The Effect Of Extractives Moving And Structure Change On Color Of Eucalyptus Grandis ×Eucalyptus Urophylla During Prepreheatinging Treatment

Wood color plays a vital role in the commercial use of wood products.Sapwood lumber core difference affecting its processing and utilization.If the saturated steam preheating treatment to reduce the color of wood core material,will improve the utilization of timber and the use of value.In this paper,the effects of water-soluble extract and chemical composition on the color of Eucalyptus grandis×Eucalyptus urophylla during the steam preheating process were discussed,the improvement of color uniformity of preheating treatment was studied.Research shows:(1)The migration position of water-soluble extract varies linearly with temperature and time.Preheating a certain time,at a preheating temperature of 80℃,extract with a more uniform moisture migration in wood.When the preheating temperature is constant,the migration of the extract in the wood tends to be stable and uniform with the prolonging of the preheating time.(2)Preheating process of small molecules of alcohols and ketones from the heart material to the sapwood.Polyphony(cinnamic acid,pyrogallol,dihydrochalcone,ellagic acid,3-benzyl methyl rhodanine,etc.)after preheating treatment,the content decreased,mainly in the distribution of heartwood area,a small amount of migration to the Sapwood,the formation of insoluble in water colored material,so that the eucalyptus core material color difference.(3)In the migration process,the small molecule alcohols undergo the oxidation reaction,a substance containing a C=O group was formed.Acetylene alcohol compound undergoes a nucleophilic reaction to form a substance having C=O and C=C bond conjugated structure,the conjugated system is increased,to increase the absorption of visible light.Polyphenols condensation reaction during the migration process,generating a tannin.Organic hemicellulose hydrolyzate ethanol during migration esters produced by the reaction.(4)After the steam preheating treatment,the relative nonuniformity of the color R is reduced,and the relative unevenness R is 0.448 under the 80 C condition of steam preheating,which is 20.9%lower than that before pretreatment,Color uniformity.