UNDERSTANDING WHY ADHESION IN EXTRUSION COATING DECREASES
WITH DIMINISHING COATING THICKNESS, PART III: ANALYSIS OF PEEL TEST
Barry A. Morris
DuPont Packaging and Industrial Polymers
Wilmington, DE
ABSTRACT
It is well known that in the extrusion coating process, peel strength to aluminum foil and other nonporous substrates
decreases with decreasing coating thickness. The peel strength is found to be more sensitive to changes in thickness
as the adhesion between the coating and substrate improves. An analysis of the peel test shows that changes in the
critical dimension of the deformation region at the peel front may be responsible.
INTRODUCTION
Extrusion coating involves extruding a molten polymer through a flat die onto a fast moving substrate and
quenching with a cold roll. The performance of the resulting structure depends on a number of processing and
polymer related properties. Of particular importance is the adhesion between the coating and substrate. As the
coating thickness is reduced, the adhesive strength generally decreases. In part I of this study [1], we looked at
adhesion to porous substrates and found adhesion is related to the amount of polymer that penetrates into the pores
of the substrate. The processing parameters that most influence penetration were shown to be coating temperature
and cooling in the nip. In part II [2], we examined adhesion to nonporous substrates such as aluminum foil.
Cooling in the nip and stresses imposed during drawing were found to contribute to the reduction in peel strength
with coating thickness.
Our analysis failed to discern the mechanism behind an observation from an earlier study [3] which showed that the
sensitivity of an adhesive’s peel strength performance to changes in coating thickness increases as the bond strength
of that adhesive increases. The earlier work involved blending an adhesion-enhancing (AE) additive into LDPE. As
illustrated in Figure 1, the results of a statistically designed experiment (DOE) show that the modified LDPE has a
steeper slope than LDPE alone when the peel strength to foil is plotted vs coating thickness. We will return to this
DOE experiment in the present work. For simplicity, we will refer to it as the AE DOE.
In the present study, we will first show that these results are general; the peel strength of an acid copolymer, which
has strong bonds to foil, is even more sensitive to changes in thickness than LDPE or the modified LDPE. We will
turn to an analysis of the peel strength measurement for an explanation.
EXPERIMENT
We coated three resins of increasing acid functionality onto a foil laminate to confirm the earlier work showing that
the peel strength to foil of better performing adhesives is more sensitive to changes in coating thickness. The three
resins were LDPE, a blend of 20% AE modifier and 80% LDPE, and an ethylene acrylic acid (EAA) copolymer (9%
AA, 10 MI). The AE modifier and EAA copolymer were supplied by DuPont. The coating conditions were:
• Die: Cloeren edge bead reduction die
• Substrate: 13-µm OPET/19-µm tie/9-µm Al
• Coating thickness: 20-50 µm
• Coating temperature: 330°C for LDPE and AE-LDPE blend; 288°C for EAA
• Die gap: 0.51 mm
• Line speed: 122 m/min
• Air gap: 127 mm
• Chill Roll temperature: 10°C
• Nip pressure: 0.4 MPa
The peel strength between the coating and foil was measured in the machine direction. The results are plotted vs
coating thickness in Figure 2. As the strength of the adhesion increases from LDPE to AE+LDPE to EAA, the slope
of the curve increases: the stronger the bond of the coating polymer to the foil, the greater is the sensitivity of the
peel strength to changes in thickness.
ANALYSIS OF PEEL STRENGTH MEASUREMENT
The peel test involves separating the layers at the desired interface, placing the “arms” into a tensile tester, and
measuring the force required to pull the specimen apart. Peel strength is reported as the force divided by the width
of the sample. Peel strength is known to be influenced by a number of factors, including pull speed, pull angle,
temperature, thickness of the adhesive, thickness of the substrates, and the tensile and viscoelastic properties of the
adhesive and substrates[4]. We hypothesize that the mechanics of the peel strength test is a critical factor for lower
peel strength at thinner coating thickness.
We will follow the convention of Kinloch, Lau, and Williams [5] for the development of concepts key to this
discussion.
Energy Analysis
An energy balance shows that the peel strength can be decomposed into contributions from the energy to create new
surfaces (the fracture energy, Ga), the energy dissipated during tensile deformation of the peel arm (Ge), and the
energy dissipated during bending of the peel arm near the peel front (Gdb). Mathematically, this can be written as:
P Ga + Ge + Gdb
=
b 1 + ε a − cosθ
where
Eq 1
P = peel force
b = width of peel strip
θ = peel angle
εa = tensile strain in the peel arm
Ga = fracture energy
Ge = energy dissipated during elongation of the peel arm
Gdb = energy dissipated during bending of the peel arm.
