PO 2011 Nano-layer Effects in Blown Barrier Films (pt 2)-8-2
Transcript of PO 2011 Nano-layer Effects in Blown Barrier Films (pt 2)-8-2
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Nano-layer Effects in Blown Barrier Films (part 2)
Henry G. Schirmer, BBS Corporation, Spartanburg, SC
Tom Schell, Curwood, Inc., Oshkosh, WI
Dr. Mark Pucci, Soarus LLC, Arlington Heights, IL
Dr. Ananda M. Chatterjee, Chatterjee Consulting LLC, Missouri City, TX
Abstract
First heat DSC analysis of blown barrier films containing
EVOH in nano-layer form has shown a lower crystalline
melting point than on reheat indicating subtle changes in
the lamella thickness that are consistent with a lower fold
period. Stretch orienting these nano-layer barrier films
especially containing alternating layers of N6 with EVOH
processed extremely well between the Tg of N6 and
EVOH and 100 C - well below the melting points of both
materials. Since these films were so highly deformable at
these low temperatures there is the implication that they
are also easily thermoformed as well. Barrier property
measurements have been made defining all of these new
films.
Introduction
The newly invented Layer Sequence Repeater (LSR) has
produced coextruded blown films that have internal
structures containing nano-layer bundles within a matrix
of micro-layers. These new films are showing certain
property differences that can’t be obtained from standard
micro-layer coextruded blown films.
This is the third paper in a series given at PO 2009 and PO
2010 (ref. 12 & 13) about the observed effects that nano-
layers have on blown film properties. The first paper
showed that nano-layers consisting of brittle materials
such as EVOH and COC produced films that were less
brittle than the single layer controls. The second paper
showed that nano-layers of EVOH with COC produced
barrier films with no enhanced barrier properties either
wet or dry. In fact the barrier properties appeared to be a
magnitude poorer than expected. This paper continues that
work in order to try to explain these anomalies.
The negative barrier performance anomaly reported in the
second paper was contradicted by a more positive one
reported in the first paper. This showed that Gelbo flexed
nano-layer films containing EVOH actually increased in
barrier performance after this abusive test.
An obvious explanation for the loss of barrier was that
pinhole voids developed within the EVOH nano-layers.
However, pinhole defects did not fit the Gelbo flex test
results. Another thought was that air quenching EVOH
nano-layers might have produced a more amorphous like
crystal. If nano-layers of EVOH were truly quenched to a
less densely packed crystal structure, this could have
reduced the overall degree of tightly packed crystals to a
point where the barrier was poorer. This explanation
would be consistent with the Gelbo flex results where a
more tightly packed crystal pattern may have been formed
by the work input of severe flexing. No one initially
thought that a resin mix-up might be responsible for the
poorer barrier results as was discovered here. This paper
will address these issues by measuring the crystalline
behavior of both test and control films using a Differential
Scanning Calorimeter (DSC) and relating that to barrier
and orientation results.
PAST HISTORY
US Patent 4,064,296 issued in 1978 teaches that EVOH
can be biaxally oriented at 100C or below when it is 2
mils thick and quenched in ice water as part of a 20 mil
thick EVA encapsulated coextruded tubing. This clearly
was the first indication that the crystalline structure was
altered by a rapid quench.
Polymers in a highly packed crystalline state simply
cannot be stretch oriented. Either most of the crystal
structure must be melted or it must be quenched to a more
loosely packed or amorphous state. The low temperature
orientation at 100C ruled out partial melting because the
orientation temperature would have to have been around
185C to melt the crystal structure. Instead, quenching to a
lower ordered crystalline state seems to be the only way to
account for the low orientation temperature of the above
patent. Since the Tg of EVOH is about 60C then any
temperature above this point would be suitable for
orientation if crystalline structure did not impede
stretching.
A polymer need not be totally amorphous for stretching to
be accomplished. However, any residual crystallinity must
be deformable and consistent with a loosely packed crystal
structure. Perhaps an analogy is the comparison of snow to
ice. Snow can be deformed easily while ice cannot.
Discussion
1. Definition of terms:
The Modular Disk Die has produced films containing 25
and more micro-layers independently of the LSR. While it
is generally true that as the number of micro-layers
increases, the individual layer thickness decreases for a
given total film thickness, the thickness of each of the
structural micro-layers are generally all in the same order
of magnitude. This doesn’t preclude that some micro-
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layers may contain the same material to make what would
appear to be fewer and thicker micro-layers. The reason
for doing this might be to simply gain increased output or
to gain some other processing attribute.
