Influence of wood structure on Influence of wood structure on moisture moisture desorptiondesorption and changes and changes in its properties above the fiber in its properties above the fiber

saturation pointsaturation point

Giana Almeida, Ph.D. Student

Roger Hernández, Professor

SWST 48SWST 48thth Annual ConventionAnnual Convention

Québec City, June 2005

PlanPlan

ObjectivesObjectivesDefinitionsDefinitionsMaterial and MethodsMaterial and MethodsResultsResultsConclusionsConclusions

Influence of wood structure on boundary Influence of wood structure on boundary moisture moisture desorptiondesorption..

Changes in wood properties above the Changes in wood properties above the FSP (influence of wood structure on these FSP (influence of wood structure on these changes).changes).

ObjectivesObjectives

Boundary Boundary desorptiondesorption

DefinitionsDefinitions

–– Water potential (Water potential (ΨΨ)): water : water in a medium is characterized in a medium is characterized in terms of its energy statein terms of its energy state

–– MC x MC x ΨΨ : region between 96% : region between 96% and 100% RH is spread out and 100% RH is spread out (wood structure highly affects (wood structure highly affects the drainage curve in this the drainage curve in this region)region)

• Adsorption

Water potential Ψ(Jkg-1)

EMC

(%

)

Desorption

EMC-water potential relationship of western hemlock sapwood at 21°C (Fortin 1979).

–– Affects the MCAffects the MC--water water relationship (at high MC relationship (at high MC values values –– capillary forces)capillary forces)

Desorption

Adsorption

DefinitionsDefinitions

–– Capillary system of wood → cavities Capillary system of wood → cavities interconnected by narrow channelsinterconnected by narrow channels

Ink bottle effectInk bottle effect• Adsorption

Water potential Ψ(Jkg-1)EM

C (

%)

Desorption

EMC-water potential relationship of western hemlock sapwood at 21°C (Fortin 1979).

Fiber saturation point (FSP)Fiber saturation point (FSP)

“Moisture content (MC) at which the cell walls “Moisture content (MC) at which the cell walls are saturated with bound water with no free are saturated with bound water with no free water in the cell cavities (water in the cell cavities (TiemannTiemann 1906).”1906).”

“FSP is the MC below which the physical and “FSP is the MC below which the physical and mechanical properties of wood begin to change mechanical properties of wood begin to change

as a function of MC (USDA 1974).”as a function of MC (USDA 1974).”

DefinitionsDefinitions

DefinitionsDefinitions

Fiber saturation point (FSP)Fiber saturation point (FSP)

““Shrinkage in beech begins to take place Shrinkage in beech begins to take place above the FSP (Stevens 1963).” above the FSP (Stevens 1963).”

““Bound and free water appear to coexist Bound and free water appear to coexist over a significant range of water potentials over a significant range of water potentials -- above and below the FSP (above and below the FSP (SiauSiau 1995).”1995).”

MaterialMaterial

Yellow birch (Yellow birch (BetulaBetula alleghaniensisalleghaniensis))Sugar maple (Sugar maple (Acer Acer saccharumsaccharum))

American beech (American beech (FagusFagus grandifoliagrandifolia))

(T)

60 m

m

20 m

m

(R)20 mm(L)

Sorption and physical-mechanical

tests

10 mm

10 m

m

3 mm

(T)

(R)

(L)

Mercury porosimetry Anatomical analysis

TR: 10mm x 10mm x 20µm

TL: 10mm x 10mm x 30µm

MaterialMaterial

Anatomical analysisAnatomical analysis–– MicrosectionsMicrosections were double stainedwere double stained–– Image treatment (Image treatment (MicromorphMicromorph))–– Quantitative anatomical analysis (Quantitative anatomical analysis (WinCellWinCell))

Beech – TR original image Beech – treated image

MethodsMethods

Moisture sorption testsMoisture sorption tests

–– Full saturation under distilled waterFull saturation under distilled water–– One condition in adsorption above distilled waterOne condition in adsorption above distilled water–– Five Five desorptiondesorption conditions using pressure membrane conditions using pressure membrane

method (RHmethod (RH>96%)>96%)–– Five Five desorptiondesorption conditions using saturated salt conditions using saturated salt

solutions (33% ≤ RH ≤ 90%)solutions (33% ≤ RH ≤ 90%)

