STUDY OF THE DISCOLORATION BEHAVIOUR OF TEAK WOOD (TECTONA GRANDIS LINN. FIL.) CAUSED BY SIMULATED SUNLIGHT

To investigate the discoloration behaviour of teak (Tectona grandis Linn. fil.) during irradiation, teak veneer specimens were exposed to xenon lamp light simulating sunlight for 80 h and subsequently analysed with a colorimeter. The colour changes were explained by recording Fourier transform infrared (FTIR) and gas chromatography-mass spectrometry (GC-MS) spectra at different exposure times. Forty hours of simulated irradiation marked a key point in the colorimetric analysis. During irradiation of 40 h, the increase in the CIELAB parameters Delta a* and Delta b* originated from the generation of carbonyl derivatives that were determined by FTIR analysis. Besides that, by combining GC-MS and microscopic analyses, the decrease in Delta L* in the first 20 h resulted from extractives migrating from the interior to the surface, and that the subsequent increase in Delta L* mainly arose from volatilization of the extractives. Additionally, the decrease in Delta b* after another 40 h of irradiation was mainly due to decreasing volatile extractive contents. Our conclusion reveals the causes of photo-induced discoloration in teak.