Durabilidade natural da madeira de cinco espécies amazônicas submetidas a ensaios de intemperismo natural

Abstract

This work aimed to evaluate the natural durability of amazonian tree species Trattinnickia rhoifolia (amescla), Parkia pendula (angelim-saia), Erisma uncinatum (cedrinho), Apuleia leiocarpa (garapeira), Mezilaurus itauba (itaúba) with tests of natural weathering. The specimens for the tests had nominal dimensions of 2 x 2 x 10 cm (thickness x width x lenght); 84 specimens per species were prepared, of these, 12 were used as witnesses for the characterization of colorimetry, roughness and Rockwell initial hardness. In addition to these, samples were prepared in the same dimensions for chemical characterization (holocelulose, lignin, extractives and ash) and physical (basic specific mass). The period of exposure to natural weathering was 240 days, and every 60 days samplings were done on 12 samples per species. On each sampling were analyzed mass loss properties, colorimetry, roughness and hardness. All species showed significant correlation for the mass loss as a function of exposure time, the species amescla, angelim-saia and cedro, showed the greatest reduction of this parameter. The species have your colorimetry, becoming dark (gray shades), less reddish and/or yellowish, with significant correlation with time display and mass loss. With the deterioration process occurred the removal of lignin and extractives by oxidation and leaching, causing surface cracking and consequent amendment of roughness and decreased hardness. The roughness of itaúba and garapeira wood were monitored throughout the weathering period, however for the wood of amescla, angelim-saia and cedro due to severe deterioration, roughness measurement just was possible up to 120 and 180 days. The total variation of color and the weight loss were significantly correlated with hardness for all species, except for itaúba.