How to identify polycarbonate
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  1. #1
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    Default How to identify polycarbonate

    I picked a couple of pallets of materials, mostly jig plate, at a bid sale recently. There are two labeled plates of black polycarbonate, 3" x 12" x 24", and 2 unmarked pieces 2-3/4" x 24" x 24". They look like the same material to me, but I'm wondering if there is a way to determine if they are in fact polycarbonate?

    And I know this is a dumb question, but I'm wondering what polycarbonate might be used for? I know it's much stronger and solvent resistent than acrylic? Does it machine reasonably well?

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    Take a small area and hit it with some acetone, if it crazes when it drys it's polycarbonate.

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    I'm wondering what polycarbonate might be used for? I know it's much stronger and solvent resistent than acrylic? Does it machine reasonably well?
    Males good tuff "window glass"

    Machines great

    These oil sight "glasses" made from such - still look the same after being installed in 2004
    Attached Thumbnails Attached Thumbnails dcp_0652.jpg  

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    The way the professionals do it is to slice off a thin chip, light it on fire, blow it out and smell the smoke.

    Keep in mind many grades of polycarbonate will disintegrate with any oil contact, even just from your skin. When polycarbonate eyeglass lenses form cracks around the nose bridge this is most likely caused by skin oil.

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    Its stress that cause polycarbonate to craze. As long as there is no stress, it holds up well. The smoke test is the way I have always seen it identified.

    Tom

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    Google: plastics identification chart
    Ken

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    Quote Originally Posted by TDegenhart View Post
    Its stress that cause polycarbonate to craze. As long as there is no stress, it holds up well. The smoke test is the way I have always seen it identified.

    Tom
    Polycarbonate is a poor choice for chemical resistance. One good clue is how easy it is to glue to, many chemicals will attack it. I used to be involved in injection molding, art to part, and used a fair amount of polycarbonate in very structural parts making stuff for sailboarding. Most of the items we made from polycarbonate were under a lot of stress while in use and I never saw any crazing or stress fractures, ever.

    One story that sticks in my head about this was told by an applications engineer. It was about some plastic covers made for grocery cart handles. This is a very low stress application, it just covered the metal handle. Problems were noticed in the first month and about 6 months later they all had broken off, even the ones that had very little use. Granted not all grades of polycarbonate are this sensitive to chemical attack but enough are that it is a very valid concern.

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    Thanks for the replies.

    I tried the acetone test on the 2 blocks, along with a piece of clear Lexan. The labeled block and the lexan were affected in a similar way by the acetone, while the mystery piece was totally unaffected.

    Then I took a blockplane and made some shavings off the corners. the shavings looked and felt very different. The polycarbonate burned well with black smoke, and kept burning on its own. The mystery stuff burned after 5 seconds in the flame, with a yellow flame and almost no smoke. It melted, leaving drips.

    So it's clear that I have two different plastics, but how to identify the mystery stuff? It's shaving was more translucent and stronger (less brittle) than the poly.

    edited - more info from the burn test.
    Attached Thumbnails Attached Thumbnails img_1684.jpg   img_1687.jpg   img_1688.jpg  

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    Look at post#6
    There are several identification flow charts, like this one:
    http://www.consultekusa.com/pdf/Tech...20chart%20.pdf
    They walk you through elimination steps.
    Ken

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    The burn test is so you can smell the smoke, you tell what plastic it is by the smell.

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    That one looks great Ken, thanks. Gotta get someone in here with a sensitive noise, my sense of smell is shot.

    I'll be out of the shop til friday, will test exhausively then and report back

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    The flow chart for plastics is interesting but there is a caveat. This would apply to un-filled, non-reinforced material. Particularly, the flame test for flammability. A lot of plastics are filled with flame retardants to pass U/L 94. Also a lot of industrial materials are glass or mineral filled for strength and minimize shrinkage.

    Since you say it is fixture plate, then the most common thermoplastics are glass filled nylon and acetals. After that then PTFE (teflon), polyurethane and polycarbonate.

    In thermosets, phenolic, polyester, and epoxy.

    This is not to say that the plate is not one of the other materials, the ones listed are the most common in my experience. The other materials are not common because of cost, chemical resistance and physical properties.

    Tom

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    maybe polypropylene

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    My guess from the sheet surface from post #8 pic 2 is the black polycarbonate pic 3 is black Acetal. Also polycarbonate machines ok, just sensitive to heat, and notch sensitive.
    Last edited by Bluejeep; 07-19-2019 at 03:32 PM. Reason: added info

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    hit 1/4" thick acrylic with hammer it shatters and hit polycarbonite it doesnt shatter
    .
    take acrylic sheet to sheet metal shear and try to shear it. doesnt usually end well


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