Figure 3 shows a schematic of the peel test geometry. Each of the energy contributions to the peel strength is a
function of thickness of the peel arm, g.
Elongation of the Peel Arm
Ge is related to the thickness of the peel arm times the area under the stress strain curve:
εa
Ge = g ∫ σdε
Eq 2
0
Here σ is the stress. If εa is constant, Ge is directly proportional to the thickness. If εa is not constant (i.e., a function
of thickness), the effect of thickness becomes nonlinear.
Bending of the Peel Arm
Gdb arises from bending of the peel arm and can be significant if plastic yielding occurs. Gent and Hamed [6]
studied the plastic yielding of OPET film during bending. They note that peel strength often has been observed to
go through a maximum at intermediate values of thickness. Gent concluded that at low thickness, plastic yielding
occurs, but the total energy that is dissipated is small. As thickness is increased, more energy is dissipated: peel
strength increases with Gdb. Eventually, the peel arm gets too stiff and less yielding occurs, which leads to a
reduction in Gdb and peel strength. At high thickness, no yielding occurs and Gdb is small.
Gent also proposed that the adhesion strength at the interface can affect Gdb. Low adhesion is less likely to lead to
yielding of the substrate. High adhesion can lead to large amounts of energy dissipation within the substrate in the
highly deformed region near the detachment:
“Plastic deformation of the stripping member can thus lead to an increase in peel strength in two ways: i) directly,
by an additional force representing the work required to propagate the bend in an elastic-plastic strip as peeling
proceeds, and ii) indirectly, by causing a larger deformation in the elastomeric substrate under the higher peel forces
and bringing about greater energy losses in this layer as a result.”[6]
As we shall see, higher adhesion can also lead to a greater initial angle of peel, θo, which can lead to a greater Gdb.
Recently, Pascal [7] discussed the effect of thickness on bending angle and peel strength in extrusion coating.
Fracture Energy
The fracture energy, Ga, can be decomposed into the product of two factors:
Ga = Wb(1 + Φ(R, T))
Eq 3
where Wb = work of adhesion or bonding and
Φ(R, T) = local energy dissipation at the peel front.
Here Wb is the bond strength. It encompasses the thermodynamic and chemical adhesion that occurs at the interface.
This term is typically quite small compared to the value of Ga but can be important because of its multiplying effect.
In the AE – LDPE blend system, the addition of AE adds chemical functionality to the LDPE, which we postulate
increases Wb.
The second term in equation 3, Φ, is the local energy that is dissipated as the detachment front, generally referred to
as a crack, moves through. A zone of deformation is created in front of the crack, as illustrated in Figure 4. Because
this deformation is related to the viscoelastic nature of the polymer, Φ is a function of rate (R) and temperature (T).
Φ is also a function of thickness, up to a point. As illustrated in Figure 4, when the thickness of the adhesive is
small, the local zone of deformation extends across the entire thickness of the adhesive. Indeed, the size of the zone
is constrained by the thickness. Small increases in thickness result in larger zones of deformation. Hence, at low
thickness, Ga increases with thickness. Above a critical value of thickness, gc, the size of the zone of deformation is
small compared to the thickness (right side of Figure 4); further increases in thickness have no effect on Ga. This is
illustrated in Figure 5.
The critical value of thickness, gc, is related to the tensile properties of the peel arm as well as the fracture energy:*
gc =
1 Ga E
2π σ y2
Eq 4
where E = Young’s modulus
σy = yield stress.
The dependence of gc on Ga makes sense in lieu of Gent’s comments above. Higher values of Ga (through, for
example, an increase in Wb) imply that the zone of deformation is larger, which in turn should increase the value of
g c.
APPLICATION OF PEEL STRENGTH MODEL TO EXPERIMENTAL DATA
Our analysis of the mechanics of the peel test shows that thickness has a significant effect on the measured peel
force. Moreover, both Gdb and Ga are a function of the adhesive strength, which may lead to an explanation of the
behavior in Figures 1 and 2. To apply these concepts to the foil coating structures, we will utilize a model
developed by Kinloch, Lau, and Williams [5]. They developed analytical expressions for Ge, Gdb, and Ga that we
solved iteratively using a computer for conditions that simulate the AE DOE.
