Avaliação dos efeitos da modificação térmica nas propriedades de diferentes madeiras

Abstract

This study evaluated the effects of thermal modification on the chemical, physical, and mechanical properties of Eucalyptus sp., Pinus sp., and Cedrela sp. woods. The samples were subjected to heat treatments at 140°C, 180°C, 220°C, and 240°C in a reactor system, with a heating rate of 0.3°C/min. Chemical properties were evaluated through FTIR spectroscopy, X-ray diffraction, and thermogravimetric analysis; physical properties were assessed by apparent density, wettability, and colorimetry; and mechanical properties were analyzed through static bending, tension, compression, Janka hardness tests, and wave propagation. The results indicated that heat treatment significantly affects wood properties, varying according to species and temperature. Chemical analyses revealed degradation of hydroxyl groups and modifications in lignin, with a reduction in the crystallinity index. Apparent density decreased in the 220°C and 240°C treatments, especially for eucalyptus and cedar, with significant reduction observed at 140°C for Eucalyptus sp. Wettability progressively decreased with increasing temperature for Eucalyptus sp. and Cedrela sp., while pine showed increased wettability at lower temperatures, followed by reduction at higher temperatures, becoming equivalent to the control. Wood darkening was progressive, with the L* parameter being the most sensitive. Mechanical properties were most affected above 220°C, with the most significant reduction in modulus of rupture, with eucalyptus being the most sensitive species due to the effects of lignin plasticization at lower temperatures. Non-destructive methods showed strong correlation with static tests (R² > 90%). It is concluded that thermal modification is a viable technique to alter specific wood properties, with effects varying according to species and wood treatment temperature