Characterization of Cell Walls Treated with Ethylene ...
Transcript of Characterization of Cell Walls Treated with Ethylene ...
Characterization of Cell Walls Treated with Ethylene Glycol
using Nanoindentation
Joseph JakesUniversity of Wisconsin-Madison
Materials Science ProgramUSDA Forest Products Laboratory
Advisor at UW: Don StoneAdvisors at FPL: Chuck Frihart, Robert Moon, Jim
Beecher
Outline• Nanoindentation
– Accounting for edge effects– Broadband Nanoindentation Creep
(strain rate sensitivity)• Experiments
– PMMA edge effects– Characterization of tracheid walls before
and after ethylene glycol treatment• Tracheid wall ultrastructure and
Norimoto’s model• Conclusions/Future Work
Ideal Nanoindentation Experiment
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( )ceff hA
SE =⎟⎟⎠
⎞⎜⎜⎝
⎛ −+
−=
d
d
s
s
eff EEE
22 1111 ννβ
S1
( )chALH max=
Lmax
hc
hc
SLhhc
maxmax ε−=
Infinite half-spaceDepth, h
Load
, L
Real Nanoindentation Experiment
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Cm
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Cm not accounted for
( ) ( ) ( ) ( )cmtcpceff hACChAChA
SE−
=== 11
Infinite half-spaceDepth, h
Load
, L
Nanoindentation of Wood
Cellular Structure
Use methods we have established to account for additional displacements from cellular
structure and edge
Edge
Nanoindentation of HeterophaseInterphase (Substrate-Adhesive)
Will the same method work for a heterophase interface?
Adhesive, Es,adh Substrate, Es,sub
Es,sub > Es,adhBehave similar to
free edge
Nanoindentation of Substrate-Adhesive Interphase
Will the same method work for a heterophase interface?
Adhesive, Es,adh
Constraining effect from stiffer phaseEs,sub > Es,adh
Substrate, Es,sub
Nanoindentation of Substrate-Adhesive Interphase
Will the same method work for a heterophase interface?
Adhesive, Es,adh
Constraining effect from stiffer phaseEs,sub > Es,adh
Substrate, Es,sub
Nanoindentation of Substrate-Adhesive Interphase
Will the same method work for a heterophase interface?
Adhesive, Es,adh
Constraining effect from stiffer phaseEs,sub > Es,adh
Substrate, Es,sub
measALH max=
( )( )smtmeaseff CCCA
E+−
= 1
( ) ( )( )smtceff CCChA
E+−
= 1
( )chALH max=( )( )mtc
eff CChAE
−= 1
Corrected Nanoindentation Methods
Measure areasfrom AFM images
Stone, Yoder and Sproul (SYS) Correlation
( )eff
sm EHLCCLC ++= maxmax
Plot C√Lmax vs √Lmax
Assume a structural compliance (Cs) is present
measALH max=
Jakes et al. (2008) J. Mat. Res. 23(4) pp. 1113-1127
No dependence on area!
( )( )smtmeaseff CCCA
E+−
= 1
External Compliances in Real Nanoindentation Experiments
• Machine Compliance (Cm)– Property of nanoindenter
• Constant for every indent performed– Standard methods established to account for Cm
• Structural Compliance (Cs)– Property of specimen and location of indent
• Cellular structure• Edge effects
– Use methods of Jakes et al. to measure Cs• Jakes et al. (2008) J. Mater. Res. 23(4) pp. 1113.
( )smtP CCCC +−=
Strain Rate Sensitivity Analysis
• Investigate deformation mechanisms by determining hardness as a function of strain rate during hold segment– Use Stone and Yoder creep analysis
• Stone and Yoder (1994) J. Mater. Res. 9(10) pp. 2524
• Determine strain rate sensitivity parameter:
)ln()ln(
HdHdε
υ&
=Ηdt
AdH
)ln(=ε&
Preparing PMMA specimen
• Specimen cut from an extruded PMMA rod
Nanoindentation surface prepared with diamond knife in ultramicrotome
3 mm
Extruded Edge
Preparing PMMA specimen
• Specimen cut from an extruded PMMA rod
Nanoindentation surface prepared with diamond knife in ultramicrotome
Extruded Edge
3 mm
MicrotomedEdge
Preparing UnembeddedSpecimens for Nanoindentation
• Current literature embed wood specimens in epoxy– Diffusion of epoxy components may be altering tracheid wall
• Developed microtoming techniques– Custom built diamond knife holder for sled microtome– Rotary ultramicrotome with diamond knife
C
AC
B
A
5 µm
Clearance and cutting angle of
diamond knife were both set to
approximately 5º for sled microtome
(SEM courtesy of Jim Beecher, FPL.)
