1. Failure Analysis: Large Format Bags
Toward a material neutral
specification for
heavy duty shipping sacks

2. Objectives
• Multi-wall paper bags Specification and
Test Methods
• Other Specifications and Test Methods
– Heavy duty plastic bags
– Other bags
• Suggest a Sustainable Formula for Success
– Engineering properties
– Performance-based Specifications
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3. Context
• Multi-wall paper bags
– Mature Industry
– Widespread applications
– Renewable/degradable resource
• Heavy duty plastic bags
– Polymer improvements frequent
– Cost driven down-gauging
• Other bags
• Textile bags-new materials
• Premium performance
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4. Marketplace
• Commodities
– Little product differentiation
– Much packaging conformity
• FMCGs
– Market differentiation
– Package formats support segments and trends
• Sustainability Trend
– Renewable
– Compostable
– Source reduced
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5. Marketplace
Commodity Segmented Market
Woven
Paper Plastic
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6. Segmented Marketplace: Pet Food
$0.64/lb
$1.37/lb
$0.69/lb
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7. Specification: Multi-wall paper bags
UU-S-48 Version F: 1973
• “Kraft Paper” • “Extensible heavy duty Kraft
Paper”
– Min No. Walls Strength – Min No. Walls
– Min (∑ basis weights) – Min (∑ basis weights)
– Min avg (of each wall) dry – Min avg (of each wall) dry
tensile strength tensile energy absorption
strength (CD)
– Min avg (of each wall) dry Tear – Min avg (of each wall) dry
tearing strength tearing strength (MD+CD)
– Min avg outerwall (wet – Min avg outerwall (wet
strength Kraft) wet tensile Wet strength Kraft) wet tensile
strength Strength strength (CD)
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8. End Drop Test-CD stress
Force = mass acceleration
Energy = Force x
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9. Flat Drop Test-MD stress
Force = mass acceleration
Energy = Force x
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10. Force: k x
Strength
Increasing Force
Break
(Stress)
Elongation
X
(strain)
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11. Energy: Force x
Steeper: more
energy faster Break
Increasing Force
(Stress)
X
(strain)
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12. Multiwall bags: springs in series
1 1 1 • #4x “Heavy duty shipping
Keq K1 K2 sack extensible kraft paper”
– = 3 Walls
– ∑ basis weights 180
– Avg dry tensile energy
absorption* ( 19 CD; 57
MD+TD)
– Min avg dry tearing strength
– Min avg outerwall wet
tensile strength (CD)
* Foot pounds
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13. Strength so far
• Bag’s product accelerates until it stops.
• That force elongates bag material until
“limit” is exceeded.
Greater mass: more force
Higher drop: more force
• If limit is tensile strength, then bag fails!
• If not, product remains contained
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14. Tear
•Measures the force
–perpendicular to the plane of the paper
–required to tear through a specified distance
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15. Notched Tear v. Other
•Notched tear
–Force applied to thickness of the paper ( z)
• Initiating tear
–At edge (all 3 dimensions)
–Puncture
• 2 stages
1. Force to bend/break paper’s x-y plane
2. Force to break thickness
• Rate /surface area dependent
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16. Tear so far
• More complex than strength
• How tear initiated is key
• Modeling requires understanding use
context and review of risks.
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17. Wet Strength
• Strength of paper does vary with moisture
content.
• Suggests other environmental factors may
influence strength of other materials.
– Temperature
– Chemicals
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18. Stress/Strain of Plastic Films
Machine Direction
Cross Direction
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19. Tensile Energy Absorption of OPP
Cross Direction
177%
Machine Direction
100%
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20. Textiles
• Variability in all dimensions
• Design for worst case results in general over
specification
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21. Textile Tear Testing
• Variability in all dimensions
– Breaking strands
– Breaking bonds between strands
– Re-orienting strands
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22. 5 mil hexene lldpe film v. minimum
5 mil film
Abuse Stiffness Strength
Resistance
MD 1% Secant (lb)
600%
Peak Puncture Force (lb) Tensile @ Yield MD (lb)
Dart Drop Method A (g) 100% Tensile @ Yield TD (lb)
Elmendorf Tear TD (g) -400% Ultimate Tensile MD (lb)
Elmendorf Tear MD (g) Puncture Break Energy…
Break Elongation TD (%) Ultimate Tensile TD (lb)
Break Elongation MD…
Normalized Minumum C6 LLDPE
After Fiscus, 2005

23. 5 mil hexene lldpe film v. minimum
• Commodity resin optimum
– Stiffness: marginally adequate
– Strength: slightly over specified
– Tear/abuse: mostly over specified
• Converter option for trade off
– Blend in another resin
• greater stiffness
• Maintain other properties
• Down gauge to reduce cost
– Coextrusion for structural effect (“I-beam”)

24. What Next?
• Strength:
– Empirical Values-We (paper/plastic/textile) know
what works
– Theoretical Values-Finite element analysis
• Tear & Environment:
– What we want to protect against

25. How?
• Industry committee leadership
• Compliance labs-compile empirical data base
• MSU: theoretical analysis of strength
dynamics.

26. Thank you!
Questions or Comments?
How can I help?
tdunn@flexpacknology.com
404-376-4866
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