Study on the moisture-induced swelling/shrinkage and hysteresis of Catalpa bungei wood across the growth ring

Abstract

Abstract The moisture adsorption/desorption and swelling/shrinkage behavior of Catalpa bungei wood samples were documented in real-time at a mesoscopic scale using dynamic vapor sorption resolution combined with a Dino X Lite Digital Microscope. The results showed that earlywood, latewood, and growth ring samples exhibited varying water vapor sorption isotherms and hysteresis degrees throughout all relative humidity (RH) levels. The radial swelling/shrinkage strains in the separated earlywood (EW) and the growth ring earlywood (GR-E) were lower than that in separated latewood (LW) and growth ring latewood (GR-L) regions. The growth ring region (GR) containing earlywood and latewood tissues , presented an intermediate strain behavior. In contrast, GR-E’s swelling/shrinkage strains resemble LW, GR-L, and GR in the tangential direction. In particular, the GR swelling/shrinkage behavior resembled that of latewood regions, and GR-L had maximum swelling/shrinkage strains. This means that latewood dominated the swelling/shrinkage of the growth ring, promoted to a certain extent by earlywood. Strain hysteresis was observed when the swelling/shrinkage strain was considered an RH function. Latewood regions (LW, GR-L) showed more pronounced swelling hysteresis than earlywood regions (EW, GR-E) in the tangential and radial directions. Furthermore, at any relative humidity the change of the size of the specimen was immediately stabilized when the moisture content reached its equilibrium.