PET bottles are now ubiquitous when it comes to products such as soft drinks and water thanks to the ease with which they can be recycled. However, it’s difficult to use PET to make returnable bottles for more sensitive food items, such as juice or milk, as heat sterilisation of the bottles can have an impact on their integrity. Instead, they are typically made from glass or less recyclable types of plastic.
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But now, beverage packaging and bottling-machine manufacturer Krones and plastic packaging company Alpla have combined to develop a returnable PET container that provides an optimal environment for sensitive extended-shelf-life products in the cold chain.
The partners paid particular attention to the container cleaning process. ‘PET is less heat-resistant than glass,’ explained developer Ines Bradshaw. ‘So we had to find a way to ensure both a high level of microbiological safety and a high number of use cycles while cleaning at lower temperatures.’
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Krones carried out an elaborate series of tests at its development plant for washing technology in Flensburg, analysing the interaction of different bottle designs and cleaning processes. ‘The tests provided us with a very clear picture of the respective thermal, chemical and mechanical factors,’ said Bradshaw. The results showed that with the right combination of parameters – especially lye concentration, temperature, additive and mechanical impact – the containers could be effectively cleaned at temperatures of around 60°C.
A direct comparison of returnable PET and returnable glass also showed that over the course of several cleaning cycles, the alkaline cleaning medium visibly roughened the surface of the glass bottle, whereas nothing comparable could be observed with the PET containers. ‘For the filling of sensitive beverages in particular, consistent container quality can be an advantage that should not be underestimated,’ said Bradshaw.
Microbiological tests are currently being conducted to definitively establish whether the technology is safe. ‘Microbiologically, PET bottles that had gone through 25 cycles could not be distinguished from new ones,’ said Bradshaw. These tests will eventually be followed by a technical field test.