Moisture sorption testsMoisture sorption tests

Shrinkage and mechanical tests at EMCShrinkage and mechanical tests at EMC

Quantitative anatomical analysisQuantitative anatomical analysis

Mercury porosimetry analysisMercury porosimetry analysis

MethodsMethods

0

20

40

60

80

100

0.001 0.01 0.1 1 10 100 1000

Pore radius (µm)

Cum

ulat

ive

void

vol

ume

(%)

10-3 10-2 10-1 100 101 102 103

–– MicromeriticsMicromeritics AutoPoreAutoPore IV SeriesIV SeriesLow pressure Low pressure –– 0 to 50 0 to 50 psipsi ((pore radius from 180 pore radius from 180 µµm to 1.8 m to 1.8 µµm)m)

High pressure High pressure –– AP to 60,000 AP to 60,000 psipsi (pore radius until 0.0015 (pore radius until 0.0015 µµm)m)

Mercury porosimetry analysisMercury porosimetry analysis

Cumulative void volume of yellow birch obtained by mercury porosCumulative void volume of yellow birch obtained by mercury porosimetry analysis.imetry analysis.

MethodsMethods

0

20

40

60

80

100

120

1101001000100001000001000000

Water potential Ψ (Jkg-1)

EM

C (%

)

yellow birch

-106 -105 -104 -103 -102 -101 -100

1

Equilibrium moisture contentEquilibrium moisture content--water potential relationship at 25water potential relationship at 25°°C (yellow birch and C (yellow birch and beech) and at 20beech) and at 20--2121°°C (sugar maple, C (sugar maple, HernándezHernández and and BizoňBizoň 1994).1994).

0

20

40

60

80

100

120

1101001000100001000001000000

Water potential Ψ (Jkg-1)

EM

C (%

)

yellow birchsugar maple

-106 -105 -104 -103 -102 -101 -100

1

DesorptionDesorption curvescurves

0

20

40

60

80

100

120

1101001000100001000001000000

Water potential Ψ (Jkg-1)

EM

C (%

)

yellow birchsugar maplebeech

-106 -105 -104 -103 -102 -101 -100

1

ResultsResults

Yellow birch

© Almeida 2005

Beech

© Almeida 2005

Sugar maple

© Martin Caron 2002

Results Results -- Wood anatomyWood anatomy

0

20

40

60

80

100

120

1101001000100001000001000000

Water potential Ψ (Jkg-1)E

MC

(%)

Yellow birchBeech

-106 -105 -104 -103 -102 -101 -100

1

Equilibrium moisture contentEquilibrium moisture content--water potential water potential relationship at 25relationship at 25°°C.C.

Results Results -- Wood anatomyWood anatomy

r > 1.44 µm

Void volume proportion of the wood elements.Void volume proportion of the wood elements.

0

10

20

30

40

50

Vessel Fiber lumina Rayparenchyma

Axialparenchyma

Void

vol

ume

(%)

Yellow birchBeech

0

20

40

60

80

100

120

1101001000100001000001000000

Water potential Ψ (Jkg-1)

EM

C (%

)

yellow birchbeech

-106 -105 -104 -103 -102 -101 -100

1

1.44 1.44 µµmm

0.21 0.21 µµmm

Equilibrium moisture contentEquilibrium moisture content--water water potential relationship at 25potential relationship at 25°°C.C.

1.44 1.44 µµmm

Incremental intrusion obtained by mercury porosimetry.Incremental intrusion obtained by mercury porosimetry.