Inputs for the model include the imposed peel angle and the tensile properties of the peel arm (Young’s modulus,
plastic yield strain, and work hardening parameter). Since Kinloch, et al., studied LDPE-foil laminates, we used
their tensile data in our analysis. We assumed the addition of AE to LDPE does not significantly change its tensile
properties. Our measurements were in a “T-peel” configuration, a geometry that is not explicitly solved for by the
model. We used 90° as the imposed peel angle (θ) as an approximation.
*
The critical thickness of the peel arm is that thickness which equals the radius of the plastic zone at the crack tip, ry. From Kinloch and Young
[8], a stress analysis for plane stress gives ry = (KI/σy)2/2π, where KI is the stress intensity factor. KI is related to the fracture energy by Ga = KI2/E
for plane stress. Therefore, ry = GaE/(2πσy2).
Figure 6 shows the results of the model for LDPE. The peel strength values (converted to the units of energy per
area) as a function of thickness are taken from the AE DOE results (bottom curve in Figure 1). The results show Ge
is small, reflecting our experimental observation that the peel arms did not elongate beyond the yield point. Ga is
large but not very dependent on thickness. Gdb has the greatest dependence on thickness.
Figure 7 shows the results for the 20% AE, 80% LDPE blend (top curve from Figure 1). Again Ge is small and will
be ignored for the rest of this discussion. Here both Ga and Gdb increase substantially with thickness. This may
account for the steeper peel strength curve in Figure 1.
Contribution of Fracture Energy to Peel Strength Reduction
Comparing Figures 6 and 7, we see that Ga for the blend is a strong function of thickness, whereas Ga for LDPE is
not. Using equation 4, we estimate gc to be around 10-20 µm for LDPE and 50-80 µm for the AE blend. Since our
coating thickness was in the range of 20 to 50 µm, this suggests that the LDPE coatings are near the plateau region
of Figure 5, whereas the AE-blend coatings are still on the slope. This is illustrated in Figure 8. Increasing the
bonding of the polymer to the substrate by adding chemical functionality increases gc. Over the thickness range of
interest, this change in critical thickness helps explain the sensitivity of the peel strength to thickness. An estimate
of gc for the EAA coating in Figure 2 of around 80-120 µm further validates this.
Contribution of Bending Energy to Peel Strength Reduction
As noted earlier, Gdb increases with increasing thickness for both LDPE and the AE-LDPE blend (see Figures 6 and
7). The slope of the AE-blend curve, however, is considerably higher. Following the argument of Gent, it appears
the addition of AE to LDPE increases the energy dissipated during bending of the peel arms. This is achieved
through a greater anchoring effect. A comparison of the initial peel angles (θo – see Figure 3) supports this. As
shown in Figure 9, model calculations indicate that the peel angle remains constant for the AE blend coating as the
thickness is increased. For the LDPE, coating the initial peel angle decreases as thickness is increased. For a given
thickness, the peel arm of the AE-blend coating is pulled back at a higher angle than for LDPE, expending more
energy during the peel strength measurement.
CONCLUSIONS
The mechanics of the peel strength test help explain the low peel strength performance of thin coatings. The energy
dissipated during bending of the peel arm decreases with decreasing thickness. Moreover, both the fracture energy
and bending dissipation are strongly influenced by adhesion. Greater adhesion increases the initial peel angle,
resulting in greater bending energy, and the size of the deformation zone, leading to a steeper rise in fracture energy
with increasing thickness. This may account for the divergence in slopes in our experiments; the greater bond
strength provided by the chemical functionality in the AE blend and acid copolymer gives rise to a steeper climb in
peel strength with increasing thickness than for LDPE.
PRACTICAL IMPLICATIONS
This work shows that increasing bond strength between the polymer coating and substrate does not always result in
higher peel strength. The peel strength depends on many factors beyond the bond strength, including the local
energy dissipation (Φ) at the peel front, the local peel angle, and whether the polymer yields or elongates. These
factors depend on the stiffness, thickness, viscoelastic response, and yield stress of the polymer. The physical
properties, in turn, do not affect each component of the peel strength in the same way. For example, reducing
stiffness may reduce the energy for bending the peel arm, but it may increase the fracture energy. The situation
becomes even more complicated for extrusion laminations where the properties of the second substrate may come
into play.
