The Effect Of The Hydrothermal Pretreatment On Properties Of The E.grandis×E.urophylla Lumber

Eucalyptus,the general designation of the Myrtaceae Eucalyptus plants,is one of the three fast-growing world renowned species.In recent years,with the contradictions of the timber supply and demand increasing, Eucalyptus gradually became popular in the market.However,Most of the Eucalyptus is only use in the pulp wood or wood-based panels,because the difficulty in wood drying during the entity processing.Therefore, Study on the Eucalyptus board drying is meaningful to the entity processing of the Eucalyptus and enhancing its economic value added.In this thesis,eucalyptus boards were taken as researched object and the its drying properties,pretreatment technologies were studied.The samples were dried under 100℃test which were pretreated by 48h frozen then 48h soaked,48h frozen only and controlled one(unpretreated)respectively.It showed that the frozen & soaked was the best. So the drying schedule was made for the next phase of experiment based on this result.After pretreated(cooked under the different water thermochmistry treatment conditions with the same solution prescription),all the frozen & soaked samples were dried under the environment with constant temperature and humidity(T=55℃,φ=40%),The result showed:The drying rate turning point of the pretreated wood declined much;most the tangential shrinkage rate became small,the radial shrinkage rate increased therefore,the ratio of tangential to radical shrinkage rate declined,Also,the extract content of the pretreated wood decreasd,it is means that the permeability of the treated wood increased;Another,the bending strength,flexural modulus and the impact intensity of the pretreated wood was in a declining trend, and the max water absorption is increased;In addition,the treatment pretreatment can reduce the residual stress;At last,surface crack and the deformation and other defects of the pretreated wood decreased during the constant temperature and humidity drying,but the treatment temperature can not be too high,the 100℃treated wood appears varying degrees of deformation and even the shrinkage defects on the contrary.The three types of steaming treatment were used,that is to said,the steaming pretreatment before the drying,the intermediate stage steaming when the moisture content is reduced about to the 1/3 intial M.C., and the steaming after end of the drying.The results showed:the drying rate turning point of the pretreated wood decline to a larger;the bending strength and the flexural modulus of the treated wood is in a increasing trend,and the impact intensity is decreased;most the tangential shrinkage rate becomes larger,the radial shrinkage rate reduces,therefore,the ratio of tangential to radical shrinkage rate declined;at the same time, the streaming treatment can reduce the residual stress;also,the max water absorption is increased,in another words,the penetrability of treated wood is enhanced. At last,the mechanism analysis of the performance change showed,①In the micro structure figure, Some pits membrane of the better boiled wood rupture,but the cell wall doesn't;and the pits membrane and cell wall of the worse boiled wood are also destroyed,so is the un-boiled wood;while minorities pits membrane of the better streaming wood rupture,but the cell wall doesn't;and to the worse streaming wood, not only the pits membrane but also the cell wall appears crack;and the cell wall of the un-streamed wood is destroyed relatively seriously.②the determination of crystallinity:the crystallinity & crystalline index of treated wood is larger than the untreated wood.③IR spectrum analysis:after the high temperature cooking or streaming and drying,the crystallinity of the wood increase,with this,the combination of the -OH maybe added,and the -OH energy may decrease slightly,this will make the corresponding wave-numbers reduce; Similarly,with the the crystallinity of the wood increase,the possibility of a hydrogen bond produced by the carbonyl and the hydroxy aggrandize,also make the energy of the C=O decrease,and the corresponding wave-numbers reduce.