0

2

4

6

8

10

12

0.0001 0.001 0.01 0.1 1 10 100 1000

Pore radius (µm)

Incr

emen

tal i

ntru

sion

(%)

Yellow birch

10-4 10-3 10-2 10-1 100 101 102 103 0

2

4

6

8

10

12

0.0001 0.001 0.01 0.1 1 10 100 1000

Pore radius (µm)

Incr

emen

tal i

ntru

sion

(%)

Yellow birchBeech

10-4 10-3 10-2 10-1 100 101 102 103

1.44 µm0.21 µm

Results Results -- Mercury porosimetry Mercury porosimetry

<Vessel radius (beech)> = 20 µm (anatomy)= 18 µm (porosimetry)

Results Results -- EMC x wood shrinkageEMC x wood shrinkage

0

3

6

9

12

0 20 40 60 80 100 120

EMC (%)

Woo

d sh

rinka

ge (%

)

volumetrictangentialradial

Sugar maple

Wood shrinkage as a function of the EMC at 25Wood shrinkage as a function of the EMC at 25°°C (yellow birch and beech) C (yellow birch and beech) and at 20and at 20--2121°°C (sugar maple, C (sugar maple, HernándezHernández and and BizoBizoňň 1994).1994).

0

3

6

9

12

0 20 40 60 80 100 120

EMC (%)

Woo

d sh

rinka

ge (%

)

volumetrictangentialradial

Yellow birch

0

3

6

9

12

15

0 20 40 60 80 100 120

EMC (%)

Woo

d sh

rinka

ge (%

)

volumetrictangentialradial

Beech

EMC: shrinkage statistically EMC: shrinkage statistically significantsignificantDiff = (T and Diff = (T and R)R)FullFull SaturationSaturation –– (T and R)(T and R)EMCEMC

Paired tPaired t--test Diff >0 test Diff >0

Results Results -- EMC x wood shrinkageEMC x wood shrinkage

31.131.14343Sugar mapleSugar maple30.930.94040BeechBeech29.229.24141Yellow birchYellow birch

FSPFSP(%)(%)

EMC EMC (%)(%)

Wood Wood speciesspecies

Table 1. EMC below which shrinkage was statistically higher than zero1.

1 α = 0.01 ** (1% probability).

0.0

0.5

1.0

1.5

2.0

0 20 40 60 80 100 120

EMC (%)

Woo

d sh

rinka

ge (%

)

volumetrictangentialradial

Wood shrinkage as a function of the EMC at 25Wood shrinkage as a function of the EMC at 25°°C (yellow birch).C (yellow birch).

Results Results -- EMC x wood shrinkageEMC x wood shrinkage

Tangential compliance coefficient = 1/ET

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 20 40 60 80 100 120

EMC (%)

Tang

entia

l com

plia

nce

coef

ficie

nt (G

Pa-1

)

Yellow birch

Compliance coefficients sCompliance coefficients s3333 in tangential compression as a function of the EMC at 25in tangential compression as a function of the EMC at 25°°C C (yellow birch and beech) and at 20(yellow birch and beech) and at 20--2121°°C (sugar maple, C (sugar maple, HernHernáándezndez and and BizoňBizoň 1994).1994).

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 20 40 60 80 100 120

EMC (%)

Tang

entia

l com

plia

nce

coef

ficie

nt (G

Pa-1

)

Yellow birchBeech

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 20 40 60 80 100 120

EMC (%)

Tang

entia

l com

plia

nce

coef

ficie

nt (G

Pa-1

)

Yellow birchBeechSugar maple

Results Results

17%

10%

13%

EMC x mechanical propertiesEMC x mechanical properties

ConclusionsConclusions

Shape of the boundary Shape of the boundary desorptiondesorption curve curve in the region governed by the capillary in the region governed by the capillary forces is particular to each wood species.forces is particular to each wood species.

At equilibrium, the radial, tangential and At equilibrium, the radial, tangential and volumetric shrinkage begin abovevolumetric shrinkage begin above FSP.FSP.

ConclusionsConclusions

At equilibrium, the MC affects the At equilibrium, the MC affects the tangential compliance coefficient beyond tangential compliance coefficient beyond the FSP.the FSP.

In the In the desorptiondesorption phase, loss of bound phase, loss of bound water begins in presence of liquid water. water begins in presence of liquid water. The EMC at which this loss begins The EMC at which this loss begins depends on wood species.depends on wood species.

BibliographyBibliography

HernHernáándezndez, R.E. and M. , R.E. and M. BizoBizoňň. 1994. Changes in shrinkage and . 1994. Changes in shrinkage and tangential compression strength of sugar maple below and above tangential compression strength of sugar maple below and above the fiber saturation point. the fiber saturation point. Wood Fiber Wood Fiber SciSci.. 26(3):36026(3):360--369.369.

