluble Cu(II) complexes. The anatomical features which might influence the penetrability of preservative were shown by optical and electron microscopy to be starch grains, silica grains, gums and gum ducts, tyloses and the nature of pitting on various elements. Among the boron compounds studied, the trimethyl borate-methanol azeotrope gave better impregnation and relatively higher boric acid concentration. Both gas and liquid phase treatment of rubberwood gave a relatively high concentration of boric acid near the surface and a relatively low concentration in the interior. The distribution of copper in the four woods was established by atomic absorption spectrometry and scanning electron microscopy-energy dispersive X-ray analysis. The distribution is similar to that of boric acid in rubberwood. The distribution of copper(II) and the solvent in rubberwood during drying was revealed by X-radiography and chemical analysis. It involves movement of the liquid phase and not simply of the vapour phase. The way in which the treated wood is dried greatly influences the distribution of copper. Drying via the radial and tangential faces results in a relatively high concentration of copper at the periphery leaving the centre with a relatively low concentration.