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Abstract
The dynamic viscoelastic properties of Chinese fir (Cunninghamia lanceolata) with a moisture content of 10.65 % (30 °C, 58 % RH) under cyclical relative humidity (RH) variation (90–10 % RH) were examined. After seven-cycle RH changes, moisture content of specimens decreased. The storage modulus and loss factor increased and decreased, respectively. The occurrences of local maximum or minimum values of the storage modulus and loss factor lagged behind the occurrences of the maximum or minimum values of RH. Both lagged time and changing rate of storage modulus and loss factor decreased with the increasing cyclical times. When RH decreased from 90 to 10 % RH, the increasing rate of the storage modulus decreased with the decreasing of RH, while the loss factor decreased almost linearly. The unsteady effect and its partial recovery were observed during the desorption and the adsorption process, respectively. With the increasing cyclical times, the unsteady effect decreased and wood returned back to the dynamic equilibrium state gradually.
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1 State Key Laboratory of Tree Genetics and Breeding, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing, People’s Republic of China
2 State Key Laboratory of Tree Genetics and Breeding, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing, People’s Republic of China; Research Institute of Forestry New Technology, Chinese Academy of Forestry, Beijing, People’s Republic of China