The Layer Sequence Repeater (LSR) operates as an
independent unit within a Modular Disk Die and inserts
nano-layer bundles within the matrix of micro-layers.
These are truly an order of magnitude thinner than the
surrounding micro-layers. So this definition of nano-layers
will be used here to differentiate nano-layers from micro-
layers and the difference will become very apparent from
the microphotographs shown in this paper.
2. Proprietary Multi-layer Blown Film Equipment:
MODULAR DISK DIE: Picture 1 shows a 25 micro-
layer barrier film being made from a 2x scale 18” 25-cell
Modular Disk blown film production die. Picture 2 shows
the internal micro-layer structure. In this case the 25
micro-layers were combined to make a “pseudo”-7 layer
PE/adh./N6/EVOH/adh./PE barrier film that is the
standard barrier film structure for the industry and is an
example of creating thicker and fewer micro-layers for the
sake of increased output and lower melt temperature.
Picture 1 - 18” 25 micro-layer Modular Disk Die
functioning to make 25 micro-layer barrier films.
Of course, while this in itself is useful, it is the opposite
end of the micro-layer spectrum. Noteworthy to mention is
that the same material that was used in the above micro-
layers also could be incorporated into nano-layers to make
fewer visible nano-layers. In some cases nano-layers from
one material alone may alter the physical properties from
differential melt shear conditions within the LSR and the
resulting nano-layers having higher melt orientation. So it
should be clear that there are many variations that can be
performed by using so many layers whether they are micro
or nano-layers.
While the “7 layer” micro-layer barrier film shown in
Picture 2 was made from the above 2x scale up of the lab
die, the coextruded nano-layer containing films reported
here were made using only the 1x lab die version. We
have had no reason yet to scale up the yet to be patented
LSR. That may come sometime in the future when the
need may arise.
Picture 2 - Standard Barrier Film thickness front and back
of the bubble at 2.55 mil each
As said earlier, the Layer Sequence Repeater (LSR) is a
separate device inserted within the module of a Modular
Disk Die. These coextruded films show an entirely
different layer structure from the micro-layer films; yet the
appearance of the bubble remains as if they were absent
(See picture 4 containing 75 nano-layers). However, some
more subtle processing differences have been observed.
For example, greater bubble stability has been witnessed
in some cases.
LAYER SEQUENCE REPEATER (LSR): The Layer
Sequence Repeater (LSR) was designed to repeat layers of
different materials in any desired sequence. It
compliments the Modular Disk Die technology and fits
within a module as an integral part or it may be used also
as a separate module. This is a desirable feature when
making rapid changes from say 25 to 75 nano-layers
because the entire module need not be disassembled.
The LSR is also capable of running the same material in
adjacent nano-layers as described above for micro-layers.
So not only can the material sequence be varied but the
FRONT SIDE PE+adhesive Nylon/EVOH/Nylon PE + adhesive PE + adhesive Nylon/EVOH/Nylon PE + adhesive BACK SIDE
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layer thickness can also be varied on the same or different
materials. For example a sequence might be as follows:
C/B/B/B/C/C/B/C/BBBB/C etc.
A typical bundle of 75 nano-layers within a matrix of 8
micro-layers 4 on each side is shown in picture 3. Note
that each of the 3 micro-layers on both sides used the same
polyethylene to make what appears to be a single layer.
Here you see that nano-layers are truly a magnitude
thinner than micro-layers.
Picture 3 - 75 Nano-layers in a matrix of 8 Micro-layers
Sample 12-2 Total Thickness = 3.2 mil
Picture 4 shows that blowing a 75 nano + 8 micro-layer
film in the lab was very similar to blowing single layer
films in production. However, like any other coextruded
film there are a myriad of coextrusion problems that may
be encountered and there were some new ones we
encountered in this work either because of extrusion rate
or materials used. True to its very thin layer nature, nano-
layer melt instability is often seen as very small chevrons.
Because there were no problems scaling up a lab die 2x,
we believe that an LSR can be scaled up with similar
results expected. So we believe that the films made for this
study should be applicable to a production environment.
To sum it up, nano-layer thickness is defined not by actual
thickness but by relative thickness when compared to the
surrounding micro-layer matrix. Further, nano-layers and
micro-layers both can use the same materials but nano-
layers will usually appear as a bundle of thinner layers
within the thicker micro-layer matrix.
Picture 4 - Laboratory 4” Upward Blown Film Line
Used to make Sample 12-2
3. Experimental Procedure:
3a. TEST FILM STRUCTURES
In order to address the possible barrier anomalies and the
ideas of causes, more wet & dry O2 barrier tests as well as
DSC analysis were made on the nano-layer test films.
