Measuring Thermal Transitions of Multilayer Polymer Films with Dynamic Mechanical Analysis (DMA)

This article outlines a technique to establish the thermo-mechanical behavior of multilayer films comprising of polyamide (PA) and ethylene vinyl alcohol (EVOH) utilizing dynamic mechanical analysis (DMA).

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A range of industries use multilayer polymer films. For example, polymer laminates are employed in food packaging not only to protect food, but also to prolong shelf life and preserve flavors and aroma.

Film blowing or coextrusion methods are normally used to manufacture multilayer films. The process of coextrusion integrates multiple layers of individual polymers into a single film so that they are enhanced by the varying mechanical and chemical advantages (1).

In food packaging films for example, one layer could function as a barrier to humidity or oxygen, while the outer layer could comprise of a polymer that is suitable for welding.

Layers can additionally be used to position nanofillers like nanotubes or nanoclays, recycled plastics, pigments, UV blockers or other polymers or additives that offer protective features.

2. Samples

A multilayer food packaging film containing PA and EVOH was analyzed. A food packaging organization provided the film to be investigated. A sharp glass transition is not exhibited by either polymer as they share a semi-crystalline structure. The multilayer film had a thickness of approximately 0.2 mm.

Pure polyamide 6.6 has a glass transition temperature (T_g) of around 50 °C, various types of EVOH display T_g values ranging from 50 to 75 °C (assessed by tanδ peak).

Multilayer polymer films are intricate systems where bonding agents are used to bond various polymer layers together. The material’s thermo-mechanical behavior is highly influenced by bonding agents. The system’s material properties are influenced by the interactions between the various components.

Measurements of the multilayer film itself are crucial in order to estimate the performance of a product constructed from a multilayer film at specific temperatures. In the characterization of the supplied multilayer film, tensile tests were first performed to establish the amount of pre-strain necessary for the measurement.

An amplitude sweep was then performed to identify an appropriate range of stress amplitude (within the material’s linear viscoelastic range). A temperature ramp test was performed in the final stage to establish the thermal transitions of the multilayer film, for example the glass transitions of each specific layer.

This article demonstrates that DMA measurements utilizing a UXF fixture is an effective technique to carry out such measurements.

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References and Further Reading

1. Analysis of multi-layer polymer films. Guillory, Paulette, Deschaines, Tim and Henson, Pat. 4, s.l. : Elsevier, 2009, Materials Today, Vol. 12, pp. 38-39.
2. Mezger, Thomas. Das Rheologie Handbuch. ISBN 978-3-86630-663-2.

This information has been sourced, reviewed and adapted from materials provided by Anton Paar GmbH.

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