Resistência ao intemperismo artificial de quatro madeiras tropicais: o efeito dos extrativos.

Abstract

RESUMOAs madeiras tropicais: garapeira (Apuleia leiocarpa), tauari (Couratari stellata), itaúba (Mezilaurus itauba) e marupá (Simarouba amara) foram selecionadas para examinar o efeito da presença dos extrativos na variação de cor e no processo de fotodecomposição das suas superfícies. Amostras com e sem extrativos foram submetidas a ciclos de radiação ultravioleta (350 nm) e água até totalizar 2.000 horas de irradiação e 400 horas de lixiviação. A mudança da cor natural das madeiras foi monitorada por espectrocolorimetria de reflexão difusa. Amostras de marupá e tauari com teores de extrativos menores que 2% exibiram variação de cor com o aumento do tempo de tratamento quase iguais às amostras sem extrativos. A resistência anormal do tauari à alteração de cor não pode ser atribuída aos seus extrativos. Para a garapeira e para a itaúba, a presença de 11,7 e 7,42% de extrativos respectivamente acelerou a velocidade de variação de cor. A análise dessas variações de cor indica que os extrativos, nesse caso, agiram acentuando a cor natural da madeira. Adicionalmente, verificou-se que o tauari foi a madeira mais resistente à variação de cor do grupo estudado, seguido pela garapeira, marupá e itaúba todas com extrativos. Palavras-chave: cor; sistema CIE-L*a*b*; fotodegradação; madeiras tropicais. ABSTRACTThe tropical woods Apuleia leiocarpa, Couratari stellata, Mezilaurus itauba and Simarouba amara were selected to examine the effect of the presence of the extractives in the color variation and in the photodecomposition process of their surfaces. Samples with and without extractives were submitted to cycles of ultraviolet radiation (350 nm) and immersion in water until totalizing 2,000 hours of irradiation and 400 hours of water leaching. Changings in the natural wood colors were monitored by diffuse reflectance spectroscopy. Samples of Simarouba amara and Couratari stellata with extractives content of 2% or less showed color variation with time of treatment almost similar to the samples without extractives. The abnormal resistance of Couratari stellata to color changing can not be attributed to extractives. For the Apuleia leiocarpa and Mezilaurus itauba woods, the presence of 11,7% and 7,42% of extractives compounds, respectively, accelerated the color variation rate. Analysis of the color variation indicated that the extractives, in this case, acted by intensifying the natural wood color. Additionally, it was verified that Couratari stellata was the more resistant wood to color variation in this studied group of woods, followed by Apuleia leiocarpa, Simarouba amara and Mezilaurus itauba, all with extractives.Keywords: color; CIE-L*a*b* system; photodegradation; tropical woods. INTRODUÇÃOA exposição de madeiras ao ar livre dá início a um processo complexo de decomposição física, química e mecânica denominado de intemperismo (FEIST e HON, 1984). Esse processo é causado pela ação combinada do oxigênio, da fração ultravioleta da radiação solar, umidade, poluição atmosférica e vento, que induzem a descoloração e a deter...

Agrupamento de madeiras tropicais comerciais pela cor

“…The only species analyzed in both studies grouped at the same color name was Erisma uncinatum wood (Yellowish olive). The color of Apuleia leiocarpa and Mezilaurus itauba wood also didn't follow the pattern observed by Barreto & Pastore (2009). The authors reported a yellow and dark reddish-brown color, respectively.…”

“…Brightness values (L*) were similar in general, but Dipteryx odorata tend to be darker and Hymenaea courbaril lighter than wood on literature. Barreto & Pastore (2009) also evaluated the color of Apuleia leiocarpa and Mezilaurus itauba wood. Both species also showed lower values of L*, a* and b* than the ones observed in this study.…”

Wood Colorimetry for the Characterization of Amazonian Tree Species: A Subsidy for a More Efficient Classification

“…Extractives are the main chromophores components that interfere in these indices of colorimetry analysis (PINCELLI et al, 2012), especially in red pigmentation (YAZAKI et al, 1994). According to Barreto and Pastore (2009), the extractives of Brazilian tropical tree species are very diverse, both in quantity and chemical nature. 0.82) and, Amorim et al (2013) for Eucalyptus grandis and Pinus caribea (r = 0.70) woods, corroborating the results found in this research for tropical woods.…”

Correlation and modeling between color variation and quality of the surface between accelerated and natural tropical weathering in Acacia mangium, Cedrela odorata and Tectona grandis wood with two coating

“…Wood color and finish assessments in accelerated weathering conditions have been mostly performed on species from temperate regions among which the most outstanding are Betula pendula , Cryptomeria japonica and Picea albies . Studies on tropical woods are scarce, with only limited references from Barreto and Pastore regarding the accelerated weathering of Apuleia leiocarpa, Couratari stellate, Mezilaurus itauba, Simarouba amara and from Valverde and Moya regarding NW of Cedrela odorata and Carapa guianensis with the application of various finishes.…”