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  1. #31
    So, then....
    Which flexible filament should be used when making a flexible cup to drink from?
    Are any "food-safe"? (Just thinking here of all of those water bottles that are now labeled as "BHA/PBA free")

    Quote Originally Posted by pyrophreek View Post
    In regards to why TPU is not recommended for long term immersion in water, a better understanding of the polymer chemistry is needed.

    From Wikipedia:

    What this means is that when you submerge the TPU in water, water molecules (which are polar) will slowly intercolate into the polar "crystals", and serve as lubricant between chains. This will cause the TPU to become swollen, and cause a loss of the elastic recovery response. How much of an effect this is depends on the exact chemistry of the specific TPU formulation, as they vary greatly.

  2. #32
    Super Moderator curious aardvark's Avatar
    Join Date
    Jul 2014
    I'd use polyflex.
    it's as safe as everything else - which is to say that it's down to the individual to take reponsibility for drinking from a 3d printed cup.
    But shouldn't taint the water as much as a tpu based material.

    Actually there IS a safe flexible material that is not only anti-bacterial but also anti-viral.
    No it's not certified - but it'll kill any microbes that come minto contact with it.

    reprapper techs flexible pla with copper.
    Copper kills any and all microbes that come into contact with it.

    Not sure how it would effect the taste of any liquid - but it would be safe from a bug point of view.

  3. #33
    Engineer ralphzoontjens's Avatar
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    Nov 2013
    Tilburg, the Netherlands
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    TPUs can be FDA approved, but I haven't seen any filaments so far with the approval. Would be interesting to know.

  4. #34
    Technologist American 3D Printing's Avatar
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    Jan 2014
    Evergreen Colorado USA
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    Quote Originally Posted by ralphzoontjens View Post
    TPUs can be FDA approved, but I haven't seen any filaments so far with the approval. Would be interesting to know.
    There is no such thing as FDA "approval" for a material per se', however medical devices can be cleared for marketing through the 510(k) process for class II devices and with clinical trials for class III devices. When FDA reviews a device for marketing, materials of manufacture are among the characteristics that are evaluated by the FDA reviewer. In the case of pharmaceuticals, both the formulary and the manufacturing process are evaluated, including materials that may come in contact with the pharmaceutical during manufacture and packaging.

    There is however a list FDA-approved of materials called "GRAS" which stands for "Generally Regarded As Safe". These are for food ingredients and additives rather than materials such as TPU.

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