Viscoelastic Properties of the Chinese Fir (Cunninghamia lanceolata) during Moisture Sorption Processes Determined by Harmonic Tests

Tianyi Zhan; Jianxiong Lu; Jiali Jiang; Hui Peng; Anxin Li; Jianmin Chang

doi:10.3390/ma9121020

Viscoelastic Properties of the Chinese Fir (Cunninghamia lanceolata) during Moisture Sorption Processes Determined by Harmonic Tests

Materials (Basel). 2016 Dec 17;9(12):1020. doi: 10.3390/ma9121020.

Authors

Tianyi Zhan^{1

2}, Jianxiong Lu³, Jiali Jiang⁴, Hui Peng⁵, Anxin Li⁶, Jianmin Chang⁷

Affiliations

¹ State Key Laboratory of Tree Genetics and Breeding, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China. tyzhan@njfu.edu.cn.
² College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, China. tyzhan@njfu.edu.cn.
³ State Key Laboratory of Tree Genetics and Breeding, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China. jianxiong@caf.ac.cn.
⁴ State Key Laboratory of Tree Genetics and Breeding, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China. jialiwood@caf.ac.cn.
⁵ State Key Laboratory of Tree Genetics and Breeding, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China. penghyx@126.com.
⁶ State Key Laboratory of Tree Genetics and Breeding, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China. lianxin6928@126.com.
⁷ College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China. cjianmin@bjfu.edu.cn.

Abstract

Measured by harmonic tests, the viscoelastic properties of Chinese fir during moisture sorption processes were examined under three relative humidity (RH) modes: RH_ramp, RH_isohume, and RH_step. The stiffness decreased and damping increased as a function of the moisture content (MC), which is presumed to be the effect of plasticization and an unstable state. The increasing damping was associated with the breaking of hydrogen bonds and the formation of free volume within polymer networks. The changes of loss modulus ratio at 1 and 20 Hz, E″_1Hz/E″_20Hz, proved the changing trend of the unstable state. Higher ramping rates aggravated the unstable state at the RH_ramp period, and higher constant RH levels provided more recovery of the unstable state at the RH_isohume period. Changes of viscoelastic properties were associated with RH (varied or remained constant), and the application of Boltzmann's superposition principle is a good approach to simulate viscoelasticity development.

Keywords: Chinese fir; harmonic test; mode of RH increment; plasticization effect; sorption; unstable state; viscoelasticity.