Intemperismo acelerado em madeira termorretificada em óleo

Abstract

The use of oil heat treatment aims at incrementing the technological properties of wood with use indication for external environments. Therefore, the current study had, as its objective, the evaluation of accelerated weathering on the oil heat treated woods of Pinus elliottii and Eucalyptus grandis. To that end, specimens were manufactured from five trees of each species. The heat treatment was conducted in a laboratory oil bath at 150º, 180º and 210º for four hours and the weathering was conducted in an accelerated weathering chamber for 20, 40 and 60 cycles of twelve hours, the control samples were stored in an air-conditioned chamber (20º and 65% RH). Were conducted: mechanical test (static bending), physical tests (basic specific mass, equilibrium moisture content, swelling and volumetric variation) and surface test (colorimetric testing). The statistical analysis was carried in a factorial arrangement 4x4, with four levels on each factor (temperature and time), in case of interaction a regression analysis was conducted. The main results demonstrate that the accelerated weathering did not affect the mechanical properties, however the heat treatment caused a reduction of resistance on Eucalyptus grandis in accordance with the temperature increase. The physical properties were enhanced with heat treatment, and broadly had little influence of the exposition time. The specific mass increased according to the oil absorption by the wood. The equilibrium moisture content decreased with the temperature rise and presented larger variations on the initial cycles of accelerated weathering, tending to stabilise. Swelling and volumetric variation were improved by the heat treatment and presented little influence of the accelerated weathering. Wood colouration was altered by heat treatment and also by accelerated weathering. The rise in temperature made the woods darker, demonstrated by the reduction parameter L* and the longer exposition time made the wood opaquer and greyish – increased L* and reduced a* and or b*. Thus, the oil heat treatment altered, in a pronounced way, the technological properties of the studied woods and was efficient in its conservation against the action of weathering. Therefore, the use of oil heat treated wood (preferably with a temperature of 180ºC) is recommended for external and internal environments.