1 Anisotropic characteristics of wood dynamic viscoelastic properties Jianxiong Lu, Fucheng Bao and...

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


33

1. Introduction


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


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


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


R sample

r

l

t


35mm(R)×6mm(L)×1.5mm (T)


35mm(R)×12mm(L)×2.5mm (T)


T sample

t

l

r


35mm(T)×6mm(L)×1.5mm (R)


35mm(T)×12mm(L)×2.5mm (R)


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


constant temperature drying machine (DX-

400)

Heating

Treating temperature: 115oC

Treating time: 8h

Absolutely dried


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


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


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


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


3. Results & Discussion

3.1 Anisotropy in storage modulus E’


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)


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


3.2 Anisotropy in loss factor Tanδ


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


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


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


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


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


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


R sample

100

150

200

250

300

350

400

-150 -100 -50 0 50T(oC)

E'(M

Pa)

Virgin

Heat-treated

Freeze-treated




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


T sample

50

100

150

200

250

300

-150 -100 -50 0 50T(oC)

E'(M

Pa)

Virgin

Heat-treated

Freeze-treated




temperatures

Temperature dependences of E’ andTanδ for three kinds of T samplesmeasured by tension mode: α

β


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%)


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


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