Despite these complexities, our findings suggest some general strategies for increasing the peel strength at low
coating thickness. For LDPE, increasing the bond strength by increasing oxidation (increasing temperature or using
ozone treatment) or adding modifiers may help. But as we saw with the AE modifier work, this may be most
effective for thick coatings. Without changing the physical properties, the improved bond strength may not be
enough to significantly improve the peel strength of thin coatings. Acid copolymers have even stronger bond
strength to aluminum foil than modified polyethylene. They are less crystalline than LDPE and, hence, have lower
modulus and yield stress. Thus, their peel strength may be higher than LDPE at a given thickness (see Figure 2),
even though they may be more sensitive to changes in thickness. Further changes in physical properties can be
obtained by incorporating soft comonomers such as acrylates or acetates into the ethylene backbone. EMA, EVA,
or acid terpolymers (ethylene-acid-acrylate) are examples. Primers may be needed for some of these polymers to
achieve good bond strength to the substrate.
In general, the polar ethylene copolymers, such as acid copolymers and EMA, have the right combination of
stiffness, yield stress, and chemical functionality to improve peel strength over LDPE at low coating weights. One
word of caution is that increasing the peel strength does not necessarily imply improved performance in a specific
application.
KEY WORDS
Adhesion, peel strength, extrusion coating, foil, coating weight, fracture mechanics
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
B. A. Morris, “Understanding Why Adhesion In Extrusion Coating Decreases With Diminishing Coating
Thickness, Part I: Penetration of Porous Substrates,” 2005 TAPPI PLACE Conference, Las Vegas, NV..
B. A. Morris, “Understanding Why Adhesion In Extrusion Coating Decreases With Diminishing Coating
Thickness, Part II: Nonporous Substrates,” 2006 TAPPI PLACE Conference, Cincinnati, OH.
B. A. Morris and H. T. Thai, “Improving the Adhesion of LDPE to Aluminum Foil Through Blending,” Annual
Technical Conference – Society of Plastics Engineers, 62, 1101-1105 (2004).
S. Wu, Polymer Interface and Adhesion, Marcel Dekker, Inc., New York, 1982.
A. J. Kinloch, C. C. Lau, and J. G. Williams, “The Peeling of Flexible Laminates,” International Journal of
Fracture, 66, 45-70 (1994).
A. N. Gent and G. R. Hamed, “Peel Mechanics for An Elastic-Plastic Adherend,” J. Applied Polymer Sci, 21,
2817-2831 (1977).
J. Pascal, “Ultraversatile Adhesives to Broaden the Possibilities of Extrusion Lamination,” 2006 TAPPI PLACE
Conference, Cincinnati, OH.
A. J. Kinloch and R. J. Young, Fracture Behavior of Polymers, Elsevier Applied Science Publishers, London,
1985.
The advice contained herein is based upon tests and information believed to be reliable, but users should not rely upon it absolutely for specific applications since performance properties will vary with processing
conditions. It is given and accepted at user’s risk, and confirmation of its validity and suitability in particular cases should be obtained independently. The DuPont Company makes no guarantees of results and
assumes no obligation or liability in connection with its advice. This publication is not to be taken as a license to operate under, or recommendation to infringe, any patents
Figure 1: Results of DOE varying coating thickness, coating
temperature, time in the air gap (TIAG) and % AE modifier
in blend with LDPE. Here temperature and TIAG are kept
constant and peel strength as a function of thickness and %
AE are plotted based on a statistical model of the
experimental results. From Morris and Thai [3].
Figure 2: Results of Coating Trial
Peel Strength to Aluminum Foil
OPET/tie/9-um Al/Coating
122 m/min, 127 mm air gap, 75 ms TIAG,
330 C Melt Temp (288 C for EAA)
1400
Peel Strength, g/25mm
1200
Peel Strength to Al Foil
Temperature, C = 310
TIAG, msec = 80
600
500
400
LDPE
800
20% AE, 80% LDPE
EAA
600
400
300
200
200
100
0
ECHIP
Peel Strength, g/25mm
700
1000
0
20
25
30
35
40
10
45
20
30
40
50
60
Coating Thickness, microns
Thickness, µm
Low %AE = 0
Middle %AE = 10
High %AE = 20
Figure 3: Peel Strength Test Geometry
Figure 4: Illustration of the Relative Size of the
Deformation Zone
Peel Test
P
Viscoelastic Deformation Zone in Front of Crack Relative to
Thickness of Peel Arm
θ0
g
θ
Figure 5: Theoretical Effect of Thickness on Ga
Figure 6: Results of energy analysis for LDPE coatings.
