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  • Which plastics are microwave safe?

    Discussion in 'The main mechanical design forum' started by kuwakuwa, Mar 26, 2011.

    1. kuwakuwa

      kuwakuwa Member

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      Hi guys how is it going,

      I have a plastic cookware idea that I'd like to try out on Kickstarter, but have had a pretty difficult time figuring out which plastics are microwave safe. Below is the best info I was able to find. But based on that info, it seems like I can't use any plastics without the worry of health concerns.

      I was wondering if any of you have designed plastic cookware before and are familiar with the plastics, processes, and approvals required to bring something to market.

      I plan to go to Target/Walmart later today to buy some microwave safe plastics and see what they are made of, but I'm concerned that they may have some sort of proprietary additive/process that allows them to be considered microwave safe.

      Thanks!

      Info from http://www.scn.org/~bk269/plastics.html
      Type 1 - polyethylene terephthalate (PET) May be safe if marked "microwave safe", although some recommend against food contact when microwaving.
      Type 2 - high density polyethylene (HPDE) May be safe, although some recommend against food contact when microwaving.
      Type 3 - PVC, polyvinyl chloride, vinyl Do not use in microwave. Also, PVC often contains bisphenol A (BPA)
      Type 4 - low density polyethylene (LDPE)(mixed commentary regarding microwave safety)
      Type 5 - polypropylene - May be safe, although some recommend against food contact when microwaving. "Type 5" are the most commonly labeled "microwave safe". Despite this, I have observed "Type 5" containers with partially dissolved surfaces, apparently from microwave use.
      Type 6 - polystyrene, styrene, polystyrene foam Not heat stable. Do not use in microwave.
      Type 7 - polycarbonate; "other" (can contain bisphenol A (BPA); most polycarbonate contains bisphenol A)
      Do not use in microwave.
       
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    3. Brian Hill

      Brian Hill Guest

      My guess is none. If the right amount of fat or oil is set on anything in the microwave, it will focus most of the radiation on that point. That point can easily get beyond 500F. Fortunately, most of the time, that radiation is spread out to enough fat and water that things simply get warm. Superheated areas quickly dissapate to colder areas.
      Maybe thermoset plastics would survive?
      My next guess would be that no regulatory agency would actually say approved for the microwave.

      For comercial and consumer food goods, the NSF does a lot of certification. (National Sanitary Foundation) However, you don't need to go through them to be sold in a store. (Turkey fryers have no regulatory approvals that I have seen. They are insanely dangerous.)
      In general, NSF uses FDA anaylsis to determine the chemical suitability of plastics. If you search through the NSF.org databases, you can see different materials are approved under different conditions. Of course it costs $$ to be listed, so most OK plastics aren't listed.
       
    4. AndrewNew

      AndrewNew Well-Known Member

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      I think it will depend on the particular grade of material you choose. It is not even as simple as specifying, say, polypropylene over polyethylene, since one manufacturers polypropylene might have a different composition to anothers. As another example, not all polycarbonates contain bisphenol-A (although most do, and you are right to be wary, the EU has just outlawed polycarbonate produced from bisphenol-A for infant feeding bottles, as have Canada, not sure about the US). I would suggest contacting a reputable polymer supplier (try Exxon Mobil or Dow) for their advice. I've just done a consultancy job looking at polymer safety for a food packaging application, and Exxon Mobil in particular were very helpful. Their Southampton number is 023 8089 2511. My guess would be some kind of polypropylene but I have been wrong on many occasions before!

      Hope this helps.

      Cheers

      Andrew
       
    5. kuwakuwa

      kuwakuwa Member

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      Thanks guys much appreciated.

      I went to the local Target to collect microwave and dishwasher safte container. They were all Polypropylene.
      However after doing some testing, I quickly found that like Brian was saying, the PP would melt if I put any fatty substances in the tray. This was kind of disturbing since I could see lots of people doing this..

      Great advice on contacting the plastics vendors. I'll try that out.
      I'll also look into thermoformed materials.. all the containers were injection molded.

      Lastly just for fun, I have some temp strips on order from McMaster Carr. Gonna microwave them with different foods to see how hot it gets.

      Thanks!
       
    6. AndrewNew

      AndrewNew Well-Known Member

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      I think you mean thermoset rather than thermoformed. My understanding of thermoforming is that it involves the application of heat to a thermoplastic to soften it sufficiently that it can be drape or vaccuum formed - typically at relatively low temperatures. Not ideal in your case!

      There are some exotic thermoplastic polymers such as PEEK and PAEK that have heat deflection temperatures > 150°C but they are $$$$!

      You could look at phenolics - they are thermosets and can be used to make the handles for cooking utensils that go in the stove, but I'm not sure if they would work in direct contact with the food.

      Cheers

      Andrew
       
    7. maniacal_engineer

      maniacal_engineer Well-Known Member

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      Melamines are no good they get really hot and destroy themselves in a microwave. I seem to recall a similar effect with phenolics, but you might want to test it to make sure.
       
    8. kuwakuwa

      kuwakuwa Member

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      Thanks for the correction. I actually did mean to say thermoforming, as I was not familiar with thermosetting. Looked it up on wikipedia so now I'm informed. :D

      In anycase, that PEEK stuff looks awesome. Gonna call them to see what the general cost is.. Although it might be expensive, I'm figuring it can't be more than the option of going to a pyrex type glass material. We'll see.

      PEEK 150G Easy Flow
      http://www.matweb.com/search/DataSheet. ... 108a771fcf

      Melt temp of 650°F!? Thats awesome.
      Thats gonna be one hot mold and barrel though. I wonder if that requires an oil cooled mold.. or if you need any cooling at all.
       

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