Influence of hygrothermal condition on dynamic viscoelasticity of Chinese fir (Cunninghamia lanceolata). Part 2: moisture desorption

Abstract

Abstract The influence of hygrothermal condition on dynamic viscoelasticity of Chinese fir (Cunninghamia lanceolata) during the moisture desorption (MDes) process was investigated. The ambient hygrothermal environments were set up as a series of constant temperatures and two relative humidity (RH) modes (RHramp-down and RHisohume). The MDes provided space for the rearrangement of the hydrogen bonds (Re-HB) and caused a mechano-sorptive (MS) effect. The enhancement of the Re-HB effect negatively correlated with the increment of loss modulus, while the elevation of the MS and the heating effects intensified the loss modulus. Lower values of RHc, determining the plateau area of loss modulus, were obtained at higher temperatures or greater RH ramping rates. The residual instability in the wood cell wall was quantitatively characterized by the extent of the MS effect. Residual instability was inversely proportional to the RHisohume level during the MDes process. The study of time dependent viscoelastic properties under moisture changing process provided insight into the condition of adsorbed water in the cell wall and optimized the manufacturing technique involved in the thermo-hygro-mechanical treatment of wood.