SiauSiau, J.F. 1995. , J.F. 1995. Wood: Influence of moisture on physical properties.Wood: Influence of moisture on physical properties.Virginia Polytechnic Institute and State University, VA.Virginia Polytechnic Institute and State University, VA.

Stevens, W.C. 1963. The transverse shrinkage of wood. Stevens, W.C. 1963. The transverse shrinkage of wood. Forest Prod. Forest Prod. J.J. 13(9):38613(9):386--389.389.

TiemannTiemann, H.D. 1906. Effect of moisture upon the strength and , H.D. 1906. Effect of moisture upon the strength and stiffness of wood. stiffness of wood. U.S.D.A Forest ServiceU.S.D.A Forest Service, Bulletin 70., Bulletin 70.

U.S. U.S. DepartementDepartement of Agriculture, Forest Service, Forest Products of Agriculture, Forest Service, Forest Products Laboratory. 1974. Laboratory. 1974. Wood handbook: Wood as an engineering Wood handbook: Wood as an engineering materialmaterial. USDA Agric. . USDA Agric. HandbHandb. 72. Rev. USDA, Washington, DC.. 72. Rev. USDA, Washington, DC.

Thanks!

Merci!

Table 2. Sorption tests characteristics.

--152 526 152 526 33 33 MgCl2 MgCl2 DesorptionDesorption--74 941 74 941 58 58 NaBrNaBrDesorptionDesorption--37 756 37 756 76 76 NaClNaClDesorptionDesorption--20 750 20 750 86 86 KClKClDesorptionDesorption--14 495 14 495 90 90 ZnSO4 ZnSO4 DesorptionDesorption

≈≈ 100 100 HH22OOAdsorptionAdsorptionEquilibration over saturated salt solutions at 25Equilibration over saturated salt solutions at 25°°CC

--5 0005 00096.431 96.431 --DesorptionDesorption--2 0002 00098.557 98.557 --DesorptionDesorption--70070099.492 99.492 --DesorptionDesorption--30030099.782 99.782 --DesorptionDesorption--10010099.927 99.927 --DesorptionDesorption

Equilibrium under a pressure membrane at 25Equilibrium under a pressure membrane at 25°°CC00100100HH22OOSaturationSaturation

Full saturation under distilled waterFull saturation under distilled water

Water Water potentialpotential(Jkg(Jkg−−11))

RHRH(%)(%)

Saturated Saturated salt solutionsalt solutionState of sorptionState of sorption

Methods Methods –– sorption testssorption tests

MethodsMethods

MercuryMercury porosimetryporosimetry

rP θγ cos2−=

γγ est la tension superficielleest la tension superficielle (0,485 N/m)(0,485 N/m)rr est le rayon du capillaireest le rayon du capillaireθθ est l’angle de contact avec le substrat est l’angle de contact avec le substrat

(de 90° à 180°, mercure = 130°)(de 90° à 180°, mercure = 130°)

State of

sorption

Chemical or

saturated salt

solution

Nominal

relative

humidity

(%)

Water

potential

(Jkg−1)

Radius of

curvature of the

air-water meniscus

(µm)

Full saturation under distilled water

Saturation H20 100 0 ∞

Equilibrium under a pressure membrane at 25°C

Desorption - 99.927 -100 1.440

Desorption - 99.782 -300 0.480

Desorption - 99.492 -700 0.206

Desorption - 98.557 -2 000 0.072

Desorption - 96.431 -5 000 0.029

ψθγ cos2−

=r -102 J/kg → rayon ≥ 1.44 µm

Vaisseaux (diam. ≥ 50 µm)

Table 3. Sorption tests characteristics.

Methods Methods –– sorption testssorption tests

Effect of the temperature in the beginning Effect of the temperature in the beginning of physical mechanical changes;of physical mechanical changes;

NMR of beech, sugar maple and tropical NMR of beech, sugar maple and tropical hardwood at different EMC hardwood at different EMC

(proportion of bound and free water x EMC)(proportion of bound and free water x EMC)

Works in progressWorks in progress