Oxidação da madeira de Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson por ozonólise

Abstract

This work aimed to realize oxidative reactions using ozone in aqueous middle to simulate the aging aspect in Corymbia citriodora K.D. Hill & L.A.S. Johnson wood samples. Ozone that is a very reactive gas, was produced by the ozonizer by the corona effect. In order to evaluate the transformations occurred in the samples submitted to the treatment in different times and pHs (neutral, basic and acid) those samples were analyzed by various tests (color mensuration in the CIELAB colorimetric space; contact angle between water and wood by the goniometer; XPS spectroscopy and Pyrolysis – GC/MS). The samples were obtained from a Corymbia citriodora tree log harvested in the UFRRJ campus in Seropédica. Those samples were treated mechanically in order to adequate it to the analysis with 10 x 20 x 2 mm dimensions. It was observed that the 6h acid was the one that presented the best natural aging appearance. All the tests done have shown that the wood components had different behaviors in each treatment, especially when we talk about lignin and its G/S (Guaiacyl:Siringyl). The results have shown that the reactions were well succeed, revealing that the ozone had reacted in the majority of the samples, with the lignin, affecting the G/S ratio for all the treatments. XPS data showed the level of oxidation, for example, in the neutral treatment, showing ozone oxidative effect. In this way, the G/S ratio revealed that the ozone attack have occurred, first with the lignins that have predominantly the guaiacyl units, assuming that the reaction affected mainly the cellular region with high guaiacyl units content. It was also detected in the acid treatment, that the ozone as well reached the extractives group, especially the decanoic acids. All the experimentations were sufficient to discolor and give aging appearance to the wood, as the color changing shown by the color tests with the spectrophotometer. The contact angle has proved that the samples in order absorb more water, becoming more hydrophilic, when related to the L:C ratio (lignin:carbohydrate).