These included the following test film examples.
Extruder/layer relationship=
A / D / {C/B/C/…25 nano-layers…B/C/B/C} / D / A
Samples 11/33 & 11-39=
LDPE/adh/{EVOH/COC.... COC/EVOH}/adh/LDPE
25 nano-layers
COC was used above only because it was a completely
amorphous resin and presumably would not hide or alter
crystalline structure of the EVOH during DSC analysis. It
did have very poor adhesion to EVOH and in some new
test structures was replaced with N6.
Samples 11/41, 11/42 & 11/43=
LDPE/adh/{N6/EVOH..… EVOH/N6}/adh/LDPE
25 nano-layers
3b. CONTROL FILM STRUCTURES
The 7 micro-layer control film series 11-29 to 11-32 was
tested for both DSC and O2 permeability. The control film
had a similar structural to the test films pattern but only 2
layers of EVOH on both sides of a COC layer.
Extruder/layer relationship=
A / D /C / B / C / D / A
Samples 11/29 - 11/32 =
LDPE /adh/EVOH/COC/EVOH/adh/LDPE
3 micro-layers PE 1 layer Vistamaxx 75 nano-layers of PP/Vistamaxx 1 Layer Vistamaxx 3 micro-layers PE
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Along with O2 analysis, a study of the crystalline structure
through the use of a DSC was expected to show any
differences related to crystalline behavior. For example, a
DSC 1st heat and 2
nd reheat cycle should give an indication
of the initial melting behavior as well as the annealed
behavior. Any unstable crystalline effects due to possible
quenching should be revealed during the 1st heating cycle
and these could then be compared to the annealed sample
during the 2nd
reheating cycle.
3c. ORIENTATION EFFECTS: Dry quenching of
coextruded EVOH was the key to its orientation below
100C and this implied that changes in crystallinity also
took place. Therefore to avoid water contact and possible
influence on water sensitive EVOH DSC analysis of liquid
N2 quenched thin EVOH samples was also done so that
these could be compared to the DSC curves of the test
nano-layer films. A selected test film was oriented by
stretching longitudinally to determine low temperature
deformation and if stretching would affect the barrier.
3d. EVOH BARRIER THICKNESS: Two methods
were used to determine barrier layer thickness. The first
method was to make a thickness approximation from the
extruder output curves and the second was to determine
the thickness by optical means.
The relative layer thickness values calculated from
extruder output data below were based on the following
expected values: A extruder (1.25”) delivering 10 lbs/hr
PE @ 40 rpm; B&C extruders (0.75”) at 44.65 rpm
delivering @ 3 lbs/hr each of EVOH & COC respectively
and extruder D (0.75”) @ 30 rpm delivering 2 lbs/hr of
adhesive resin.
Both test and control film structures contained identical
micro-layers A & D. Only the C/B/C structural portion
was varied from the 3 micro-layer control films to the 25
nano-layer test films. As the layer thickness estimates
calculated from extruder output show, the total equivalent
EVOH thickness was about .167 mil / mil total thickness
whether this was the sum of 13 EVOH nano-layers or the
sum of 2 EVOH micro-layers. The only EVOH difference
between test and control were the individual layer
thicknesses and the number and not the total equivalent
amount.
TOTAL OUTPUT - LAYER RATIO’S (Basis= 10 mil film)
A= 10 lbs/hr = (10)10/18 = 5.556mil (2 layers)
D= 2 lbs/hr = (10)2/18 = 1.111mil (2 layers)
C= 3 lbs/hr = (10)3/18 = 1.667mil (2 to 13 layers)
B= 3 lbs/hr = (10)3/18 = 1.667mil (1-12 layers)
Lbs/hr=10+2+3+3=18lbs/hr TOTAL = 10.001mil
Calculated barrier/total thickness ratio for test films was
1.667/10 = 0.167mils/mil. Since there were 13 EVOH
nano- layers in the test films, each nano-layer was about
1.67/13 = 0.128mil (3251nm) in a 10 mil film or
0.0128mil (325nm) in a 1 mil film.
In similar fashion, the calculated EVOH thickness of each
micro-layer in the control film was in the order of 1.67/2 =
0.835mil (20,920nm) in a 10 mil film or 0.0835mil
(2,092nm) in a 1 mil film.
