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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
22
Outline
Introduction 1
Materials & Methods2
3
Conclusions4
Results & Discussions
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
33
1. Introduction
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
1 Cross
2 Radial
3 Tangential
Anisotropic of Chinese fir wood
Longitudinal Tracheids
(early- and latewood)
Radial
Tangential Ray cells
cell types
cell arrangement
44CHINESE 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
55CHINESE 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/cm3
Specimens were selected without knots and defects
2.1 Wood specimens
66CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
l
r
t
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
77CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
R sample
r
l
t
For the tension tests:
35mm(R)×6mm(L)×1.5mm (T)
For the single cantilever bending tests:
35mm(R)×12mm(L)×2.5mm (T)
88CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
T sample
t
l
r
For the tension tests:
35mm(T)×6mm(L)×1.5mm (R)
For the single cantilever bending tests:
35mm(T)×12mm(L)×2.5mm (R)
99CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
2.2 Treatments
Freezing
Freeze-vacuum drying machine (FTS systems)
Pre- frost temperature: - 29oC
Condensation temperature: - 49oC
Sublimation vacuum degree: 16.5Pa
Treating time: 25h
Absolutely dried
1010CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
constant temperature drying machine (DX-
400)
Heating
Treating temperature: 115oC
Treating time: 8h
Absolutely dried
1111CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
2.3 Conditioning
Saturated solution of Magnesium Chloride (MgCl2)
Temperature 22oC
R.H. (%) E.M.C (%)
Virgin Freezing Heating
33 4.8 5.1 3.3
1212CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
2.4 Measurements of the dynamic viscoelasticity
TA instruments®
DMA (Dynamic Mechanical Analysis) 2980
Temperature range : -120 ~ 40oC
Heating rate : 2oC/min
Frequency : 1Hz
Amplitude:15um
Tension & flexural modes
1313CHINESE 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
1414CHINESE 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
1515CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
3. Results & Discussion
3.1 Anisotropy in storage modulus E’
1616CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
9
10
11
12
13
-150 -100 -50 0 50T(oC)
E'(G
Pa)
L sample
100
150
200
250
300
350
-150 -100 -50 0 50T(oC)
E'(M
Pa)
R sample
T sample
The E’ decreased with the
increase of temperature
Temperature dependences of E’ for L,R and T samples measured by tensionmode :
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
1717
80
100
120
140
160
180
200
220
-150 -100 -50 0 50T(oC)
E'(M
Pa)
100
150
200
250
300
350
-150 -100 -50 0 50T(oC)
E'(M
Pa)
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
2
4
6
8
10
12
14
-150 -100 -50 0 50T(oC)
E'(G
Pa)
Tension
Bending
L sample
R sample
T sample
Temperature dependences of E’ for L, R andT samples measured by tension and singlecantilever bending modes:
E’ : tension > bending
The most significant difference was
found for L sample
1818CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
3.2 Anisotropy in loss factor Tanδ
1919CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
0.005
0.010
0.015
0.020
0.025
-150 -100 -50 0 50T(oC)
Tan
δL sample
0.01
0.02
0.03
0.04
0.05
0.06
0.07
-150 -100 -50 0 50T(oC)
Tan
δ
R sample
T sample
α: attributed to the glass
transition of hemicellulose
Temperature dependences of Tanδ for L,R and T samples measured by tensionmode :
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
0.005
0.010
0.015
0.020
0.025
-150 -100 -50 0 50T(oC)
Tan
δL sample
βα
α
β Difference in loss peak
temperatures
2020CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
α (oC) β (oC)
L R T L R T
36.1 26.2 30.7 -93.2 -90.4 -87.1
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
2121
0.02
0.03
0.04
0.05
0.06
0.07
-150 -100 -50 0 50T(oC)
Tan
δ
0.01
0.02
0.03
0.04
0.05
0.06
0.07
-150 -100 -50 0 50T(oC)
Tan
δ
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
0.005
0.015
0.025
0.035
0.045
-150 -100 -50 0 50T(oC)
Tan
δTension
Bending
L sample
R sample
T sample
Temperature dependences of Tanδ for L, R and T samples measured by tension andsingle cantilever bending modes :
Two relaxation processes
Difference in loss peak temperatures
α
α
α
β
β
β
Tanδ: tension < bending
2222CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
α (oC) β (oC)
L R T L R T
Tension
Bending
36.1
2.6
26.2
30.3
30.7
36.1
-93.2
-95.8
-90.4
-93.0
-87.1
-90.7
Loss peak temperatures for L, R and T samples
measured by two mechanical modes
Tension α: L > T > R β: T > R > L
Bending α&β: T > R > L
2323CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
3.3 Effect of freezing/heating treatments
2424
0.005
0.010
0.015
0.020
0.025
-150 -100 -50 0 50T(oC)
Tan
δ
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
L sample
7
8
9
10
11
12
13
14
-150 -100 -50 0 50T(oC)
E'(G
Pa)
Virgin
Heat-treated
Freeze-treated
Tanδ: freeze > virgin > heat
E’ : heat > virgin > freeze
Difference in loss peak
temperatures
Temperature dependences of E’ andTanδ for three kinds of L samplesmeasured by tension mode:
αβ
2525
0.01
0.02
0.03
0.04
0.05
0.06
-150 -100 -50 0 50T(oC)
Tan
δ
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
R sample
100
150
200
250
300
350
400
-150 -100 -50 0 50T(oC)
E'(M
Pa)
Virgin
Heat-treated
Freeze-treated
Tanδ: freeze > virgin > heat
E’ : heat > virgin > freeze
Difference in loss peak
temperatures
Temperature dependences of E’ andTanδ for three kinds of R samplesmeasured by tension mode: α
β
2626
0.015
0.025
0.035
0.045
0.055
0.065
0.075
-150 -100 -50 0 50T(oC)
Tan
δ
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
T sample
50
100
150
200
250
300
-150 -100 -50 0 50T(oC)
E'(M
Pa)
Virgin
Heat-treated
Freeze-treated
Tanδ: freeze > virgin > heat
E’ : heat > virgin > freeze
Difference in loss peak
temperatures
Temperature dependences of E’ andTanδ for three kinds of T samplesmeasured by tension mode: α
β
2727CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
α (oC) β (oC)
L R T L R T
Virgin
Heating
Freezing
36.1
> 40
31.7
26.2
31.5
23.4
30.7
34.9
26.7
- 93.2
- 88.6
- 97.7
- 90.4
- 85.1
- 93.7
- 87.1
- 82.8
- 91.4
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%)
2828CHINESE 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.
2929
Thank you for your attention
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY