April 9, 2010

Assessing the flaws in ziplock bags

Posted in Modelling, Prototyping at 9:25 am by Kilo

Many of the issues of using a ziplock bag as a travelling case for liquids were well known to us from many hundreds of thousands of air miles travelling with them in hand luggage over that past few years:-

  • splits in the plastic
  • contamination of medicines that break open
  • accumulations of gunk from various small leakages
  • weak closure strength
  • the need to constantly replace the bag
  • lack of organization inside the bag

But during the design process we also tested a few quite strange areas of weakness, such as the ability of the ziplock sandwich bag to withstand being frozen full of water. When water freezes it expands in volume by about 9%-10% – with a force that has literally crushed the hulls of ships. Below you can see a picture of Sir Ernest Shackleton’s Antarctic expedition ship ‘Endurance’ being crushed by expanding ice, even though the ‘Endurance’ was one of the strongest wooden ships ever built, with a hull that was up to 75cm thick.

We wanted to know what would happen to both a ziplock bag and a Jellypod if someone choose to use it for making large ice cubes. So we filled one with water and put it in the freezer. Below you can see a photo of the ziplock bag full of an icy block – and the zipper popping open as the water freezes and expands into ice.

Strange but quite interesting tests like this gave us some ideas of the properties needed in a Jellypod, and also gave us some good ideas for differentiation and marketing of Jellypods. In later blogs we’ll show you some other interesting tests we carried out – some of them were quite destructive and fun to watch!


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