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FLEXIBLE PACKAGING
DURABILITY STUDIES Dr. Henk Blom
Rollprint Packaging Products, Inc.
Addison, IL USA
456
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Package durability
• Relevant across multiple industries
• Medical device packaging
• Food packaging
• Commercial packaging
• Inadequate packaging results in:
• Sterility breaches
• Over-concentration of medical solutions
• Food spoilage
• Shortened shelf-life
Common package defects Flex fatigue pinhole
Abrasion pinhole
Abrasion pinhole
Cut
Cut/puncture
Puncture
Package durability testing
Limitations
Significant cost involved
Pass/fail testing requires large sample sizes to be statistically meaningful
Time consuming – time spent on trucks and ships
Not predictive
Gelbo is usually not a good predictor of actual package performance
Process is usually iterative – may require several cycles to identify best
candidate
A predictive model?
• Is it possible to derive an empirical relationship between routine flexible material tests and package durability performance?
PF = a·Ex + b·Iy + c·Tz + … ???
• Would an equation (or family of equations) like this… • Enable easier screening of material candidates?
• Focus design efforts?
• Lead to innovative flexible package material designs?
• Be less expensive?
• Be faster?
Literature examples
Zapp – 1955 (Esso Labs)
“Abrasion of Butyl Rubber”
Studied abrasion properties
of tires using Lambourn
Abrader
𝐴𝑏𝑟𝑎𝑠𝑖𝑜𝑛 𝑙𝑜𝑠𝑠 = 𝑑𝑦𝑛𝑎𝑚𝑖𝑐 𝑚𝑜𝑑𝑢𝑙𝑢𝑠 𝑥 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛
𝑡𝑒𝑛𝑠𝑖𝑙𝑒 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ
Verghese – 1992 (Texas A&M) “Correlation of Pinhole
Development Due to Flexing to Mechanical Properties of Plastic Films”
Evaluated pinhole formation in 18 commercial flexible films using custom pinhole device
# 𝑝𝑖𝑛ℎ𝑜𝑙𝑒𝑠 = 𝑓(𝑚𝑜𝑑𝑢𝑙𝑢𝑠, 𝑖𝑚𝑝𝑎𝑐𝑡 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ, 𝑖𝑚𝑝𝑎𝑐𝑡 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ2)
Tan et al – 2008 (Beijing University of Chemical Technology)
“Abrasion Resistance of Thermoplastic Polyurethane Materials Blended with Ethylene-Propylene-Diene Monomer Rubber”
Investigated abrasion resistance of TPU/EPDM blends by abrasion loss
𝑊 =𝑃
2𝐻𝑡𝑔+ 12.13𝑘
𝑃1.5𝐷𝜇2𝐻0.5
𝐾𝐼𝐶
Taber Abrasion Test
• Equipment • Taber® Model 5750 Linear Abraser
• Flexible Material Kit
• Stylus is dragged back and forth across a sample supported in a holder over a mandrel
• Test stops when electrical contact is made between stylus and mandrel • # cycles is recorded
Special thanks to
the folks at Taber
Instruments!!
Materials
Monolayer
Biaxially oriented nylon (BOPA)
Cast nylon (cPA)
mLLDPE – Blown, metallocene
Oriented PET (oPET)
6% EVA copolymer
Cast PP (cPP)
5% EVA / 95% LLD blend
HDPE - Blown
Laminates
0.48 mil oPET / adh / 2 mil 6% EVA
0.75 mil cPA / adh / 2 m il 6% EVA
0.60 mil BOPA / adh / 2 mil LDPE
Experimental details
Variables
• Applied load
• Film thickness
• MD / TD
• Skin / Sealant (laminates)
Output
• Cycles to failure
Constants
• Stroke length (1 in)
• Stroke speed (30 in/min)
• Pin – 1.5 mm Ø
Side note: New ASTM test
method under development
by F02 committee
Observations
• Some data sets have narrow distributions, others have rather wide
distributions
• Data for a given material/load combination can span 2-3 orders of
magnitude
• No apparent underlying cause for the observed differences
Material
Direction
Load (g)
1 mil cPA1 mil BOPA
TDMDTDMD
279206279206279206279206
4000
3000
2000
1000
0
Cy
cle
s t
o f
ailu
re (
#)
Overview
• Plot of cycles to
failure (#) for
oriented and cast
polyamide
• Tested at two
applied loads (206
and 279 g)
• MD and TD data
• N = 15
Material
Direction
Test date
5 mil mLLDPE3 mil HDPE
TDMDTDMD
20132011201320112013201120132011
1400
1200
1000
800
600
400
200
0
Cy
cle
s t
o f
ail
ure
(#
)
Observations
• From this subset of the available data, method appears to be relatively
repeatable over time
• Materials with wide distribution in 2011 still broad; narrow distributions still
narrow
Overview
• Abrasion data for
HDPE and LLDPE
films
• Testing done in
2011 and 2013
• 279 g applied load
• N = 15
Material
Direction
Test date
2.5 mil cPP1 mil BOPA
TDMDTDMD
201320122011201320122011201320122011201320122011
5000
4000
3000
2000
1000
0
Cy
cle
s t
o f
ail
ure
(#
)
Overview
• Abrasion results
for oriented nylon
and cast propylene
• Testing done in
2011, 2012, and
2013
• BOPA tested at
279 g; cPP tested
at 206 g
• N = 15
Observations
• Data appears to be relatively repeatable over time in some cases, but not
in others
• BOPA MD 2011-2012 – did we get better at our methods?
