Effects of thermal treatment temperature and duration on mass loss and rupture modulus of Cunninghamia lanceolata

  Objective  Heat treatment can improve the dimensional stability of wood, but it will simultaneously reduce its mass and affect its mechanical properties. So it is necessary to explore the mechanism of heat treatment on wood mass and mechanical properties.

  Method  In this study, flakes of Chinese fir plantation were used as the test material, and they were treated at 160, 180, 200, 220 °C and nitrogen atmosphere for 1, 2, 3, 4, 5 and 6 hours, respectively. The mass loss rate (m_L) and static bending strength (MOR) of treated wood were tested, characterized by ATR-FTIR and TGA. And the prediction model of mass loss and MOR during heat treating process was established.

  Result  When the heat treating temperature didn’t exceed 200 ℃, it had a more significant impact on the mass loss and mechanical properties of wood than the heat treating time. When the heat treating temperature exceeded 200 °C, heat treating temperature and time had significant effects on wood mass loss and mechanical properties. The mass loss rate of Chinese fir wood showed a non-linear increase with the increase of heat treating temperature and heat treating time, and when the range of mass loss rate was between 0.2% and 17.6%, a model can be established, lnm_L = 0.8 lnt + 9.35 lnT – 53.67 (t is time, T is temperature), R² was 0.99. And the tested values were basically consistent with the predicted values. The MOR of Chinese fir wood decreased linearly with the increase of heat treating temperature and heat treating time. Compared with untreated wood, MOR decreased by 4.4%−74.8%, and a model which had a better forecast can be established, MOR = −2.57t – 0.82T + 220.44, R² was 0.93. The MOR of heat-treated wood decreased exponentially with the increase of mass loss, and a model that accurately predict the changing trend of MOR with mass loss can be established, MOR = 65.4\rme^ - 20m_\rmL + 16.4, R² was 0.95.

  Conclusion  This study establishes the empirical equations between mass loss and the heat treating conditions, the MOR and the heat conditions, the mass loss and MOR of Chinese fir wood through the experimental data, which can provide reference and basis for optimization of wood heat treating process and prediction of heat-treated wood performance.