- September 01, 2006, David J. Bentley, Jr., Editor
Barrier Testing And Comparison In Pouch Packaging Structures
by Bill Minnich, AET Films
APPLICATION: Metallized OPP structures can provide better barrier properties than foil structures after folding.
Various methods have use to estimate the oxygen and moisture barrier of flexible pouch packaging. A series of experiments compared the practical barrier of pouches. Foil was the control compared with metallized oriented polypropylene. The intent of the experiments was to simulate flexing and handling that would normally occur through the conversion and distribution chain. Barrier data collected at various stages estimated and compared the potential degradation of initial barrier through practical usage. In one set of experiments, Gelbo flex testing simulated handling. In the second set of experiments, pouches filled with desiccant underwent a protocol of shipping and dropping with weight gain measurement over time.
In a ship and drop test, 24 pouches of laminations were made by hand and filled with the same amount of laboratory desiccant. Twelve pouches of each type were kept as controls. The other twelve were packed in a box and shipped from Delaware to California and back.
For OTR, a metallized OPP (MOPP) structure showed incremental loss of barrier as the number of flexes increased. A 0.000250 foil structure showed excellent barrier retention up to five flexes. At ten flexes the performance was equivalent to the MOPP. At 20 flexes, the lamination had fallen apart and no tests were possible. A 0.000285 foil structure retained its excellent barrier performance through ten flexes but also fell apart at 20 flexes making measurement impossible.
The conclusion from this study is that MOPP structures have lower barrier performance than foil structures when the lamination is in its original flat state. When folded, aluminum foil structures will often develop cracks and holes and may completely lose barrier characteristics in some cases.
Reducing Variability In Dart Measurement Associated With Dart Head Wear
by Mark Weber, Gil Arnould, and Jason Benoit, NOVA Chemicals Corp.
APPLICATION: A study to explore the effect of dart head wear and additive formulation on dart performance showed that dart head wear can lead to variation in results after testing 1000 samples.
Discrepancies in results from dart impact testing of films are a common occurrence. To evaluate potential explanations for these differences, a study explored the effect of dart head wear and additive formulation on dart performance. Results from this work indicated that dart head wear can lead to variation in results after testing 1000 samples. When evaluating dart impact behavior on a variety of films using new and conditioned dart heads, the degree of impact resistance and the formulation of the film both had a significant effect on results. Samples with relatively poor impact performance were less sensitive to dart wear as were samples formulated with antiblock and slip. The sensitivity of dart to additive formulation was a result of the coefficient of friction of the film. Samples with low coefficient of friction showed minimal dependence on the condition of the dart head. A program to address these concerns can ensure that excessive dart wear does not generate unacceptable discrepancies in dart performance.
Dart impact resistance testing is a commonly performed test that measures the toughness of a film when impacted by a falling dart. As specified in ASTM D1709-04, the reported dart impact value is the weight of the dart when 50% of film specimens fail under the prescribed test conditions. While the effect of variables such as film thickness, die lines, and film contaminants on dart impact resistance is common knowledge, large discrepancies in laboratory data often occur. Routine testing in our facilities indicated that certain films produced higher dart impact data when comparing phenolic dart heads used for many months with new, unused dart heads.
The study reported here examined dart head performance to develop a method to ensure that dart impact results were repeatable and reproducible.
To obtain the complete version of these papers, go to www.tappi.org, and select “the PLACE” under the Publications/Bookstore heading.