This a presentation based on hermetic bag liner research from Cristine Ignacio and Dirk Maier of Iowa State University. Ignacio and Maier are researching the factors that influence the effectiveness of hermetic bag liners in achieving and maintaining a low-oxygen environment and preserving grain. The implications of this work include developing standards for hermetic storage bags, understanding the engineering properties of commonly used hermetic bags, and developing a basis for how many times a hermetic bag could be reused before losing structural and hermetic integrity. This presentation was given at the 2nd All-Africa Post-Harvest Congress and Exhibition in Addis Ababa and is being distributed on the SlideShare account of the Consortium for Innovation in Post-Harvest Loss and Food Waste Reduction. Iowa State University is a member of the Consortium.

1. Characterizing Engineering
Properties of Commercial Hermetic
Storage Bag Liners
Ma. Cristine D. Ignacio (PhD Student)
and Dr. Dirk E. Maier
2nd All Africa Postharvest Congress and Exhibition
September 17-20, 2019
African Union Commission Headquarters, Addis Ababa, Ethiopia
Agricultural and Biosystems Engineering

2. Agricultural and Biosystems Engineering
Hermetic Storage Technology
• Can effectively control insect activity in stored grain
and thus preserve grain quality
• Biological activity due to insect respiration reduces
oxygen eventually leading to asphyxiation of insects
1) Rigid Structure
a sealable metal or plastic silo
2) Flexible structure
typically a woven polypropylene (PP)
or jute sack with inner hermetic
plastic film liner(s)

3. Hermetic Storage Bag
Agricultural and Biosystems Engineering
 It’s effective
 It’s cost-
effective
 It’s accessible

4. Agricultural and Biosystems Engineering
No existing standards to rate hermetic storage bags
Not all engineering properties for commonly used hermetic
storage bags are available
Basis for how many times a hermetic storage bag liner could
potentially be used without losing hermetic and structural
integrity
Problem Statement
What are the factors that influence the effectiveness of hermetic
liners in achieving and maintaining a low-oxygen environment
and preserving stored grain?

5. Agricultural and Biosystems Engineering
Objectives
 To quantify key engineering properties:
 tensile properties
 dart impact energy
 tear force
 barrier properties
- oxygen transmission rate (OTR)
- water-vapor transmission rate (WVTR)
 To recommend values for international standards
on gas tightness

6. Materials and Methods
Agricultural and Biosystems Engineering
 Six commercially available hermetic storage bag liners were
used ---- RANDOMLY ASSIGNED FROM 1 TO 6
 All tests were conducted according to official ASTM standards
in ISU’s Food Packaging Research Laboratory
 All samples were conditioned at 23 ± 2o C and 50 ± 10% relative
humidity for not less than 40 hours prior to test
 Preliminary results will be presented (single liner)
 Statistical Analyses were done to check significant differences
between types of hermetic storage bag liners

7. 7
Agricultural and Biosystems Engineering
Hermetic Bag
Liner
Material Dimension
(cm x cm)
Capacity
(kg)
Thickness
(mm)
AGROZBAG multilayer liner is a co-
extruded bag combining
HDPE, MLLDPE and low
permeability barrier layer
130 x 80 100 0.090
ELITE 2 HDPE layers 137 x 70 105 0.080
PICS 2 HDPE layers 137 x 70 100 0.080
STOREZO Ultra-high barrier specialty
laminated blend of
polymers and LDPE
130 x 75 75 0.080
SUPERGRAIN (zipper bag) High-strength
PE with barrier layer
110 x 72 69 0.080
ZEROFLY Multilayer recyclable PE
with gas barrier
130 x 80 100 0.080
Manufacturers’ Specifications of Hermetic Storage Bag Liners

8. Hermetic storage bag liners can be classified
into two different categories:
extruded multilayers of
different polymers with a
high oxygen barrier
component
(such as EVOH or Nylon))
CATEGORY 1
high/low density
poly ethylene
(HDPE/LDPE) film without
special oxygen barrier
layer
CATEGORY 2
Agricultural and Biosystems Engineering
EVOH - Ethylene vinyl alcohol

