Krones and Alpla develop returnable PET bottles

Returnable PET containers, like those usually used in the bottling of soft drinks or water, are easily recyclable but it is difficult to use them in more sensitive food items, such as juice or milk in the cold chain, as sterilising the bottles with heat can impact their integrity. Now, Krones and Alpla, beverage and packing companies respectively, are cooperating to develop a returnable PET bottle that can be used for these kinds of extended shelf life products that would otherwise be packaged in glass or less recyclable plastic. These products have different requirements and regulations than those of soft drinks or water and therefore recyclable PET products need to be specially designed to hold them. After some initial testing that produced promising results, Krones and Alpla committed to developing a usable product that fulfilled these unique requirements.

The choice of which packaging to utilise for a product is defined by various parameters, from regulations and requirements to sustainability, and yet returnable PET often won’t enter into the equation at all. “Which type of packaging performs best from an ecological perspective depends on a number of factors and must be evaluated individually for each use case. And yet they can offer outstanding environmental performance, especially if they are distributed mainly regionally,” said Martina Birk, who is responsible for the enviro sustainability program at Krones.

“Until now, the main applications for returnable PET containers have been carbonated soft drinks and water,” said Jörg Schwärzler, returnables expert and project lead at Alpla. “But we were certain that, if we combined our expertise in materials science, preform design, container design and systems engineering, we could find a solution for sensitive beverages like juices and dairy products. The option of using a 38-millimetre bottle neck offers particular advantages for sensitive returnable applications.”

“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.”

Testing requirements to deal with these factors were stringent, with an elaborate series of tests that analysed the interaction of different bottle designs and cleaning processes. “Among the findings: with the right combination of parameters — especially lye concentration, temperature, additive and mechanical impact — temperatures around 60°C are sufficient to reliably remove even dried protein, fat and starch contamination from the containers,” Bradshaw said.

During testing when comparing glass bottles with plastic ones, an interesting benefit was noted: where repeated washing would often visually alter the surface of a regular glass bottle, the new returnable PET bottles remained unblemished after cleaning. The PET bottles were also microbiologically identical to newly produced ones after 25 washings, meaning that these containers can see a long life on the horizon.

Thus far the returnable PET containers have been a useful and promising proof of concept, but the next stage of testing is already proceeding, with a technical field test on the horizon and with a view of bringing the product to market.

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