The calculated thickness estimates gave support to the
actual optical measurements that were previously made
(ref. 12). Actual optically measured total nano-layer
thickness for each of the EVOH materials used was
averaged and reported in last year’s paper at about
.211mils/mil total thickness. The actual measure could not
be done here because of the difficulty in seeing the
individual layers of COC and EVOH. Both appear to have
similar refractive index and delaminating was common in
trying to get cross-sectioned specimens. Therefore the
slightly larger 0.211 mils/mil barrier figure was again used
here for more accuracy.
Experimental Work
In order to make the best possible comparison between the
test and control films, only the module that defined the
film structure was exchanged. One module was
constructed with 7 cells to make the 7 layer control films.
The other module contained 4 micro-layer cells and a LSR
to make the 25 nano-layer + 4 micro-layer test structures.
Both modules were exactly the same size and used the
same die. The LSR only occupied the space of 3 normal
cells.
Picture 5 – 2” Test Line used to make both 7 micro-layer
and 25 nano + 4 Micro-layer test films
Downward Blown Film Test Line: The test line used to
manufacture all films used in this study is shown in picture
5. It blew film downward into a portable converging frame
winder. To the left of the die was an independently
variable speed 0.75-inch extruder D that delivered the 2
micro-layers of adhesive adjacent to both sides of the 25
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nano-layer test barrier structure or the 3 micro-layer
barrier structure of the control film. To the right was a
triplex extruder that delivered 2 melts from 2 - 0.75-inch
extruders B and C to the LSR. These 2 extruders were
commonly driven at a 20/60/20 ratio from a 1.25-inch
extruder that delivered low-density polyethylene to the
inside and outside of the bubble. The triplex extruder was
run at 40 rpm while the opposing .075-inch extruder D
was run at 30 rpm for the duration of each run to make
both control and test films.
Test Films 11-18 to 22 vs. Control Films 11-29 to 32
The sample 11-18-test film series that were made earlier
was still very clear and had been drawn thinner and
thinner until sample 11-22 at 0.7 mil was made at the
maximum winder speed. The quality and clarity of all of
the films was excellent but there was no adhesion of COC
to EVOH. Picture 6 shows the dual problems of
delaminating layers and difficulty in seeing layers that
were not delaminated. The materials used were as follows:
25 nano-layers
PE/adh/{L-171EVOH/COC8007/L-171EVOH}/adh/PE
Picture 6a - Sample 11-18 Optical Micro-photo (1.6 mil)
Picture 6a had less layer definition because of
backlighting very thin slivers of cross-sectioned film.
Pictures 6b had better definition because of surface
lighting.
The sample 11-29 7-micro-layer control film series now
extruded was also very clear and it too was drawn thinner
and thinner until the maximum take away speed was
attained with sample 11-32 at 0.7 mil. Again there was no
adhesion between COC and EVOH. Picture 7 shows a rare
cross section of sample 11-29 without delaminating layers.
Both the above sample series were then submitted for wet
and dry barrier testing in spite of the lack of adhesion. The
results supported the barrier tests from the 2010 paper
(Ref 13) but in more detail.
Picture 6 b Sample 11-18
Picture 7 Sample 11-29 (1.7 mil)
Table 1 below summarizes the equivalent thickness of the
barrier layers from both 25 nano-layer test and 7 micro-
layer control films that were selected for barrier tests. Of
course, these measurements have some margin of error
and that should be considered in reporting the results of
testing.
25 nano-layer section some delaminating
layers during cross sectioning
PE/ Admer
EVOH/COC/EVOH
PE/ Admer
Sample Equivalent Thickness
ID Total EVOH COC
11-18 & 11-29 1.6mil 0.338mil 0.338mil
11-19 & 11-30 1.2mil 0.253mil 0.253mil
11-20 & 11-31 1.0mil 0.211mil 0.211mil
11-22 & 11-32 0.7mil 0.148mil 0.148mil
Basis for Equivalent Thickness (optical as in ref. 14)
COC & EVOH = 0.211mils/mil total thickness
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Table 1 EVOH and COC equivalent thickness
The equivalent thickness of EVOH within each of the test
and control films was within the range used in most
industrial barrier films. So the barrier results obtained on
each of these films and shown in table 2 would represent
values that would be present in most packaging films
being used today.
Barrier Performance Tests - Samples 11-29-32 in table 2
below were the 7-micro-layer control films. Two 27mol %
EVOH (L-171) micro-layers were present within the
single micro-layer barrier matrix of (EVOH/COC/EVOH).
3-micro-layers
PE/adh/{L-171EVOH/COC/L-171EVOH}/adh/PE
Samples 11-18b-22b were the 25 nano-layer test films
with a similar structure but having much thinner repeat
units of EVOH and COC. These samples contained 13
nano-layers of EVOH and 12 layers of COC at the same
total amount of material or equivalent EVOH thickness as
the above control films.
