Estabilidade da cor da madeira de Pinus modificada termicamente e tratada com nanopartículas

Abstract

The objective of this study was to evaluate the effect of the thermal modification and application of nanoparticles on the color stability of the Pinus sp wood after exposure to ultraviolet radiation in accelerated aging conditions. Wood samples were heat-treated at 180, 200 and 220oC for two hours in a laboratorial electric muffle from Elektro Therm and impregnated with a solution of 1.5% zinc oxide (ZnO) nanoparticles under pressure and vacuum with a T10 WTT cilinder. The material was exposed to ultraviolet radiation during a total cycle of 168 hours, and color measurements were taken each 42 hours. Colour measurements were realized by using the portable spectrophotometer CM 2600d on the CIE L*a*b* space. The physical properties of the heat-treated wood were also determined: density, equilibrium moisture content and their variations after heat treatments and mass loss following treatments. The thermal modification did not affect the wood density, however, heat treatments reduced significantly the equilibrium moisture content. Thermal modification caused mass loss, with average values of 6.2, 8.6 and 12.8% at temperatures of 180, 200 e 220ºC, respectively. Thermal modification caused a gradual darkening on the wood with the increase of the temperature, this could provide greater value to Pinus sp wood by the creation of new color patterns. The wood presented color changes when exposed to ultraviolet radiation during 186 hours. ZnO nanoparticles were not efficient to protect the thermally untreated wood against photodegradation. The ZnO nanoparticles treatment associated to temperature of 220oC was favorable to the stability of the Pinus wood color.