Effects Of Heat Treatment On The Water Vapour Sorption Dynamics Of Wood

The amounts of hygroscopic hydroxyl in hemicellulose and amorphous region of cellulose in wood were decreased after heat treatment,hence the hygroscopicity was reduced,the dimensional stability and fungal resistance improved.Heat treatment was a physical technology,environment-friendly and wide application were two advantages of it.However,it was short of researching for the fundamental study about effects of heat treatment on the water vapour sorption dynamics of wood,aiming at the phenomenon,this paper was aimed at analyzing the effects of heat treatment on the water vapour sorption dynamics of poplar and radiata pine,and finding the fundamental reasons for decrease of hygroscopicity and increase of quality in molecular level.The paper aimed to research poplar and radiata pine,which were treated at 200 ? for 4h,8h,12 h and 24 h with nitrogen,the untreated poplar and radiata pine were control group,the heat-treated ones were modified groups.Some tests have been done,there were the changes of moisture content and hysteresis during the whole dynamic sorption run;the changes of unit mass heat flow and heat absorption during desorption process.According to the test results,the author analyzed the effects of heat treatment on the water vapour sorption dynamics of poplar and radiata pine.The results were as follows:The hemicellulose was degraded after heat treatment,therefore the mass loss ratio of poplar and radiata pine were increased and gained 14.5% for poplar after heat-treated for 24 h and 8.6% for radiata pine;when moisture absorption in several saturated salt solutions at different relative humidity,the moisture content and dimensional changes of heat-treated ones were less than that of the control group on account of loss,and both moisture content and dimensional changes were decreased as the increasing of heat-treated time;Under 95% relative humidity,there were equilibrium moisture content of 23.6% for control group of poplar and 27.0% for radiata pine,after heat treatment for 24 h,they were decreased by 23.7% for poplar and 33.3% for radiata pine by reason of some water between hydroxyl bond in amorphous region of cellulose were taken off and come into being ether bond;after fitting of the equilibrium moisture content curve at different relative humidity over 0% to 95% relative humidity,the author can obtained the fiber saturation point of poplar and radiata pine which were control group,heat-treated for 8h and 24 h groups,they were 25.4%,21.5% and 18.7% for the former and 28.7%,25.6% and 18.8% for the latter respectively;the whole sorption time of poplar was increased by heat treatment during sorption run,and that of radiata pine was decreased;the hysteresis of poplar and radiata pine were weakened after heat treatment,and at the same condition,there was an obvious effect from heat-treated time on radiata pine;the relative humidity of highest point of hysteresis for controlled poplar and radiata pine both were 70%,and they were decreased to 65% for the former and 60% for the latter after heat treatment for 24h;Desorption process in same relative humidity at 40 ?,compared with control group,the unit mass heat absorption for first layer and multilayer bound water of heat-treated wood was less than that of the control group,it meant that the relationship between bound water and wood was less closer after heat treatment,hence bound water was more easier to lose;the unit mass heat absorption of first layer bound water was decreased after heat treatment,but that of multilayer bound water for radiata pine was increased compared to control group,it illustrated that the heat absorption of first layer bound water was decreased after heat treatment,and the decrease for the numbers of combined layers made an increase of heat absorption for multilayer bound water;to control group,the heat absorption for vaporization of multilayer bound water was increased with the increasing of moisture content,it accounted for increasing of unit mass heat absorption for multilayer bound water;the unit mass heat absorption of multilayer bound water for heat-treated poplar was greater at low moisture content than that at high moisture content compared to control group,it meant that the whole numbers of hydroxy for adsorbable water by wood were decreased after heat treatment,as a result of decrease for numbers of first layer bound water and the whole combined numbers of multilayer bound water;the heat for vaporization of multilayer bound water of poplar was more than that of radiata pine at low moisture content,it could be explained that the bond between bound water with poplar was more firm than that between bound water with radiate pine.