Abstract:
Heat treatment is a well known process to improve the durability and dimensional stability of less noble wood, The treatment can be applied for heartwood unlike the traditional treatments based on impregnation due to the difficulty of impregnating heartwood.
Pure sapwood and pure heartwood samples were treated in an oven at 190°C and 200°C for 2h, 4h and 6h. Dimensional stability, measured as Anti Shrinking Efficiency (ASE) between 0% and 65% relative humidity, durability, mechanical resistance (MOE an9 MOR) and density were determined for both treated and untreated sapwood and heartwood.
One of the main differences between treated sapwood and heartwood was the presence of resin On the surface of the heartwood treated wood samples. The results showed that for the same treatment conditions the dimensional stability improved more for sapwood than for heartwood. However when the comparison is made at the same mass loss, the differences were not significant. ASEradial reached 80% for sapwood and 50% for heartwood while ASEtangential reached 50% and 40% respectively. In relation to mechanical properties, MOE increased slightly at the beginning of treatment decreasing afterwards, No significant differences were found between sapwood and heartwood. MOR decreased for both heartwood and sapwood reaching almost a 50% and 300/0 decrease for sapwood and heartwood respectively. Once again if the comparison is made at the same mass loss, no significant differences were found be¬tween sapwood and heartwood. Durability against Postia placenta was only evaluated, by the mini-block method, for sapwood and heartwood samples treated at 1900( and 200°C for 2h and 4h. A significant increase in durability was found for both heartwood and sapwood at the higher temperature and for heartwood only at 1900 for 4h.
The results showed that the heat treatment is equally efficient for sapwood and heartwood when comparing at the same mass loss. Since temperature and treatment time influenced differently on heartwood and sapwood i.e. on mass loss, the extent of improvements varied between sapwood and heartwood with the same treatment conditions i.e. the improvement was higher for sapwood.
