Anisotropic characteristics of wood dynamic viscoelastic properties

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
2
Materials Methods
Results Discussions
4
Conclusions
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
3
1. Introduction
Anisotropic of Chinese fir wood
Longitudinal Tracheids
(early- and latewood) Radial Tangential

Ray cells

• cell types
• cell arrangement

• Cross
• Radial
• Tangential

CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
4
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

CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
5
2. Materials Methods
2.1 Wood specimens

• 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

CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
6
Dimensions of specimens
L sample
For the tension tests 35mm(L)6mm(R)1.5mm
(T)
For the single cantilever bending tests
35mm(L)12mm(R)2.5mm (T)
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
7
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)
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
8
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)
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
9
2.2 Treatments
Freezing

• Pre- frost temperature - 29oC
• Condensation temperature - 49oC
• Sublimation vacuum degree 16.5Pa
• Treating time 25h
• Absolutely dried

Freeze-vacuum drying machine (FTS systems)
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
10
Heating

• Treating temperature 115oC
• Treating time 8h
• Absolutely dried

constant temperature drying machine (DX-400)
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
11
2.3 Conditioning
Saturated solution of Magnesium Chloride (MgCl2)
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
12
2.4 Measurements of the dynamic viscoelasticity
TA instruments DMA (Dynamic Mechanical
Analysis) 2980

• Temperature range-120 40oC
• Heating rate2oC/min
• Frequency1Hz
• Amplitude15um
• Tension flexural modes

CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
13
17.65mm (L/R/T)
17.65mm(L/R/T)
2.5mm (T/T/R)
Preload force
0.01N
6mm(R/L/L)
Sinusoidally varying strain
Sinusoidally varying strain
1Hz 15um
1Hz 15um
Single cantilever bending
Tension
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
14
2.5 E, E and Tand
Tand 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 Tand loss factor, a damping component, is
independent of a materials stiffness
E energy loss In internal motion
E elastic response
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
15
3. Results Discussion
3.1 Anisotropy in storage modulus E
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
16
Temperature dependences of E for L, R and T
samples measured by tension mode

• The E decreased with the
• increase of temperature

• 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

CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
17
Temperature dependences of E for L, R and T
samples measured by tension and single cantilever
bending modes

• E tension gt bending

L sample
R sample

• The most significant difference was
• found for L sample

T sample
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
18
3.2 Anisotropy in loss factor Tand
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
19
Temperature dependences of Tand for L, R and T
samples measured by tension mode

• a attributed to the glass
• transition of hemicellulose

ß
a

• ß due to the reorientation of
• methylol groups and adsorbed
• water molecules in amorphous
• of wood cell wall

• The intensity of transitions
• was highest for T sample

a

• Difference in loss peak
• temperatures

ß
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
20
Loss peak temperatures for L, R and T samples
measured by tension mode

• a L gtT gtR

• ß T gtR gt L

Conflicted with synthetic composites where
the higher loss Peak temperatures were found in
the stiffer direction
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
21
Temperature dependences of Tand for L, R and T
samples measured by tension and single cantilever
bending modes

• Tand tension lt bending

ß
a
L sample
a
ß
R sample

• Two relaxation processes

a
ß

• Difference in loss peak temperatures

T sample
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
22
Loss peak temperatures for L, R and T samples
measured by two mechanical modes

• Tension a L gtT gtR

ß T gtR gt L

• Bending a

ß T gtR gt L
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
23
3.3 Effect of freezing/heating treatments
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
24
L sample

• E heat gt virgin gt freeze

• Tand freeze gt virgin gt heat

• Difference in loss peak temperatures

Temperature dependences of E and Tand for three
kinds of L samples measured by tension mode
ß
a
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
25
R sample

• E heat gt virgin gt freeze

• Tand freeze gt virgin gt heat

• Difference in loss peak temperatures

Temperature dependences of E and Tand for three
kinds of R samples measured by tension mode
a
ß
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
26
T sample

• E heat gt virgin gt freeze

• Tand freeze gt virgin gt heat

• Difference in loss peak temperatures

Temperature dependences of E and Tand for three
kinds of T samples measured by tension mode
a
ß
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
27
Loss peak temperatures for virgin and treated
samples measured by tension mode

• Loss peak temperature Heating gt Virgin gt Freezing

• Due to their different equilibrium moisture
  content
• Heating (3.3) lt Virgin (4.8) lt Freezing
  (5.1)

CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
28
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 ß -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.
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY
29
Thank you for your attention
CHINESE RESEARCH INSTITUTE OF WOOD INDUSTRY