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Paper 9.3, Allen, Cheng

A Model to Predict the Ability of a Flexible Package to Contain Materials.

Richard Allen and Tammy Cheng Session 5 Paper 1

Paper 9.3, Allen, Cheng

Containment Testing of Flexible Packaging

• Cumbersome and time consuming.
• One test for each material.
• Subjective.

Is there a better way?

Paper 9.3, Allen, Cheng

Definitions

• Material = The item “contained” in the

package.

• Containment = Ability of package to hold a

material for a specified time without failure.

• Sealant = The heat seal layer.
• Adhesive = Adhesive or Primer
• Substrate = Supporting film, in this case

aluminum.

Paper 9.3, Allen, Cheng

The Concept

• To be destructive, a material must first

pass through sealant layer (permeation) AND must degrade the bond of sealant to substrate.

The probability of package failure = Permeability X Adhesive bond disruption.

Paper 9.3, Allen, Cheng

Permeation of contained material through sealant.

Low High

Should be contained: Both adhesive and sealant unaffected. May be contained: Sealant may swell. May be contained for a time: Until the material diffuses through sealant and disrupts bond. Difficult to Contain: Both sealant and adhesive may be affected.

Bond disruption by contained material.

Low High

Paper 9.3, Allen, Cheng

Axis 1: Permeation of contained material through sealant.

Paper 9.3, Allen, Cheng

Permeation of Materials Through Polymers.

P = D x S P = Permeation D = Diffusivity ~ How fast the material passes through the sealant. S = Solubility ~ How much material the sealant will hold.

Paper 9.3, Allen, Cheng

Primary Factors that Affect the Permeation of a Material Through a Sealant.

• Sealant composition, crystallinity and

Tg.

• Material composition and molecular

weight.

• Temperature.

Paper 9.3, Allen, Cheng

Diffusion Affected by Molecular Weight and Temperature.

Time for 1/2 of Material in 25 micron LDPE to Migrate.

0.0001 0.001 0.01 0.1 1 10 100 1000 10000 100000 1000000 500 1000 1500 2000 2500 3000 3500

Molecular Weight of Material (daltons)

Time (hrs.)

20C (68F) 50C (122F) 10 Years 1 year

1 week

100 years

Paper 9.3, Allen, Cheng

Swelling of Sealants in Various Materials (%)

Contained Material LDPE EAA Ionomer PP copolymer Water

• 0.9
• 3.1

IPA 2.1 19.1 13.0 2.9 Vinegar 1.0 0.7 Tabasco 1.0 0.7 2.0 0.6 Mineral oil 8.4 5.0 8.3 3.8 Motor oil 10.5 6.5 10.9 3.0 Skin-So-Soft 15.3 14.7 21.0 9.5 Dioctyl sebecate 4.8 4.8 4.8 4.8

Paper 9.3, Allen, Cheng

Observations.

• Polarity mis-match is important:

– Polar water does not swell these relatively non-polar sealants – Slightly polar alcohol and vinegar swell non-polar PE or PP little, but swell slightly polar EAA and ionomer. – Non-polar oils swell all sealants but slightly polar EAA better than non-polar PE.

• Crystallinity is important:

– PP is the most crystalline sealant tested and swells the least in just about all materials.

Paper 9.3, Allen, Cheng

Conclusion About Permeation

• Low molecular weight liquids can be

difficult to contain because they diffuse the fast.

• Sealant selection can be important.

– Diffusion through PP is 44 X slower than PE. – A polarity mismatch between sealant and contained material may help.

Paper 9.3, Allen, Cheng

Axis 2: Bond Disruption by Contained Material.

Paper 9.3, Allen, Cheng

Factors that Disrupt Bonds of Adhesives.

• Chemical:

– Competition for adhesive bonding sites by contained material. – Chemical reaction with adhesive

• Physical:

– Solubility of material in adhesive.

Paper 9.3, Allen, Cheng

Bond Disruption by Competition for Bonding Sites

Polyethylene Aluminum Surface

+ HO2CCH3 C O O C O O EAA Primer CO2H HO2C CH3 C O O CH3 C O O

Paper 9.3, Allen, Cheng

Bond Disruption by Chemical Reaction with Adhesive

CO2-R-O2C + R’OH CO2R’ + H-O-R-O2C

Polyester polyurethane Alcohol Lower MW polyurethane

Paper 9.3, Allen, Cheng

Physical Bond Disruption by Plasticization of the Adhesive by the Contained Material.

Modulus or Strength Failure under stress.

% Material (solvent) in Adhesive Small amounts of solvent can significantly weaken bond

Paper 9.3, Allen, Cheng

Average Peel Force after Immersion

• f (Al/primer/PE) in Material for 4

days.

Primer A (g/25mm) Primer B (g/25mm) None Film tear at 835 Film tear at 629 Water 331 Film tear at 548 Water/Ethanol 1:1 62 404 Soybean oil Film tear t1106 Film tear at 593 White Vinegar 18 240 Skin-So-Soft Film tear at 739 650/353 Hot sauce 180 362

Paper 9.3, Allen, Cheng

Permeation of contained material through sealant.

Low High

Should be contained: May be contained: May be contained for a time: Difficult to Contain: Water Alcohol Dioctyl succinate Alcohol / Water

• mixture. Wipes.

Acidic: vinegar and hot sauce Oils with no aggressive additives (e.g.. Mineral oil, soybean oil) Oils with semi-aggressive additives (e.g.. Hand Lotions.) Oils with aggressive additives (e.g.. motor oil) Dry foods

Most Robust Adhesives Needed Here L e a s t P e r m e a b l e S e a l a n t s N e e d e d H e r e

Results For (Al/primer/PE)

Bond disruption by contained material.

Low High

Paper 9.3, Allen, Cheng

Conclusions

• The probability of package failure =

permeability X adhesive bond disruption.

• Proper selection of sealant or adhesive

can maximize the integrity of the package over time.