1 Anisotropic characteristics of wood dynamic viscoelastic properties Jianxiong Lu, Fucheng Bao and Jiali Jiang Key Laboratory of Wood Science and Technology of State Forestry Administration Research Institute of Wood Industry Chinese Academy of Forestry CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY

2 Outline Introduction 1 Materials & Methods 2 3 Conclusions 4 Results & Discussions CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY

3 1. Introduction CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 1Cross 2Radial 3Tangential Anisotropic of Chinese fir wood Longitudinal Tracheids (early- and latewood) Radial Tangential Ray cells cell types cell arrangement

4 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY Aim & scope Dynamic mechanical properties of wood in the longitudinal, radial and tangential directions Dynamic mechanical behaviors under tension and flexural modes The effects of freezing and heating treatments

5 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 2. Materials & Methods Chinese fir （ Cunninghamia lanceolata ） heartwood The initial moisture content was about 82% The average basic density was 0.27g/cm 3 Specimens were selected without knots and defects 2.1 Wood specimens

6 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY Dimensions of specimens For the single cantilever bending tests: 35mm(L)×12mm(R)×2.5mm (T) For the tension tests: 35mm(L)×6mm(R)×1.5mm (T) L sample

7 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY R sample For the tension tests: 35mm(R)×6mm(L)×1.5mm (T) For the single cantilever bending tests: 35mm(R)×12mm(L)×2.5mm (T)

8 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY T sample For the tension tests: 35mm(T)×6mm(L)×1.5mm (R) For the single cantilever bending tests: 35mm(T)×12mm(L)×2.5mm (R)

9 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 2.2 Treatments Freezing Freeze-vacuum drying machine (FTS systems) Pre- frost temperature: - 29 o C Condensation temperature: - 49 o C Sublimation vacuum degree: 16.5Pa Treating time: 25h Absolutely dried

10 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY constant temperature drying machine (DX-400) Heating Treating temperature: 115 o C Treating time: 8h Absolutely dried

11 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 2.3 Conditioning Saturated solution of Magnesium Chloride (MgCl 2 ) Temperature 22 o C R.H. (%) E.M.C (%) Virgin Freezing Heating

12 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 2.4 Measurements of the dynamic viscoelasticity TA instruments® DMA (Dynamic Mechanical Analysis) 2980 Temperature range ： -120 ~ 40 o C Heating rate ： 2 o C/min Frequency ： 1Hz Amplitude:15um Tension & flexural modes

13 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY Preload force 17.65mm(L/R/T) 6mm(R/L/L) 1Hz 15um 0.01N Sinusoidally varying strain 17.65mm (L/R/T) 2.5mm (T/T/R) Single cantilever bending 1Hz 15um Tension Sinusoidally varying strain

14 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 2.5 E’, E’’ and Tanδ Tanδ= E’’/ E’ E’: storage modulus, an elastic part, is a measure of the energy stored elastically E’’ : loss modulus, a damping component, is a measure of the energy lost as heat Tanδ: loss factor, a damping component, is independent of a material’s stiffness E’~ elastic response E’’~ energy loss In internal motion

15 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 3. Results & Discussion 3.1 Anisotropy in storage modulus E’

16 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY The E’ decreased with the increase of temperature Temperature dependences of E’ for L, R and T samples measured by tension mode : The E’ was much lower in the transverse than in the longitudinal direction the E’ in the radial was some 60% higher than that in tangential direction

17 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY L sample R sample T sample Temperature dependences of E’ for L, R and T samples measured by tension and single cantilever bending modes: E’ : tension ＞ bending The most significant difference was found for L sample

18 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 3.2 Anisotropy in loss factor Tanδ

19 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY α: attributed to the glass transition of hemicellulose Temperature dependences of Tanδ for L, R and T samples measured by tension mode : The intensity of transitions was highest for T sample β: due to the reorientation of methylol groups and adsorbed water molecules in amorphous of wood cell wall β α α β Difference in loss peak temperatures

20 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY α ( o C)β ( o C) LRTLRT Loss peak temperatures for L, R and T samples measured by tension mode α: L ＞ T ＞ R β: T ＞ R ＞ L Conflicted with synthetic composites where the higher loss Peak temperatures were found in the stiffer direction

21 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY L sample R sample T sample Temperature dependences of Tanδ for L, R and T samples measured by tension and single cantilever bending modes : Two relaxation processes Difference in loss peak temperatures α α α β β β Tanδ: tension ＜ bending

22 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY α ( o C)β ( o C) LRTLRT Tension Bending Loss peak temperatures for L, R and T samples measured by two mechanical modes Tension α: L ＞ T ＞ Rβ: T ＞ R ＞ L Bending α&β: T ＞ R ＞ L

23 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 3.3 Effect of freezing/heating treatments

24 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY L sample Tanδ: freeze ＞ virgin ＞ heat E’ : heat ＞ virgin ＞ freeze Difference in loss peak temperatures Temperature dependences of E’ and Tanδ for three kinds of L samples measured by tension mode: α β

25 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY R sample Tanδ: freeze ＞ virgin ＞ heat E’ : heat ＞ virgin ＞ freeze Difference in loss peak temperatures Temperature dependences of E’ and Tanδ for three kinds of R samples measured by tension mode: α β

26 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY T sample Tanδ: freeze ＞ virgin ＞ heat E’ : heat ＞ virgin ＞ freeze Difference in loss peak temperatures Temperature dependences of E’ and Tanδ for three kinds of T samples measured by tension mode: α β

27 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY α ( o C)β ( o C) LRTLRT Virgin Heating Freezing 36.1 ＞ Loss peak temperatures for virgin and treated samples measured by tension mode Loss peak temperature: Heating ＞ Virgin ＞ Freezing Due to their different equilibrium moisture content: Heating (3.3%) ＜ Virgin (4.8%) ＜ Freezing (5.1%)

28 CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY 4. Conclusions 1) The specimens oriented parallel to the grain presented the highest storage modulus E’, and the E’ was much lower in the tangential direction than in the radial direction; 2) The L sample showed a lower β -loss peak temperature than that for the R and T samples, which was in conflict with polymer composites where the higher loss peak temperatures were found in the stiffer direction; 3) The rheological properties of wood showed a dependence upon the mechanical modes used during experiments. Tension mode presented higher stiffness than the flexural mode; 4) The dynamic viscoelastic behavior of wood was affected by freezing or heating treatment.

29 Thank you for your attention CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY