Effects Of Moisture Content On Dynamic Viscoelasticity Of Regenerated Lignocellulosic And Wood Materials

Lignocellulosic material is hydrophilic and viscoelastic.In order to clarify relationship between condition of water and dynamic viscoelasticity of lignocellulosic material,and its affected factors,such as chemical composition,condensed structure of cellulose and ultra-microscopic structure,two poplar trees which one of them is vertical and another is vertical.At one hand,the regenerated cellulose film and lignocellulosic film were coagulated after biorefinning and dissolving in ionic liquid.At another hand,fresh tension wood from inclined tree was separated along with fresh normal wood from vertical tree.And then,they were regulated to three different types of specimen,including sample with different drying time,sample with different equilibrium moisture content(EMC)both by desorption and sorption.DSC,XRD and DMA tests were implemented on those samples.The conclusion were listed as follows:Quantity of absorbing water both of regenerated cellulose and lignocellulosic film was increased with the exterior relative humidity.The regenerated films with high moisture content have two exothermic peaks in cooling period of DSC test,while other films with low water content have no obvious transmitting of enthalpy.It was suggested that the first exothermic peak was formed by heterogeneous crystallization of free water while the second one was due to crystallization of multilayer absorbing water in amorphous area of films.The cellulose polymorph of regenerated film is type II,and 2? peak position of XRD pattern is independent to moisture content.It means crystalline structure of cellulose couldn't be altered by swelling of water.However,the width of half maximum height of 2? peak were changing with moisture content randomly.DMA test had revealed one relaxation peaks at temperature range of-150 Co to 50 Co.The peak known as ? relaxation was moved into low temperature when moisture content was increasing in regenerated cellulose films sample.Nevertheless,in lignocellulosic films,the peak backward to low temperature at first,and then keep fluctuating in a narrow range.Therefore,it was suggested that the rotating movement of methylol groups was improved by absorbing of water at amorphous area,and water acting as plasticizer here.The moisture content both of normal wood and tension wood samples was decreasing with the drying time.There are two separated exothermic peaks were found at cooling period of DSC curve at fresh normal wood and tension wood.When after drying seven days,the two peaks moving to low temperature and after 14 daysthe peaks was required.Both in process of desorption and absorption,the equilibrium moisture content of wood specimen were increasing with exterior relative humidity.Difference of EMC between normal wood and tension wood is small in desorption process,while normal wood had higher EMC than tension wood in absorption process.When comparing EMC of desorption with sorption at the same exterior relative humidity,sorption hysteresis was detected at atmosphere of 33%RH and 77%RH.No endothermic and exothermic peak was found at DSC curve both normal wood and tension wood sample which prepared by desorption with sorption process.It was deduced that there are no apparent phase transition of bound water in this samples.MFA of tension wood is lower than normal wood,and MFA of both samples is independent to moisture content.CrI of tension wood was continuously declining with decreasing EMC,and that of normal decreased at first and increased later.DMA test was set for clarify dynamic viscoelasticity both of tension wood and normal wood in the desorption process.In the temperature range of-150 Coto 50 Co,two separated relaxation peaks were detected which was designed as ? and ? respectively.The position of two peaks moved into low temperature generally when EMC of wood sample was increasing.However,when it comes to sorption process,the moving direction of peak relied on level of moisture content.Only when moisture content of tension wood among 0.8%-7.6% and normal wood among 0.8%-9.6%,the? relaxation peak could be found and it transferred into lower temperature along with increasing moisture content.Meanwhile,the total ? relaxation peak would appear only at wood samples with high water content and it also step forward low temperature along with increasing water content.