Study On The Influence Of Extractives Components On Discoloration Of Domestic Teak And European Oak

The chemical discoloration of wood is a phenomenon to change the color of wood by utilizing the change of the groups in the components of wood.The use of chemical discoloration had great significance for improving the surface decoration of wood products.In order to clarify the effects of compositions in wood,especially extractives,on the chemical discoloration of wood,domestic teak and European oak were used as the objects.To explore the effect of the extractives on the color difference of the wood,and to identify the main extractives that affected the chemical discoloration of wood,both two species were extracted by the acetone,petroleum ether and other organic solvents.The ingredients and contents were investigated by gas chromatography–mass spectrometry(GC-MS)then.Afterwards,to explore the effect on the color change and the color stability of oak surface treated with various chemical regents.The changes of chemical groups and microstructure of the oak surface treated with Fe₂(SO₄)₃ solution before and after aging and the chemical discoloration of teak irradiated by ultraviolet light were analyzed as well.Through the researches above,the main conclusions were as follow:(1)Teak appeared to be weakly acidic.The difference in content of the main components between heartwood and sapwood of teak was slight.The extractives in heartwood were higher in composition and content than those in sapwood,especially for alkene,phenols,quinones,and ketones.The surface color of sapwood treated by all-trans-squalene solution became closer to the heartwood.All-trans-squalene should be an important extractive that caused the color difference between sapwood and heartwood of teak.As for oak,it was also acidic.The content of total phenol of oak was 7 times higher than heartwood of teak.And the 70%of the total phenol content of oak was tannin,which is the extractives causing the chemical discoloration to oak.The contents and types of extractions in oak were few,which were considerably different from teak.Therefore,the substances that determine the color of the two species were different.(2)UV light has great influence on the color change of heartwood of teak and oak.After exposure to the ultraviolet light,the luminosity L^*of the heartwood of teak surface decreased,while the Red–green coordinate a^*and the Yellow-blue coordinate b^*increased,and basically reached a stable state after 6 hours.The change of various indexes of oak under the ultraviolet light were consistent.But after 96h UV irradiation,the color on the surface of the oak became worse and obviously yellower in a continuous changing trend,which cannot remain stable.Therefore,the color stability of the oak surface was affected by the light exposure.(3)Different effects on the color of oak had been found when treated by different chemical reagents.No obvious relationship between the color of oak after these treatments and the color of the treated reagent was found.The samples treated with different reagents responded differently to temperature and humidity.The surface of the samples treated with Fe₂(SO₄)₃solution were gray-blue,and the color indexes L^*,a^*,b^*of samples decreased as the concentration of treated solution increased,which remained basically stable at the concentration of 6%.The chromatic aberration of the treated sample was bigger than the untreated one at the temperature and humidity accelerated aging.The surface color indexes L^*of all samples decreased and the indexes a^*,b^*increased but unstable with the exposure to the UV irradiation,the chromatic aberration of the untreated samples was the biggest.The higher the concentration of Fe₂(SO₄)₃ was,the smaller the color difference was.(4)The O-H bonds in the extractives of the untreated samples were changed after the temperature and humidity accelerated aging,and the UV accelerated aging was related to the changes of chromophores such as carbonyl and carboxyl groups in lignin and cellulose.After treated with the Fe₂(SO₄)₃ solution,a certain iron complexation reaction was occurred in the lignin,hemicellulose and extractives of the sample,and no obvious reaction between iron and cellulose was found.The extractives,cellulose and hemicellulose of the sample had certain changed during the temperature and humidity accelerated aging.After UV accelerated aging,only tiny variations were discovered in some carbonyl and hydroxyl groups which related to color of the sample,change about lignin was not been found,also small changes in carbon were found.On this experimental condition,the treatment of Fe₂(SO₄)₃ can improve the ultraviolet aging resistance of oak.