• cPP MD or TD 2011 vs. 2013 – or did we get worse?
Method variability
• Test data for flexible packaging somewhat variable
• Source of variability?
• Inherent in the material?
• Surface? COF? Thickness? ???
• Test method?
• Sample loading? Contamination?
• Environment?
• Temperature? Humidity?
• Is it still a useful test?
• I think the following data will indicate that it is…
Overview
• Test data for cast PP
films of varying
thickness
• Semi-log plot against
inverse applied load
• Both MD and TD are
plotted
• Lines provided as
aids to the eye
Observations
• TD generally higher than MD – likely an orientation effect
• Thicker films require more abrasion cycles to failure
• Inverse relationship with applied load – increased load results in fewer cycles to
failure
• Clearly not a linear relationship!
Overview
• Test data for oriented
PET at various
thicknesses.
• Semi-log plot against
inverse applied load
• MD and TD data
pooled
• N = 15 in most cases
Observations
• Similar relationships as on previous slide
• Relationship to 1/applied load “stronger” for PET compared to cPP
Overview
• Abrasion data for
various materials as
a function of
thickness
• Log-log plot
• cPA, 5% EVA, and
6% EVA tested at
206 g
• oPET tested at 529 g
• cPP tested at 279 g
• N = 15
Observations
• As seen earlier, increased thickness leads to increased abrasion resistance
• Different materials have different sensitivities to thickness
• Low-modulus materials appear to be less sensitive to thickness than materials with
a higher modulus
Overview
• Oriented PET at
various applied loads
• Thickness range of
0.48 to 2.0 mil
• N = 15 in most cases
(but not for data at
206 and 279 g)
• MD and TD data
combined
Observations
• Clear relationship of both applied load and thickness to abrasion resistance
• Remarkably “linear” behavior on a log-log plot
• Could there be some underlying relationship to fundamental material properties?
Abrasion coefficient
• Thus far we have cycles to failure (f) data for a number of
materials as a function of thickness (t) and applied load (l)
– with data spanning several orders of magnitude
• How do we use a data set like this in modelling efforts?
• Can we reduce this data set to an abrasion coefficient (A)
for a given material?
• Can we factor out thickness and applied load?
𝐴 =log 𝑓 𝑥 𝑙
𝑡
Abrasion coefficient – ranking
Material Abrasion
coefficient
oPET 39.3
oPA 21.2
cPA 14.4
cPP 7.6
6% EVA 4.1
5% EVA/LLD 3.1
1
10
100
1,000
10,000
0.6 milBOPA
2.0 milLDPE
BOPA /LDPE
LDPE /BOPA
0.48 miloPET
2 mil 6%EVA
oPET /6% EVA
6% EVA/ oPET
0.75 milcPA
2 mil 6%EVA/LD
cPA /EVA
EVA /cPA
Average 3 2 136 17 168 9 3105 2120 5 7 733 140
Cyc
les
to
fai
lure
(#)
Conclusions
• Test method requires additional development to better
understand source of variability
• Abrasion resistance of flexible packaging materials
strongly related to applied load and material thickness
• Abrasion coefficient for monolayer materials provides a
means to rank materials and begin modelling efforts
• Laminate behavior does not appear to be simply related
to monolayer material abrasion performance
Recommendations
• ASTM test method needs to be finalized
• ILS conducted, P&B (precision and bias) determined
• Additional work required to understand and reduce test
variability
• Surface effects
• Friction effects
• Others?
• Gather information on many more materials (especially
laminates)
• Model development; collaborate with mathematical
modelling experts
• Understand how this test relates to actual distribution
Acknowledgements
Mr. Jason Obrecht
Mr. Chris Girgis
Mr. Nick Rohlfes
Ms. Jocelyn Blom
Ms. Rachel Blom