After much work on design and R&D, Sipa of Italy has created a PET water dispenser bottle that collapses as it becomes empty, reducing its size for easier recycling.

There is a growing trend for single-use PET bottles used on water-coolers because they can weigh as little as 330 g, compared with the 650 g weight of a multi-trip PET bottle. “This saves on materials of course, as well as on transport costs,” said Sipa.

The blow moulding technology company worked with various customers to develop designs for single-use water-cooler bottles which collapse on themselves as neatly as possible – a challenge that is not as easy as it sounds.

“Bottles often collapse in an irregular manner, leaving lots of space inside even when they are completely empty of water,” said Sipa.

It used Finite Element Method (FEM) analysis on computer simulated collapsing sequences to find the buckling mechanism that would best suit the client’s requirement.

“FEM analysis accelerates the time of investigation and reduces the number of trials aiming at the correct solution,” said Dino Zanette at Sipa. “It also aids in determining a minimum weight at which the collapsing mechanism is still functional.”

Sipa tried out different bottle shapes, both square and round, which were analysed along with the shape of the ribs and base.

“Graphs of volume vs. pressure and base centre displacement vs. pressure, together with photograms of the simulation, helped the Sipa experts to better understand the collapsing phenomena and how to modify the bottle structure to get the best performance,” said the company.

It also made prototypes to verify the designs. The company has carried out trials to prove the reproducibility of the collapsing mechanism that was studied during the development stages.

“So now, fully self-collapsible containers that require the application of no external mechanical forces to deflate are in industrial production. This makes the job of collecting them for recycling or simply putting them in a recycling bin much easier than before,” said Sipa.