25 nano-layers
PE/adh/{EVOH/COC/EVOH}/adh/PE
However, the EVOH in 11-18b was most likely 44 mol%
ethylene not 27 mol% due to a resin mix-up. This was
discovered when DSC analysis was run on 11-18b and 11-
29. Graphs 1a & b show the difference in melting peaks
between the test film 11-18b and the control film 11-29.
The DSC data were obtained from 2 different laboratories
and the implication was clear that the EVOH identity in
sample 11-18b was in question. 44mol% ethylene EVOH
has a melting point of 164C and this is very close to that
melting point value observed by DSC for test film 11-18b.
The unfortunate resin mix up clearly was responsible for
the higher 02 permeation values we observed. This data
was preserved to show the difference in permeability
between test films containing 25 nano-layers of
EVOH/COC where the mol% ethylene is higher.
Test Films 11-33c, 39b, 41c, 42b, & 43b
DSC ANALYSIS (1st & 2
nd Tm differences) – The
above DSC analysis identified the resin mix-up between
“44mol%” and 27mol% ethylene EVOH. The DSC
analysis was then continued further to identify any
differences in EVOH melting points between the
quenched and annealed states. Another run repeated the
above work using both Soarnol DT 2904, a 29mol %
ethylene EVOH and Eval L-171, a 27mol% ethylene
EVOH. These 2 grades are known to be equivalent in
barrier properties under all humidity conditions, and
therefore can be compared to one another. The film
structures were as follows and were used primarily for
DSC studies to identify ∆Tm values.
Sample 11/33 = 27mol% ethylene EVOH/ COC
(1.5mil)LDPE 5563/Admer498/{EVOH/ COC..25 nano..
COC/ EVOH}/Admer498/ LDPE 5563
Sample 11/39 = 29 mol % ethylene EVOH/ COC (1.5mil)
LDPE 5563/Admer498/{EVOH DT2904/ COC8007..25
nano.. COC 8007/EVOH DT2904}/Ad. 498/LDPE 5563
Surprisingly the DSC results on the above films showed a
significant difference between the 1st heat Tm and the 2
nd
heat Tm. This is shown in the example below (graph 2)
and is typically indicative of changes in the lamella
thickness that are consistent with a lower fold period.
Graph 1a
Sample 11-18b
2nd
MP = 161C
Graph 1b
Sample 11-29
2nd
MP = 185C
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Graph 2 DSC 1
st and 2
nd heat curves for 11-33C
Both of the above samples gave similar ∆Tm results from
two Soarus Labs: one in the USA and the other in Japan.
These are summarized in table 2.
Table 2 ∆Tm of 29mol% & 27mol% EVOH in nano-
layers
DSC analysis was repeated on pressed samples of the
29mol% EVOH resin that were quenched in liquid N2 or
air-cooled. These results are shown in table 3.
Table 3 ∆Tm of N2 quenched vs. Air for 29mol% EVOH
Clearly there was the same quench effect with the pressed
samples of EVOH but to a lesser degree (∆Tm = 1.2C).
The N2 quench while very rapid on the sample surface
was probably slowed down in the interior of these thicker
(11-12mil) specimens due to the poor thermal conductivity
of EVOH.
The “quenched” lower melting point indicated that the
crystals were smaller in thickness (lower lamella fold
period) and the surface energy became more and more a
factor. Thermodynamics are such that since the crystal
had more "energy" associated with it, it would undergo the
transition to the liquid state at a lower temperature.
The Japan laboratory also concurred that the ∆Tm could
explain a difference in deformability. They felt that an
amorphous chain in a polymer crystal having a lower
melting point could deform the crystal more easily
because the connection between them would be reduced in
strength slightly due to smaller crystal size.
Following the above DSC tests another replacement 11-
18b series was run as 11-45D through 11-48 and again
tested for wet and dry barrier. This time the EVOH was L-
171 from an unopened labeled bag. Identification of the
new nano-layer series is as follows:
PE/adh/{EVOH/COC..25nano..COC/EVOH}/adh/PE
11/45A-D (nominal 1.6 mil) = 5563/A498/{ L-171/8007…25nano…8007/L-171}/A498/5563 11/46 (nominal 1.2 mil) = 5563/A498/{ L-171/8007…25nano…8007/L-171}/A498/5563 11/47 (nominal 1.0 mil) = 5563/A498/{ L-171/8007…25nano…8007/L-171}/A498/5563 11/48 (nominal 0.7 mil) = 5563/A498/{ L-171/8007…25nano…8007/L-171}/A498/5563
Because of the poor adhesion to EVOH, again COC was
used in the nano-layer structures above only because of its
amorphous nature and transparency in DSC work.
