Cross-Section Multilayer Polymer Film Analysis

There are many ubiquitous products that we take for granted without really appreciating the technology that goes into developing them. When I started at MVA Scientific Consultants in 2010, one of the first projects I worked on was a multilayer polymer film analysis. A packaging manufacturer was doing a material deformulation analysis (also known as reverse engineering) of a competitor’s packaging material.

Having never seen the inside of packaging material, I never knew that so much research and technology was behind it. For a multilayer packaging analysis, the typical information that interests manufacturers are the layer thickness measurement, polymer identification of each layer and metal composition.

Also, manufacturers are interested in identifying any defects and/or inclusions in the polymer. Foreign particles can get into the polymer during manufacturing and these will form inclusions in the final product, which can shorten shelf life.

Packets of Androgel

This is the multilayer packaging material that was analyzed.

smeared polymer

This SEM image shows the cross-section of the packaging material. It was simply prepared with a razor blade cut. You can see some of the polymer was smeared. It is a quick and dirty way to prep the sample for a preliminary examination.

printing on package

This is the same sample prepared by an argon ion mill. The instrument sputters argon ions to polish the surface of the packaging polymers and metal. It creates a finely polished surface which is ideal for cross-section examination. With this, you can easily see the different layers in this multilayer polymer film. You can obtain the layer thickness measurement and the elemental composition of each of the layers. The thick, bright layer is made of aluminum.

cross section

This shows a brightfield optical image of the cross-section of the multilayer polymer film. A calibrated scale was used to perform the layer thickness measurement. The lighter color layer is metallic. The three darker layers are polymers.

cross section showing void

On the left is a brightfield reflected light image and on the right is a darkfield reflected light image. Both are at 500X magnification. Different illumination techniques provide different types of contrast, which can aid in seeing product defect in the sample. In these images, you can clearly see there is a void or air bubble in between layers. Layer separation is more common when there are more air bubbles.

cross section layers-1-2-3

raman spectra

After analyzing the layer structures and measuring the layer thickness, the next step is to identify the polymer composition in the packaging material. I placed the sample in a confocal Raman microscope and analyzed the different layers with a 785 nm laser to produce some beautiful spectra. This instrument is awesome when the samples cooperate and don’t fluoresce. Out of the three polymer layers, two were polyesters and one was a polyethylene polymer. The two polyesters showed some spectral differences, meaning they also had a molecular variation. The inner layer is usually the thicker layer, and in this case it was a polyethylene polymer.

That is it for now!

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