An Investigation of the Adhesive Interaction between Polyethylene and Silicone with DMA and AFM
Abstract: Stickiness between materials can be a challening task when dealing with the complex interactions and processes related to packaging engineering. Part of the problem is that many factors like temperature, pressure, surface treatment as well as surface roughness all could play a part in contributing to the stickiness between materials. In this thesis a literature study has been done to map out potential sources of adhesion between the silicone rollers and polyethylene on the inside of packaging material. This was followed up by a comparative characterization study with a mechanical test method, dynamic mechanical analysis (DMA) and different modes of atomic force microscope (AFM) of silicone, processed in different ways, and polyethylene. Due to the low adhesive properties as well as a not optimal peel method it was not possible to obtain quantitative values from the developed mechanical test method. However, by using the DMA it was possible to confirm that the silicone samples processed in different ways differed from each other in terms of storage modulus. It was also established that hydrogen peroxide has a softening effect on polyethylene, and therefore might act as an increasing stickiness factor. The AFM was used to aquire images that was later analyzed by different surface roughness parameters. The AFM was also used for force-distance spectroscopy where it was possible to distinguish how the pull-off force differed between the different silicones in mind. By comparing how two silicones, one with silicone oil and one without, behaved at increasing temperature it was possible to see how the silicone oil at room temperature increased the pull-off force required. The explanatory argument for this was hypothesised to be due to an increase in capillary effect for the silicone sample that contains oil. At elevated temperature however it seemed to be the case that the silicone without oil showed a trend of higher pull-off force in relation to temperature, but this relation was not apparent with the sample with oil. The high uncertainty in the AFM measurements require more experiments and data points to be obtained in order to draw any firm conclusions of the result.
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