Substituting N6 was the practical end use goal as was
done with the preceding samples.
NYLON 6 / EVOH STRUCTURES
Replacing nylon 6 for COC resulted in the following
samples that progressed from thinner to thicker films as
indicated below:
Sample 11/41, 42, & 43b = 29mol% ethylene EVOH/ N6
LDPE 5563/PX3227/ {N6 3411/ EVOH DT2904/..25
nano../ EVOH DT2904/ N6 3411}/ PX3227/ LDPE 5563
(STRETCHED & UNSTRETCHED)
The preceding N6/EVOH structures were found to
coextrude very well and certainly were equal to the
COC/DT2904 film quality. Since N6 adhered very well to
EVOH, this was an ideal combination to continue this
study further into orientation work on the above thicker
sample 11/43b. The coextrusion quality was excellent and
a micro-photo of it is shown in picture 8 that follows.
ORIENTATION STUDY
As mentioned above, the ultimate aim in doing this work
was to obtain a more functional film that used N6 instead
of COC. N6 would adhere to EVOH and help impart more
toughness as well. Sample films, 11-41c and 11-42b, were
made thinner for barrier comparison purposes. The
thickest, 11-43b, was then oriented 2:1 and 3:1
longitudinally at between 160 –200F. The orientation was
very stable as if the film were rapidly quenched in cold
Sample 11-33C
1st MP=185.20C
2nd
MP=187.20C
∆Tm = 2.00C
Quench 1st heat 2
nd heat ∆Tm Thickness
N2 185.7C 186.9C 1.2C 11-12mil
Air 186.0C 186.9C 0.9C 11-12mil
Sample 1st heat 2
nd heat ∆Tm Lab
11-39b 181.4C 184.7C 3.3C USA
11-39b 183.5C 185.7C 2,2C Japan
(Average)…………………… (2.8C)
11-33c 185.2C 187.2C 2.0C USA
11-33c 181.7C 186.5C 4.8C Japan
(Average)……………………. (3.4C)
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water rather than air-cooled. Since sample 11-43b had a
new crystalline form of EVOH as indicated by the above
DSC work, that crystalline form must have been easily
deformable in order to stretch orient below 100C.
Picture 8 Sample 11- 43A (25 nano-layers of N6/EVOH)
The tubular orientation is shown in picture 9. Samples 11-
43b1 and 11-43b2 were oriented in this manner with
progressively higher stretch ratios. There was a distinct
tendency of the material to biaxially orient. But the
starting material at 2.5 mil was too thin to make a useful
film. Nano-layers of N6/EVOH certainly proved to assist
in orientation both biaxially and monaxially.
Picture 9 - Sample 11-43b being stretched 2:1@160-200F
POLYBUTENE-1 ANALOGY – Isotactic PB-1 resin
and its 2 crystal forms is another example of a quenched
form and an annealed or aged form of crystal. The
quenched form II also must be deformable because it
could also be oriented below 100C. The orientation work
for isotactic polybutene–1 is described in US patent
“Oriented Blends of Polypropylene and Polybutene-1”
(ref. 14).
When isotactic polybutene-1 is crystallized from the melt,
initially a soft metastable tetragonal crystal form II is
produced. Over storage time of about 1 week at 21oC the
form II crystals are transformed spontaneously and
irreversibly into the thermodynamically more stable
hexagonal form I (ref. 15).
The glass transition temperature (Tg) of polybutene-1 is -
21 degrees C so at room temperature the form II crystals
are not frozen in place like those in EVOH (Tg=60C) and
are therefore free to transform to the more stable state at
room temperature.
After stretching or under hydrostatic pressure the form II
crystals are transformed into form I in the solid state. The
transformation is also affected by temperature, molecular
weight of PB-1, tacticity, comonomers, additives,
impurities, sample thickness and gamma radiation (ref 15).
Form II has melting temperature about 115C; form I
(stable) at about 127C. So ∆Tm for these crystal form
differences is about 12C when compared to the lesser
∆Tm of 2-4 C for the nano-layer EVOH.
BARRIER TESTING
Samples 11-41c (1.8mil) and 11-42b (2.2mil) were made
thinner than 11-43b (2.5mil) and were also included in
table 4 for barrier measurement and comparison both wet
and dry. Please note that O2 transmission is shown using 2
common measures, one bases area on 100in2 and the other
(meter)2. Also note the equivalent EVOH is shown based
on .211mil/mil total thickness.
