| In this study,the growth ring of Catalpa bungei was taken as the research object.Realize the real-time and synchronous visualization studies on the adsorption/desorption isotherm and shrinkage/swelling behavior based on growth ring.Lead the study of wood shrinkage/swelling behavior from the macroscopic scale to the mesoscopic scale,which has important theoretical value and practical significance in understanding the nature of wood.Under the condition of 25? and 0(?)90%relative humidity,the Dynamic Vapor Sorption analysis with Dino X Lite Digital Microscope was used to carry out the real-time and synchronous visualization studies on the adsorption/desorption characteristics and shrinkage/swelling behavior of earlywood and latewood based on growth ring.The relationship of ongoing change between the moisture content and the shrinkage/swelling strain were determined,and so as to reveal the effect and mechanism of shrinkage/swelling law of earlywood and latewood,and their interaction modes on the shrinkage/swelling of growth ring.Explored the adsorption hysteresis,the strain hysteresis and the time hysteresis of earlywood and latewood.In this paper,the main conclusions were as follows:(1)The equilibrium moisture content of separated latewood was higher than separated earlywood under the any relative humidity level during the water adsorption stage(25°C,0?90%RH),and the differences between separated latewood and separated earlywood increased first and then reduced with the increase of relative humidity.The equilibrium moisture content of growth ring was somewhere in between separated latewood and separated earlywood.The performance of radial swelling dimensional change showed that: combined latewood(0.21-3.46%)? separated latewood(0.32-3.11%)> growth ring(0.23-3.02%)> combined earlywood(0.21-1.99%)? separated earlywood(0.28-1.98%).The radial swelling in combined latewood and combined earlywood promoted each other,and the radial swelling of the growth ring was up to the combined effect of them.The performance of tangential swelling showed that: combined latewood(0.23-4.84%)? separated latewood(0.38-4.72%)? growth ring(0.31-4.60%)?combined earlywood(0.24-4.54%)> separated earlywood(0.24-3.62%).The separated earlywood was the lowest and the combined earlywood was close to combined latewood,separated latewood and growth ring.The tangential swelling of growth ring was dominated by latewood.For the difference of swelling,the ratio of tangential to radial swelling in growth ring,combined latewood and separated latewood was 1.32,the ratio of tangential to radial swelling in separated earlywood and separated earlywood significantly increased when relative humidity greater than 40%.Among them,the separated earlywood increased to 1.83,combined earlywood to 2.28.Earlywood had a higher ratio of tangential to radial swelling than latewood.(2)The sequence of equilibrium moisture content from high to low was: growth ring,separated latewood,separated earlywood under the any relative humidity level during the water desorption stage(25°C,90%?0 RH),and the differences among them was decreased with the decrease of relative humidity.The performance of radial shrinkage dimensional change showed that: combined latewood(0.35-4.39%)? separated latewood(0.49-3.92%)> growth ring(0.38-3.92%)> separated earlywood(0.35-2.65%)? combined earlywood(0.34-2.60%).The negative shrinkage were observed in combined earlywood,and these negative shrinkage were compensated by positive shrinkage in latewood.The radial shrinkage of the growth ring was up to the combined effect of them.The performance of tangential shrinkage showed that: combined latewood(0.38-6.28%)> separated latewood(0.58-5.95%)> growth ring(0.52-5.97%)>combined earlywood(0.40-5.89%)> separated earlywood(0.40-4.50%).The separated earlywood was the lowest and the combined earlywood was close to combined latewood,separated latewood and growth ring.The tangential shrinkage of growth ring was dominated by latewood.For the difference of shrinkage,the ratio of tangential to radial shrinkage in growth ring,combined latewood and separated latewood was 1.33,the ratio of tangential to radial shrinkage in separated earlywood and separated earlywood significantly increased when relative humidity greater than 40%.Among them,the separated earlywood increased to 1.70,combined earlywood to 2.27.Earlywood had a higher ratio of tangential to radial shrinkage than latewood.(3)To reveal the sorption hysteresis in separated earlywood,separated latewood and growth ring,the "equilibrium moisture content during moisture adsorption" more than the "equilibrium moisture content during moisture desorption" under the same relative humidity level were used to make comparation and analysis.The results showed that the changes range of the sorption hysteresis ratio A/D were 0.59-0.84,0.66-0.79 and 0.60-0.77 in separated earlywood,separated latewood and growth ring,respectively.The sorption hysteresis difference ?W in separated earlywood,separated latewood and growth ring were 1.28-4.84%,1.10-4.50% and 1.32-5.55%,respectively.Indicating that sorption hysteresis appeared to be moderate with the increase of relative humidity and the sorption hysteresis in growth ring was affected by earlywood and latewood.(4)Compared the "swelling dimensional change during moisture adsorption" and "shrinkage dimensional changes during moisture desorption" under the same relative humidity level,we revealed that separated earlywood,separated latewood,combined earlywood,combined latewood and growth ring appeared hygro-expansion hysteresis that radial and tangential swelling dimensional change was lower than its shrinkage.The radial and tangential strain hysteresis ratio S/S(R)and S/S(T)were 0.55?0.79 and 0.59?0.77,respectively.The ranges of radial and tangential strain hysteresis difference ?R and ?T were 0.02?0.91 mm and0.06-0.72 mm,respectively.Among them,the radial strain hysteresis in separated earlywood showed a very jumble variation with the increase of relative humidity,and the rest of them increased with the increase of relative humidity,which suggesting that the strain hysteresis appeared to be moderate with the increase of relative humidity.The radial strain hysteresis in growth ring was up to the combined effect of earlywood and latewood.The tangential hygroexpansion hysteresis in growth ring was dominated by latewood.Moreover,compared with radial hygro-expansion hysteresis,the dependence of relative humidity within tangential hygroexpansion hysteresis was more similar with sorption hysteresis.(5)Under the same relative humidity,compared the data of "time point of equilibrium of moisture content" and "time point of equilibrium of shrinkage/swelling strain"."moisture content" and "shrinkage/swelling dimensional change" during the moisture adsorption and moisture desorption,were used to make comparation and performed the linear regression analysis.The results demonstrated that no time hysteresis appeared in separated earlywood,separated latewood and growth ring.The radial and tangential shrinkage/swelling strain at stage of constant equilibrium moisture content,were 4-orders of levels lower than which in processing of moisture adsorption and moisture desorption;radial and tangential shrinkage/swelling strains no more happened in growth ring,earlywood and latewood at stage of constant equilibrium moisture content.It meant that "equilibrium of moisture content" and "equilibrium of shrinkage/swelling strain" achieved synchronously. |
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