Peel strength and thickness data taken from AE DOE
model (Figure 1) with 80 ms TIAG and 310°C coating
temperature. Peel Energy model parameters: E = 150
MPa, alpha = 0.087, ey = 6.2%, θ = 90°.
Effect of Thickness on Ga
Peel Energy for LDPE
350
gc
Adhesive Thickness
Energy per Area, J/m2
Ga
300
250
Ga
200
Ge
Gdb
150
Gtot
100
50
0
0
10
20
30
Thickness, microns
40
50
Figure 7: Results of energy analysis for 20% AE, 80%
LDPE coatings. Peel strength and thickness data taken
from AE DOE model (Figure 1) with 80 ms TIAG and 310
°C coating temperature. Peel Energy model parameters:
E = 150 MPa, alpha = 0.087, ey = 6.2%, θ = 90°.
Figure 8: Scenario where Ga for LDPE and AE-LDPE
blends diverge because of differing values of gc.
Effect of Thickness on Ga
AE + LDPE Blend
Ga
Peel Energy for (20% AE+ 80% LDPE) Blend
350
LDPE
Energy per Area, J/m2
300
250
Ge
200
Gdb
Ga
150
Gtot
100
50
0
0
10
20
30
40
50
Thickness, microns
Figure 9: Comparison of initial peel angle (θο) for LDPE
and AE-LDPE blend. Peel strength and thickness data
taken from AE DOE model (Figure 1) with 80 ms TIAG
and 310°C coating temperature. Peel Energy model
parameters: E = 150 MPa, alpha = 0.087, ey = 6.2%, θ =
90°.
θ o vs. Thickness
Initial Peel Angle,
degrees
35
30
25
20
15
LDPE
10
80% LDPE, 20% AE
5
0
0
10
20
30
Thickness, microns
40
50
0
20
40
60
Adhesive Thickness, um
80
2007 PLACE Conference
September 16-20
St Louis, MO
Understanding Why Adhesion in
Extrusion Coating Decreases with
Diminishing Coating Thickness
Part III: Analysis of Peel Test
Presented by:
Barry A. Morris
Sr. Technology Associate
DuPont Packaging and Industrial Polymers
Motivation for Work
Morris and Thai, TAPPI PLACE 2004
Peel Strength, g/25mm
Temperature, C = 310.0
TIAG, msec = 80.0
700
600
Rapid Increase with
Thickness
500
400
300
100
ECHIP
200
20
25
30
35
Thickness, um
Low %AE = 0.0
Middle %AE = 10.0
High %AE = 20.0
40
45
Slow Increase with
Thickness
Part I: Porous Substrates
• Well known that adhesion decreases with
coating thickness to paper
• Examined 3 mechanisms
– Time in air gap
– Cooling in air gap
– Cooling in nip
• Conclusions
– Adhesion is related to penetration
– Penetration is influenced by polymer rheology,
coating temperature and cooling in the nip
Part II: Non-Porous Substrates
• Relooked at adhesion to foil
• Examined 4 mechanisms
–
–
–
–
Time in the air gap
Cooling in the air gap
Cooling in the nip
Stress from drawing
• Last two have impact on adhesion but do not
explain the different slopes
Outline
• Introduction
• Experimental Results
• Analysis of Peel Test
– Fracture mechanics
– Modeling of results
– Insight
• Conclusions
• Practical Implications
Extrusion Coating/Lamination
Die
Air gap
Substrate
Nip
Roll
Line
Speed
Chill Roll
Not drawn to scale
Experiment
• Purpose: Coat 3 resins of increasing
acid functionality onto foil to validate
previous findings
• Resins:
– LDPE
– Blend of 20% AE modifier, 80% LDPE
– EAA (9%AA, 10 MI)
Process Conditions and Set-up
• Die: Cloeren edge bead
reduction die
• Substrate: 13-μm
OPET/19-μm tie/9-μm Al
• Coating thickness: 2050 μm
• Coating temperature:
330 °C for LDPE and AELDPE blend; 288 °C for EAA
•
•
•
•
Die gap: 0.51 mm
Line speed: 122 m/min
Air gap: 127 mm
Time in the air gap: 75
ms
• Chill Roll temperature:
10 °C
• Nip pressure: 0.4 MPa
Peel Strength to Aluminum Foil
OPET/tie/9-μ m Al/Coating
122 m/min, 127 mm air gap, 75 ms TIAG,
330 ºC Melt Temp (288 ºC for EAA)
Peel Strength, g/25mm
1400
1200
EAA
1000
800
600
20% AE, 80% LDPE
400
LDPE
200
0
0
10
20
30
40
Coating Thickness, microns
50
60
Analysis of Peel Strength Test
Peel Test
P
g
θ0
θ
Peel Strength
• Measure of force to pull the specimen apart
• Contributions from
– Energy to bend the peel arm, Gdb
– Energy to elongate the peel arm, Ge
– Energy to create new surfaces, Ga
P Ga + Ge + Gdb
=
b 1 + ε a − cosθ
Elongation of the Peel Arm
Stress
Elongation of Peel Arm
Ge = thickness x area
under curve
εa
Strain
εa
Ge = g ∫ σdε
0
Bending of Peel Arm
• Bending energy goes through a maximum with
increasing thickness.