Please note that the more recently measured values for
permeability to O2 on nano-layer films showed no higher
values than on the micro-layer control films. Samples 11-
45 to 11-48 are in the same order of magnitude as the
control film samples 11-29 to 11-32.
While nano-layer film showed no difference in barrier
properties, the new and more deformable EVOH crystal
form within the nano-layers certainly contributed to the
usefulness of the film in its ability to be oriented. Because
of the ease in orienting these films at a temperature below
100C, we also must imply that thermoforming within these
parameters would also be an attribute of nano-layer films.
9
Table 4 - O2 Barrier Measurements (Lab 1 Data)
Sample
OTR @ CC/100 IN2 /CC/M2 (0% RH, 23C)
OTR @ CC/100IN2 CC/M2 (85% RH, 23C)
Mils total Mils EVOH
11--29 0.015/.233 0.158/2.45 1.8 / .38 11--30 0.023/.357 0.240/3.72 1.2 / .25 11--31 0.026/.403 0.256/3.97 1.0 / .21 11--32 0.042/.651 0.471/7.30 0.7 / .15 11--18b 0.471/7.30 0.881/13.66 1.4 / .30 11--19 0.491/7.61 0.930/14.42 1.2 / .25 11--20 0.630/9.77 1.152/23.56 1.0 / .21 11--22b 1.029/15.90 1.810/28.06 0.7 / .15 11—41c 0.0365/.5645 0.2670/4.14 1.99 / .42 11—42b 0.0240/.3715 0.2195/3.40 2.10 / .44 11--43b 0.0295/.4510 0.1040/1.61 2.33 / .49 11--43b1 0.0385/.6005 0.2695/4.18 1.56 / .33 11--43b2 0.0350/.5456 0.2880/4.47 1.24 / .26 11--33b 0.046/0.72 0.149/2.30 1.57 / .33 11--39 0.060/0.92 0.130/1.98 1.93 / .41 11—45d 0.043/0.66 0.320/4.93 1.67 / .35 11--46 0.058/0.90 0.070/1.05 1.06 / .22 11--47 0.072/1.11 0.360/5.47 1.08 / .23 11--48 0.116/1.80 0.560/8.75 0.73 / .15
The data contained in table 4 was then put into a single
graph in order to show the differences in barrier both in
the dry and wet states. Graph 3 is very clear in showing
that the 13 nano-layers of “44mol %” EVOH produced a
film that was a poorer barrier than the 2-micro-layers of
27mol% EVOH.
The encircled areas of graph 3 capture the wet and dry
barrier data. This data shows that the barrier of 25 nano-
layer films is in the same range as the 7 micro-layer
control and that the barrier does not change if nylon is part
of the structure or not. Further, both 27mol% and 29mol%
EVOH appeared to be very similar in barrier values.
Comparing all of the encircled values to the much steeper
slope of the 25 nano-layer “44mol %”EVOH test films,
samples 11-18 to 22 shows that the higher mol% films
deteriorate in barrier far more as the film thickness
decreases. The higher “44mol %” EVOH was clearly
responsible for the poorer barrier observed in the earlier
2010 paper (ref. 13).
Nano-layer N6/29mol % EVOH samples 11-41 through
43 whether blown or oriented also compared favorably
with the barrier values of the 7 micro-layer control film.
Please note specifically that because the 25-nano-layer
samples 11-41c, 42b and 43b, 43b1 & 43b2 used 29mol %
ethylene EVOH and were still in the same order of
magnitude as the 7 micro-layer control film. From this
data nano-layers did not appear to enhance barrier
properties of EVOH but at the same time neither did the
barrier diminish as was earlier reported in error due to the
resin mix up.
Some of the earlier anomalies reported may have been
partially due to orientation effects. Certainly we know now
that there are crystallinity differences that take place,
particularly with EVOH in nano-layer form as it is cooled.
These differences do not appear to increase or decrease
the overall barrier properties but certainly make it easier to
deform as in orientation and thermoforming.
Graph 3 - Barrier performance of 2 micro-
layer EVOH vs. 13 Nano-layer EVOH films
SUMMARY OF BARRIER TESTS
3 Micro-layers = 25 Nano-layers in barrier
27mol% = 29mol% EVOH in barrier
N6/EVOH = COC/EVOH in barrier
“44mol%” 25 nano-layers
27 & 29mol% EVOH wet
27 & 29mol%
EVOH dry
10
SUMMARY & CONCLUSIONS
1. Quenching 11-12mil thick samples of EVOH into
liquid N2 produced a lower melting point crystal
structure (∆Tm=1.2C) than air-cooled (∆Tm=0.9C) or
annealed EVOH as measured by DSC.
