Solving a Polymer Sealing Problem with XPS Analysis

A client of Anderson Materials Evaluation had a problem with a heat sealed polymer debonding. The client needed to understand where the debonding was occurring. X-ray photoelectron spectroscopy (XPS) provided the answer. The heat sealed polymer was formed by heat sealing two sheets of polymer together. Each individual polymer sheet supplied by our client’s vendor was made of a sheet of fluorinated ethylene-propylene (FEP) laminated to a sheet of Kapton HN. Heat sealing was performed so that the FEP sides were sealed together. After heat sealing it was possible to pull the heat sealed polymer apart by hand. XPS survey spectra were collected on the new surfaces formed by pulling the heat sealed polymer apart and the survey spectra are shown in Figure 1 and 2. The two surfaces were arbitrarily referred to as side A and side B.

Figure 1. XPS survey spectra measured on side A of the debonded heat sealed polymer.

Figure 2. XPS survey spectrum measured on side B of the heat sealed polymer.

Only carbon and fluorine were detected in the survey spectrum measured on side A. The presence of only carbon and fluorine on side A demonstrates that only FEP (structure shown in Figure 3) is present on side A. Carbon, fluorine, nitrogen, and oxygen were detected on side B. In addition the C 1s peak in Figure 2 is split – the stronger, high binding energy peak due to the FEP carbons and the weaker low binding energy peak due to the Kapton HN, with structure shown in Figure 4.

Figure 3. Chemical structure of FEP.

Figure 4. The chemical structure of Kapton HN.

In Figure 5, a simplified model of the heat sealed polymer is presented. Only failure at interface 1b or interface 2b or within the FEP less than 5 nm from those interfaces would produce the XPS survey spectrum measured on surfaces A and B. Failure at any other interface or in any other region shown in Figure 5 would produce a different set of spectra for the two surfaces. The heat seal produced by the client was not the source of the debonding. The debond occurred within their vendor’s product.

Figure 5. A diagram of the materials, interfaces and interaction zones found in the heat sealed structure. The diagram is not to scale.
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