Evaluation of the welding properties of the surface layer on extruded polyethylene

Background
In a food packaging system the robustness of the sealing process is crucial. At the high speeds used in modern filling machines there is less than one second time for a seal, that needs to be tight and strong enough to protect the packed product, to be formed. During this time the polymer melts and interdiffuse, and finally recrystallizes during the cooling phase. The speed of filling machines is continuously increasing, and at the same time the speed of the extrusion process used to produce the packaging material is also increasing, which might influence the nature of the polymer in the sealing layers in a package. Altogether this calls for a better understanding of how the properties of the sealing layer influence sealing.

Master thesis
During the highly dynamic extrusion process used to produce the packaging material, a surface skin layer with different properties is formed at the surface of the sealing layer. The work has the goal to evaluate the nature of this layer and to find out how sealing, i.e. the welding process (molecular interdiffusion) and the interfacial strength build up (as described by percolation), is influenced.
Correspondingly, the work will contain a literature study, design of experiments to characterize and test the sealing properties of the surface skin (and of the material without the surface skin). Dependent on the outcome, an outline of what impact this has on the assumptions made in the theoretical models used to simulate the sealing process will be a natural extension and finally the results should be documented in a final report.

The master thesis will be partly done at KTH, Stockholm but it might also include activities at TP Units in Lund or abroad.

Supervisors: Prof. Ulf Gedde, KTH ([email protected])
Tetra Pak: Ph.D. Torbjörn Andersson

Examensarbetet finns även upplagt på hemsidan för Inst. för Fiber- och Polymerteknologi, se länkken nedan