9. Tensile Properties
Agricultural and Biosystems Engineering
Method: ASTM D882-18
Equipment: Shimadzu Autograph AGS-J Tensile Tester
Test specimen: strips of uniform width and thickness
Properties measured: yield strength, tensile strength,
maximum strain and toughness
Significance:
fundamental test that demonstrates how a polymer
behaves when subjected to pulling forces
affect usability of hermetic bag liner due to
handling, stacking and transport practices

10. Impact Resistance
Agricultural and Biosystems Engineering
Method: ASTM D1709-16a
Equipment: Oakland Series 800 Dart Drop Impact Tester
Test Specimen: 1 layer of hermetic bag liner
Significance:
measure performance during handling,
stacking and transportation
to ensure gas-tightness during storage
period, the hermetic bag plastic liner
should not rupture or fail due to impact
forces or load

11. Tear Strength
Agricultural and Biosystems Engineering
Method: ASTM D1922-15
Equipment: Oakland Series ME Tear Tester: Elmendorf Type
Test specimen: Rectangle with a slit 20 mm deep at the
center of the edge Ʇ to the machine direction
Significance:
measure performance during handling,
stacking and transportation (resistance
to tearing)
Insects not only eat and contaminate
grains but also make holes in plastic
liners

12. Oxygen Transmission Rate (OTR)
Agricultural and Biosystems Engineering
Method: ATSM D3985-17
Equipment: MOCON OX-Tran Model 2/21
Test Specimen: free of defects
Significance:
 low oxygen environment inhibit growth
and development of insect pests, mold,
and aerobic yeast
 affected by material composition and
thickness of plastic liner

13. Water Vapor Transmission Rate (WVTR)
Agricultural and Biosystems Engineering
Method: ASTM F1249-13
Equipment: MOCON Permatran W Model 3/33
Significance:
 maintains safe constant moisture levels in
previously dried commodities regardless of
ambient exterior humidity
 affected by material composition and
thickness of plastic liner

14. Summary of Preliminary Results
Agricultural and Biosystems Engineering
Key properties Category I Category II
Thickness, microns 69 to 90 80 to 89
Dart Impact Failure
weight, grams
399 to 1372 160 to 328
Tearing Force, gram-force
(Machine Direction)
451 to >800 217 to 529

15. a. Substantial differences in materials properties
between two categories of hermetic bag liners
b. Substantial differences among hermetic bag
liner brands for tensile properties, dart impact
failure weight and tear force
• Category II narrower value ranges
c. No existing standard method to test double
liners of Category II bags
• Testing potential methods in our lab
Preliminary Findings and Observations
Agricultural and Biosystems Engineering

16. Expected Outcomes
Agricultural and Biosystems Engineering
Basis for identifying “real” from “fake”
hermetic storage bags
Standard approach to rate hermetic crop storage
bags:
1. Maximum allowable or recommended OTR
and WVTR values
• Ensure hermetic conditions can be achieved
2. Limits for tensile properties, tear strength and
failure strength of hermetic bag liners
• Ensure bag liners are sufficiently strong to
hold crop

17.  Provide information on how many times
a hermetic storage bag liner could
potentially be used without losing
hermetic and structural integrity
Expected Outcomes
Agricultural and Biosystems Engineering
Basis for the durability of the hermetic bag liners

18. Next Steps:
 Recommend values for ASABE international
engineering standard
 Develop and specify test methods for hermetic
bags consisting of double/multiple liners
 Evaluate storage bags as affected by filling,
stacking and handling practices
Agricultural and Biosystems Engineering

19. Acknowledgement
Food Packaging Research Laboratory
Polymer and Food Protection Consortium
Center for Industrial Research and Service
Iowa State University
Agricultural and Biosystems Engineering

20. Thank you!
Maraming Salamat!
Agricultural and Biosystems Engineering