Study On The Effect Of High Pressure On Moisture Sorption Properties Of Paulownia Wood

With the development of the protection awareness of natural forest resources,the fast-growing forest timber in its place has attracted more and more attention because of its abundant domestic production.High pressure technology is a new wood modification technology.It has been proved in some studies,the hardness,density and other performance indexes of poplar,Chinese fir and paulownia can be obviously improved by high pressure treatment.Based on the conclusion,the research on the storage stability of high pressure treated paulownia wood in the later period,especially the influence of moisture content factor which is closely related to the storage stability on the product,has not been carried out in the past research.Therefore in this paper,characteristics like moisture sorption and desorption,microstructure and composition of high pressure treated paulownia wood will be studied.Microstructure analysis will be carried out using Scanning Electronic Microscopy?SEM?.The effect of high pressure parameters?pressure and holding time?,environmental temperature and relative humidity on moisture sorption property of paulownia wood will be studied.Nondestructive technology will be introduced to study the key structures like hygroscopic group structure and chemical bound.Moisture distribution in high pressure treated paulownia wood will be analyzed by using the nuclear magnetic resonance?NMR?.Mathemetical models will be established based on MSI curve and thermodynamic analysis will be combined for studying the moisture characteristics and energy changes in paulownia wood.The high pressure treatment pressure levels are 30,90,150MPa,the holding times are 3,30,300s.Results are as follows:1.High pressure treatment can change the EMC of paulownia wood under different ambient humidity.Different pressure and holding time levels have influence on the EMC of paulownia wood.The higher and longer the pressure and treatment time are,the higher the environmental humidity is,making the sorption difference between the control and treated paulownia wood more obvious.Under high humidity conditions,the treated paulownia has higher moisture content while in the low humidity range,the EMC of high pressure treated paulownia is lower than that of untreated paulownia.2.Moisture content of high pressure treated paulownia wood goes down with the rise of temperature,and the temperature effect on treated paulownia is less obvious than untreated paulownia.The MSI curve of each group belongs to type?isotherm.Hygroscopic hysteresis exists in high pressure trated paulownia wood.The hygroscopic hysteresis ring area of paulownia wood in the control group was smaller than that in all the high pressure treated groups.3.As the processing pressure increases,the porosity decreases,the degree of communication between micropores decreases,and then the permeability also decreases.Together with the effect of unbound adsorption on the structure of wood fiber,the stoppage effect of the collapse of the catheter explained reason that the permeability of paulownia wood did not increase or decrease uniformly after treatment,compared with the control group.4.High pressure treatment reduced the amount of hydroxyl and carbonyl groups slightly in paulownia wood thus reduced the hygroscopicity of paulownia wood in this aspect.5.The change of water content of high pressure paulownia wood is mainly caused by the changing of bound water,which related to the swelling and shrinkage,thus making the dimension of paulownia wood unstable.6.Modified Henderson is the best fitting model.Thermodynamic analysis revealed that at low moisture content,high pressure treated paulownia wood has high q_st and?S.According to the entropy-enthalpy complementary theory,the water adsorption process is non-spontaneous and the desorption process is spontaneous.The adsorption and desorption processes are both driven by enthalpy.