Microtome cut
10 mm
Latewood
Experimental Procedure
• Indentation performed with HysitronTriboindenter– PMMA– Lobllolly pine
• Untreated• Treated with ethylene glycol
– Soaked in ethylene glycol for 3 days
(hysitron.com)
Berkovich Tip
Experimental Procedure
• Multiload indents used
0 100 200 300 400X Axis
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dDepth
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xis
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Hold for drift
0.01 s load
Hold for creep
• Areas measured from AFM images
( )eff
sm EHLCCLC ++= maxmax
Results: Edge effect in PMMA
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Distance to Edge, d (μm)
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Mod
ulus
,Es
(GPa
)
Assume Cs = 0Account for Cs
Bulk Es = 5.3±0.2 GPa
2 µm
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Distance to Edge, d (μm)
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Mod
ulus
,Es
(GPa
)
Microtomed edgeExtruded edge
Results: Microtomed vs. Extruded
Bulk Es = 5.3 GPa
0 20 40 60 80
Distance to Edge, d (μm)
050
100150200250300350400
Har
dnes
s,H
(MPa
)
Microtomed edgeExtruded edge
Results: Microtomed vs. Extruded
Bulk H = 270 MPa
Results: Microtomed vs. Extruded
10-4 10-2 100 102
dε/dt (s-1)
103
log(
H)(
MPa
) Bulk indentsMicrotomed edgeMicrotomed 7.5 um from edgeExtruded edgeExtruded 11.1 um from edgeExtruded 5.7 um from edge
ƲH ≈ 0.108ƲH ≈ 0.117
ƲH ≈ 0.146
Results: Unmodified Wood
2 µm
21 1.2 mN indentsEs = 21 ± 3 GPaH = 380 ± 20 MPa
6 0.8 mN indentsEs = 6 ± 1 GPaH = 340 ± 20 MPa
2 µm
Results: Comparison Before and After Ethylene Glycol Treatment
UntreatedEthylene Glycol
Treated
2 µm
2 µm
Results: Comparison Before and After Ethylene Glycol Treatment
2 µm2 µm
UntreatedEthylene Glycol
Treated
Results: Ethylene Glycol Treated Wood
2 µm
18 0.4 mN indentsEs = 6 ± 4 GPaH = 80 ± 10 MPa
5 0.2 mN indentsEs = 2 ± 1 GPaH = 80 ± 40 MPa
2 µm
No residual indent! Used area based on contact depth for calculations
Results: Strain Rate Sensitivity of Wood
10-4 10-3 10-2 10-1 100 101 102
dε/dt (s-1)
102
103
Har
dnes
s(M
Pa)
Untreated Cell WallUntreated Middle LamellaEthylene Glycol Cell WallEthylene Glycol Middle Lamella
ƲH ≈ 0.12
ƲH ≈ 0.07
ƲH ≈ 0.07
ƲH ≈ 0.04Unt ML
Unt CW
EG ML
EG CW
10 µm
Microfibril
(~10 nm)
Discussion: Ultrastructure of S2 Layer
Hemicellulose (red)
Lignin
(blue)
Cellulose
(yellow)
Cellulose
Lignin
Hemicellulose
Discussion: Norimoto’s Model
Lignocellulosic chain Hydroxyl group (-OH)
Microfibril
(~10 nm)
Hemicellulose (red)
Lignin
(blue)
Cellulose
(yellow)
Discussion: Norimoto’s Model for Ethylene Glycol
Microfibril
(~10 nm)
Hemicellulose (red)
Lignin
(blue)
Cellulose
(yellow)
Results confirm ethylene glycol
plasticizes both cell wall and middle lamella
No stable bonds
Summary for Loblolly Pine
Es (GPa) H (MPa) ƲH
Untreated CW 21±3 380±20 0.04
Untreated ML 6±1 340±20 0.07
Ethylene Glycol CW 6±4 80±10 0.07
Ethylene Glycol ML 2±1 80±40 0.12
• Testing both cell walls and middle lamella offers insight to effects of modification on lignin-rich and hemicellulose domains
Conclusion
• Capable of accounting for edge effects in determining Es, H and ƲH
• Extruded edge on PMMA has an effect on properties
• Ethylene glycol plasticizes cell walls and middle lamella– Greater change in ƲH for middle lamella
Future Work
• Develop processing-structure-property relationships– Relate Hardness vs. Strain rate curves to thermodynamic model
• Calculate activation energy and activation volume for deformation events
– Nanoindentation is only one component of characterization• Chemical analyses also important (IR, RAMAN, 2-d NMR)• TEM
• Use single component chemical modifications – Choose chemical probes based on solubility parameters to
selectively modify lignin and hemicellulose sub domains– Create a one stable bond modification (acetylation)– Create IPN’s in sub domains