Mettler Toledo's TMDTA840 uses thermal analysis to investigate the shrinking behaviour of polyethylene (PE) film in two different directions.
This yields valuable information about the direction of film movement.
Samples of porous polyethylene film were heated from 25C to breaking point at a heating rate of 5K/min in a nitrogen atmosphere with a load of 2mN.
The load used was slightly higher than the minimum force to ensure the films remained stretched during the application process.
Samples were taken in two different directions of the film (crosswise, TD and lengthwise, MD).
To verify the results, two samples were measured in each direction.
The sample started shrinking as soon as it was heated in the lengthwise direction.
At around 130C, the sample was so viscous that it could no longer withstand the force applied and therefore started flowing, which led to a fast expansion.
In the crosswise direction, the sample started to expand slightly up to about 90C, before starting to shrink.
Again, at about 130C, it started flowing due to the viscosity of the sample.
In both directions, the shrinkage occured in several different steps.
This was explained by the subsequent melting of different crystals present in the sample.
The difference in the shrinkage behaviour of the two directions indicated that the film had been drawn in a lengthwise direction.
Mettler Toledo's TMDTA840 allows simple, rapid and reliable characterisation of PE film shrinking behaviour.
The different shrinking/expansion velocities identify melting processes of differently sized and shaped crystals that might have formed during the production process.
This yields valuable information on the quality and suitability of the PE used for packaging bottles or cans into six packs.
The TMA is well suited to this task and is therefore an extremely valuable instrument for quality control in the beverage industry.
