Study On Dynamic Water Vapour Sorption Properties And Pore Characteristics Of Two Species Of Wood

Pinus Tableuliformis Carr.and Populus davidiana Dode were used as the research object,and Dynamic vapour sorption technology was used to measure the data of samples of different sizes.The Hailwood-Horrobin model and the Parallel Exponential Kinetics model was used to analyze the data;The sorption data was used to analyze the pore size distribution of wood by Barrett-Joyner-Halenda model.Dubinin-Radushkevich model was used to calculate the micropore volume of wood,and analyzed the influence of temperature on the pores.The purpose was to explore the possibility of studying the pore characteristics of wood by DVS method;The same samples were also tested by nitrogen sorption method.The parameters such as specific surface area,pore size distribution and pore volume were compared with those obtained by DVS method.The conclusions were as follows:The DVS test found that the adsorption moisture content of the samples steppedly increased as the humidity increased.At each adsorption stage,the moisture content of the samples increased rapidly in the beginning and then slowly increased to equilibrium.In the desorption stage,the moisture content of the samples steppedly decreased as the humidity decreased.At each desorption stage,the moisture content of the samples decreased rapidly in the beginning and then slowly decreased to equilibrium.The higher the temperature was,the lower the hysteresis difference of the sample was.The temperature helped to inhibit the hysteresis of the wood.At the same conditions,the moisture content of Populus davidiana Dode samples were always greater than the moisture content of the Pinus Tableuliformis Carr.samples;At the same condition,when the particle size was 0.45-0.63mm,the moisture content was highest.The model study found that the Hailwood-Horrobin model was suiTablele for the sorption process of Pinus Tableuliformis Carr.and Populus davidiana Dode,and could accurately fit the moisture content data of each humidity stage.The R²is higher than 0.900.The values of parameters A,B,and C were approach to the data studied by J Zaihan.The W value of the samples increased as the temperature increased,indicating that the higher the temperature was,the weaker the sorption properties was.At the same conditions,the W value of the 0.45-0.63mm samples were the lowest;According to Hailwood-Horrobin model study,monolayer adsorption moisture content increased rapidly and then slowly increased until the final equilibrium,the multilayer moisture content slowly increased in the beginning and then increased rapidly to the end.The PEK model could accurately fit the moisture content data of each humidity stage,and R² was above 0.990.During the sorption process,the fast moisture content MC₁ increased rapidly in the beginning and slowly increased until equilibrium,and the slow moisture content MC₂increased slowly in the beginning and rapidly increased to the end of the process.The slow time t₂ was always longer than the corresponding fast time t₁,and t₁ and t₂ increased as the relative humidity increased.The fast and slow moisture content in the desorption stage were always greater than the fast and slow moisture content of the corresponding adsorption stage.At the same condition,it was found that both the fast and slow moisture content of the samples decreased with increasing temperature.The DVS method was used to study the pore characteristics of wood.The pores in the samples were mainly distributed in the range of 2-5nm.The average rate of the mesopore volume in 2-5nm was 84.20%,8.27%in 5-20nm,7.52%in 20-40nm;The temperature was linearly negatively correlated with the pore volume,the R² was above 0.900,as the temperature increased,the moisture content of the wood decreased.Nitrogen sorption method found that the nitrogen sorption isotherms of Pinus Tableuliformis Carr.and Populus davidiana Dode were the mixed isotherms of II and IV.The volume adsorbed increased as relative pressure increased.The hysteresis was H3 hysteresis;The pore volume in the samples decreased as pore size increased;The pores in the samples were mainly distributed in the range of 2-5nm;At the same conditions,the volume adsorbed of the Populus davidiana Dode was higher than that of Pinus Tableuliformis Carr..Compared the DVS method with the nitrogen sorption method,we found that the mesopores of the two species were mainly distributed in the range of 2-5nm.H₂O molecules were more likely to enter smaller pore sizes than N₂ molecules,so the rate of the mesopore volume in the 2-5nm of DVS method were higher than Nitrogen sorption method.Compared with the nitrogen sorption method,the pore volume calculated by the DVS method was smaller.Probably because the two models did not exactly match the DVS test data,which affected the accuracy of the DVS method for measuring the pore data.