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

EXPERIMENTAL DETAILS

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

EXPERIMENTAL RESULTS

Method variability

Applied load & thickness

Laminates

METHOD VARIABILITY

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…

APPLIED LOAD

& THICKNESS

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

LAMINATES

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

FlexPackCon 2013