• Increased bonding at interface increases bending
energy.
• Angles can be affected as well.
Bending Energy
No yielding
at high
thickness
Gdb
Yielding,
but low
thickness
Thickness
Fracture Energy
Ga is the energy required to create new surfaces.
Ga = Wb(1 + Φ(R, T))
Wb is affected by changes in chemical functionality.
Φ is a function of the viscoelastic properties of the
polymer
Effect of Thickness on Ga
Viscoelastic Deformation Zone in Front of Crack and
Thickness of Peel Arm
Ga
Effect of Thickness on Ga
gc =
gc
1 Ga E
2π σ y2
Adhesive Thickness
Fracture Mechanics
• Thickness affects each component of the Peel
Strength
• Stronger bond strength results in greater
deformation and peel energy
Analysis of Peel Strength
Using Model Developed by Kinloch,et al.*
LDPE
350
Energy per Area, J/m2
300
250
200
Gtot
150
100
Ga
Gdb
50
Ge
0
10
20
30
Thickness, microns
*Kinloch, Williams, and Lau, Int J Fracture, 66, 45-70 (1994)
40
50
Analysis of Peel Strength
Using Model Developed by Kinloch, et al.
350
(20% AE+ 80% LDPE) Blend
Energy per Area, J/m2
300
250
Gtot
200
Ga
150
100
Gdb
50
Ge
0
10
20
30
Thickness, microns
40
50
Analysis of Peel Strength
350
300
300
Energy per Area, J/m2
Energy per Area, J/m2
LDPE
350
250
200
Gtot
150
100
Ga
Gdb
50
(20% AE+ 80% LDPE) Blend
250
Gtot
200
Ga
150
100
Gdb
50
Ge
Ge
0
0
10
20
30
Thickness, microns
40
50
10
20
30
Thickness, microns
40
50
Bending Energy Comparison
Gdb vs. Thickness
140
Gdb, J/m2
120
80% LDPE, 20% AE
100
80
60
LDPE
40
20
0
10
20
30
Thickness, microns
40
50
Initial Peel Angle
θ o vs. Thickness
Initial Peel Angle, degrees
35
80% LDPE, 20% AE
30
25
LDPE
20
15
10
5
0
10
20
30
Thickness, microns
40
50
Fracture Energy Comparison
Ga vs. Thickness
180
160
20% AE, 80% LDPE
140
Ga, J/m2
120
100
80
60
LDPE
40
20
0
0
10
20
30
Thickness, microns
40
50
Scenario of Why Ga has Different Slopes
Effect of Thickness on Ga
Ga
gc for AE + LDPE Blend is 5080 μ m
gc for LDPE is 10-20 μ m
0
20
40
60
Adhesive Thickness, μ m
80
Conclusions
• New experimental results validate earlier results
– Slope ↑ with chemical functionality
• Analysis of peel strength explains slope
– Each component of PS is affected by thickness
– Greater bond strength increases the sensitivity to
thickness by
• Increasing the bending energy and initial peel angle
• Increasing the natural thickness of the zone of deformation at
the peel front
Practical Implications
• PS is a complex function of bond strength and
physical properties
– Physical properties interact differently with the
various contributions to PS
– Example: Reducing stiffness may decrease Gdb but
increase Ga
• Tactics
– Acid copolymers - enhanced chemical functionality
(bond strength) and reduced crystallinity (stiffness)
over LDPE
– Softer polymers such as EVA’s, EMA’s and acid
terpolymers may be good choice for some
applications.
Thank You
PRESENTED BY
Barry A. Morris
Sr. Technology Associate
DuPont Packaging and Industrial Polymers
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