Evidence of mechano-sorptive effect during moisture adsorption process under hygrothermal conditions: Characterized by static and dynamic loadings

• Wood viscoelasticity were examined during adsorption processes under hygrothermal conditions.
• Comparison of viscoelasticity under static and dynamic loadings was investigated.
• Mechano-sorptive effect could be detected under dynamic loading.
• Mechano-sorptive effect was more pronounced at varied humidity than constant.

The viscoelasticity of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) was examined during moisture adsorption at a relative humidity step (RHstep) mode (made up of RHramp and RHisohume periods) from 0 to 90% RH and temperatures ranging from 30 to 80 °C. The viscoelastic tests were carried out by static and dynamic loadings. The moisture adsorption resulted in an increase in compliance or damping. The phenomena that more pronounced mechano-sorptive (MS) effect during RHramp periods than RHisohume periods were observed, indicating that the MS effect could be detected by both static and dynamic loading tests. At 70 or 80 °C dynamic loading tests, the lignin transition was observed. Before the occurrence of the lignin transition, or when temperature at or below 60 °C, a smooth master curve of E″ vs. E′ was formed and indicated that during the adsorption process the temperature not only accelerated the viscoelastic processes, but also increased their intensity.