Efeito da termorretificação nas propriedades físicas, mecânicas e na resistência a fungos deterioradores da madeira de Eucalyptus grandis Hill ex Maiden

Abstract

The wood is one of the most versatile building materials, however considering the environmental pressures associated with lack of native wood in the South and Southeast region, alternatives woods must be used. The Eucalyptus species are a solution to this problem however they have limitations such high levels of growth stress, high shrinkage, low permeability, drying defects and susceptibility to rot fungi. A commercially attractive way to improve the dimensional stability and durability of these products is this retification® process after its drying. The objetive of this work was evaluating the effect of retification®, under different temperatures on the quality of the Eucalyptus grandis Hill ex Maiden wood. In order to do it so, were used logs of Eucalyptus grandis trees, with 5.9 years of age from company Duratex-SA. Each board was cutting to provide pieces and those designed with control and retified® with temperatures of 140oC, 160oC, 180oC, 200oC and 220oC. The quality of retified® wood was determined by the following tests (1) mass loss and tickness variation of boards; (2) physical properties (densities at 0%, 12.0% and 17.5% of moisture content, equilibrium moisture content, volumetric and linears swelling, shrinkage coeficient and anisotropic factor); (3) decay resitance of wood; and (4) mechanical properties (compression parallel to grain, static bending and Janka hardness perpendicular to grain). The results showed that: (1) the mass loss of Eucalyptus grandis boards exponentially increases from 0.004% to 5.7% with an increase of retification® temperature; (2) near pith there is a variation in the boards thickness reduction of up 99.6% with an increase of treatment temperature, while near bark this variation was of up to 18.5%; (3) with increase retification® temperature has an significant improvements on moisture content and volumetric, tangential, radial and longitudinal swelling in theirs shrinkage coefficients of up 49.3% and 58.8%, 62.7%, 50.0%, 77.4% and 26.9%, 6.9% and 30.6%, respectively; (4) the retification® between 140oC and 220oC had a decreased of mass loss from 5.1% to 77.4% and from 3.3% to 82.4% for agar-block and soil-block tests with Picnoporus sanguineus fungus, respectively; (5) the retification® with temperatures biggest than 180oC to caused significant decreases from 24.0% to 52.3% in the modulus of rupture in static bending, however no changes were observed on modulus of rupture in compression parallel to grain and neither on modulus of elasticity for both tests; (6) retified® woods with temperature up 180oC to presented some samples with fragiles failures, which were of 100% for heat-treated wood at 220oC; and (7) the temperature increased from 180oC to 220oC caused significant decreases from 12.1% to 20.7% in Janka hardness perpendicular to grain.