Case study - Problem solving for gels in co-extruded films

Norner provides failure analysis to the packaging industry.

 Norner provides failure analysis to the packaging industry on a regular basis. Here is an example of problem solving for gels in co-extruded films.

The presence of gels is a classic challenge of film extrusion. Such imperfections in form of lumps in the films can be cause by many different factors.

Analysing a gel may involve the following analytical techniques:

1) Sample preparation by microtome cutting cross sections of the film and gel.

2) Microscopy analysis to determine in which layer the gel is located and visual investigation with different contrast techniques to understand its nature.

3) Melting the cut film under microscope to determine if the gel is melting.

4) SEM analysis with element screening to determine the composition of the gel, which allows proper identification of especially inorganic contaminations.

5) FTIR analysis under microscope of the gel to determine the chemical fingerprint and identification of the composition or if degraded.

6) Advanced polymer analysis of samples of gel by e.g. DSC or GPC is possible if the gel has a shape/size, which makes it possible to cut it out of the matrix.

The attached picture illustrates a case we analysed for a customer. Based on both good equipment and very capable personell we can identify the type and cause of the gels. 

The film is a three layer coextruded PE film

  • LDPE is used in the outer layers and LLDPE in the core layer.
  • The gel is located in the LLDPE core layer.
  • The gel is partly cross-linked.
  • It is probably caused by thermal degradation during the extrusion process or by material in dead-zones in the extruder.



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