2. Nano-layers of EVOH in blown film produced an even
lower melting point crystal structure (∆Tm=2-4.8C)
than the N2 quenched samples probably because the
significantly higher surface area and lower mass may
have actually cooled the material faster internally.
3. The lower melting point crystal structure is consistent
with a lower density thinner crystal showing changes in
the lamella thickness having a lower fold period. The
lower density crystal may also have an amorphous
chain going through it aiding in the ability to deform.
4. The nano-layer EVOH/N6 films were oriented
longitudinally at 2 & 3:1 stretch ratios at a temperature
between Tg and 100C, well below the melting point of
both materials. This confirmed the ability of the lower
melting EVOH crystals to deform. Similar crystal
deformation also seems to be present in the N6 as well.
5. The oriented films kept their barrier properties
compared to the micro-layer controls even though they
were thinner as a result of stretching.
6. EVOH in nano-layer form had barrier properties
similar to EVOH in micro-layer form. However, the
new lower density thinner crystalline form being more
deformable aids in orientation around Tg and by
implication easier thermoforming as well.
ACKNOWLEDGEMENTS:
1. Ken Toyosu at the Soarus Lab for his help with
DSC studies.
2. The people at Nippon Gohsei in the Japan Lab
for their corroboration of DSC analysis.
3. The people at the Curwood lab for their initial
DSC work and extensive barrier testing.
REFERENCES
1. Comparison of Irreversible Deformation &
Yielding in Micro-layers of PC with PMMA
& Poly (styrene-co-acrylonitrile) Kerns,
Hsieh, Hiltner, Baer - J. of Applied Science
Vol.77, 1545-1557 (2000)
2. The Modular Disk Coextrusion Die –
Schirmer Polyolefins 2000
3. New Compositions of Matter from The
Modular Disk Coextrusion Die - Schirmer,
Love, Schelling, Loschialpo - ANTEC 2000
4. Breathable Polymer Films Produced by the
Micro-layer Coextrusion Process Mueller,
Topolkaraev, Soerens, Hiltner, Baer - J.
Applied Science Vol. 78, 816-828 (2000)
5. Micro-layer Coextrusion Technology Baer,
Jarus, Hiltner - ANTEC 1999
6. Modular Disk Coextrusion: Production Rate
Tests with the 9” flex-Lip Die Schirmer -
Future-Pak 1999
7. Oxygen Barrier Enhancement of PET
Through Physical Modification Sekelik,
Nazarenko, Stepanov, Hiltner, Baer -
ANTEC 1998
8. Novel Structures by Layer Multiplier
Coextrusion - Nazarenko, Snyder, Ebeling,
Schuman, Hiltner, Baer - ANTEC 1996
9. 25 Micro-layer Blown Film Coextrusion Die
– Schirmer - Polyolefins 2008
10. Exploratory Experiments on Solid-State
Foaming of PLA films and COC/LDPE
Multi-layered Films - Lu, Kumar, Schirmer -
ANTEC 2009
11. Improved Flexible Packaging Film
Performance via Layer Multiplication- Sam
Iuliano – Polyolefins 2009
12. Nano-layers in Blown film – Schirmer,
Jester, Medlock – Polyolefins 2009
13. Nano-layers in Blown Barrier Films –
Schirmer, Jester, Medlock, Schell – PO 2010
14. Oriented Blends of Polybutene –1 and
Polypropylene –Schirmer–US Pat. 3,808,304
15. A.M. Chatterjee, “Butene Polymers”,
Encyclopedia of Polymer Science and
Engineering, Vol 2, 2nd
. Ed, 590 (1985)
11
AUTHOR CONTACTS
Henry G. Schirmer
BBS Corporation
2066 Pecan Drive
Spartanburg, SC 29307
Tel: (864) 579-3058
E-Mail: [email protected]
Tom Schell
Curwood, Inc.
2200 Badger Avenue
Oshkosh, WI 54904
E-Mail: [email protected]
Dr. Mark Pucci
Soarus LLC
3930 Ventura Drive, Suite 440
Arlington Heights, IL 60004
E-Mail: [email protected]
Dr. Ananda M. Chatterjee
Chatterjee Consulting, LLC
Missouri City, TX 77459
E-Mail: [email protected]