epoxy shelf life

Discussion in 'Materials' started by brendan gardam, Feb 19, 2020.

  1. brendan gardam
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    brendan gardam Senior Member

    i have 6 lts of 5-1 marine epoxy laminating resin in the shed. how long will it last , its on a shelf away from sun and heat sources.
     
  2. jehardiman
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    jehardiman Senior Member

    There is normally a gel time test, the manufacturer should specify it for resin usability. Used in the shipyard to determine the suitability of the resin on the shelf. Nominally shelf life is ~5 +/- years depending on the criticality of the formed part.
     
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  3. Richard Woods
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    Richard Woods Woods Designs

    If it starts to crystallize put the container in a bucket of hot water for a while and it will liquefy again and be quite useable. Some people use a microwave but I think that may be too extreme

    RW
     
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  4. brendan gardam
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    brendan gardam Senior Member

    thanks for the info. its only 6 months old so it sounds like it will good for a long time yet.
     
  5. upchurchmr
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    upchurchmr Senior Member

    I had some for 10+ years and it worked fine.
     
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  6. jehardiman
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    jehardiman Senior Member

    Yeah, it will still set up, but for critical applications I would make a test coupon to make sure I still had the required strength on something that old. Sometimes it matters, sometimes it doesn't. <shrug>
     
  7. upchurchmr
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    upchurchmr Senior Member

    So how will you judge the strength of the coupon?
    Do you have a testing machine?
     
  8. jehardiman
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    jehardiman Senior Member

    I don't have one in my garage, but the lab has a 600,000 lb instron machine. We did this all the time in the shipyard when making man-safe components.
     
  9. upchurchmr
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    upchurchmr Senior Member

    Better than most of us.
    What would the rest of us do?
    My work also had one (or a dozen) but I could never have gotten the use of one.
    Even before I retired!
     
  10. jehardiman
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    jehardiman Senior Member

    That is why I stressed the criticality of the part. Sure, use 10yr old resin which has lost 10-20% strength to sheath a plywood hull. But for a man-safe part loaded to 33% of the layup's theoretical strength? Testing is the only way to go. <shrug> Different horses, different courses.
    FWIW, we even destructively tested existing components as they gathered years and cycles of service or were laid up at higher/lower cure temperatures. This allowed us to pro-actively replace them before they fell below required factors of safety. Composites are not structurally sound forever. Some man-safe components now have active monitoring, but it all begins with knowing that the resin system and cure was good when you started.
     
  11. upchurchmr
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    upchurchmr Senior Member

    I don't disagree with anything you said.

    but you didn't answer.
    What is the home builder to do in a practical sense.

    On the other hand, even in my former aerospace job none of the composites we used had active monitoring - on the latest military fighter.
    And we stressed the aircraft to a higher level than 33% of the theoretical strength.

    You are making a silly comparison for this group.
    And you gave no "thumb rule" for when to throw out unused epoxy.
    1 year, 5 year, 10 year ???? For what resin?
     
  12. jehardiman
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    jehardiman Senior Member

    As I stated in my first post... manufactures gel time. Typically, the number one problem with "old" epoxy is the hardener. Because the hardener is more chemically active, most have a shelf life much, much less than the resin, especially when open. Generally at the shipyard, resin was ordered in 55 gal drums, but hardener in quarts which was tossed if on the shelf for over a year. Both hardener and resin degrade over time, generally by chemical reaction with contaminants or environment. Storing in a cool, dark, dry, enclosed space gives the longest shelf life. But there is no definitive answer about when an epoxy is no longer suitable for a specific use without testing.
    But don't believe me...try these sites ;
    Epoxy Shelf Life & Proper Storage • WEST SYSTEM Marine-Grade Epoxy https://www.westsystem.com/the-105-system/storage-shelf-life/
    Epoxy Shelf Life https://www.epoxyworks.com/index.php/epoxy-shelf-life/
     
  13. antonkov
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    antonkov Junior Member

    structural properties of epoxy are measured by several parameters, which can be quantified and are declared in the product datasheet. while tensile strength is a bit tricky to measure, the flexural strength can be tested with simple tools. for diy application the test conditions can be simplified just to compare the before and after storage results. but it also can be home tested against the datasheet, iso standard of testing is well covered and specified in the net, the sample can be in approximate dimensions as they explicitly go into the formula that gives you the modulus.
    physically the tensile and flexural moduluses are related, so testing one would give an assessment of the resin health
    20191114_210343_.jpg 20191117_163621.jpg
     
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  14. upchurchmr
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    upchurchmr Senior Member

    What did that mean?
    How are you suggesting actually doing a test?
    Testing before the storage? Who ever thinks they are going to leave the epoxy long enough to care.
     

  15. antonkov
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    antonkov Junior Member

    The flexural modulus test is about controlled breaking of a sample and measuring the braking load. Using the known dimensions of the sample and the load you get the modulus shown in the datasheet.
    The second pic shows the actual test. I took the ISO specification of the test (sample dimensions, support span, supporting and loading diameters) and 3D printed the green part to assemble it all together.
    The modulus calculation uses dimensions of the sample (not only load for a "standard sample"), therefore if you specimen turns out to be, say, 1mm wider, it will be taken care of in the calculation.

    Real life scenario: I am building part time (i.e. slow) and get my infusion epoxy from the same supplier in batches that are expected to last me a year or so, then order again. Once, I added few pales of a different (hand layup) epoxy to my order and it yielded apparently different laminate compared to my regular resin. I could tier off the peel-ply with considerably less effort than usual, so caught it empirically and luckily on something not related to the boat build. This made me concerned about quality control. I researched my options for ordering a lab test and couldn't find anything better than to run the test myself, all it takes is to break a piece of epoxy. The catch is that the sample cannot be cut or sanded to the dimensions as it will introduce scores and micro cracks, hence the wax mould for the specimens (red on the first pic).

    I broke several specimens of epoxy with and without different fillers and the load readings were considerably different, enough to assess the strength difference with numbers. To be honest, I never got to the calcs to see how close it gets to the datasheet, those questionable pales found a different application where I wasn't concerned about mechanical properties, so the test went back to the to-do list. But I am planning to get back to it and test all new incoming batches. A lab would do the very same test just with proper weight in place of the water bucket and with better looking cylinders in place of the bolts.

    Your scenario might be different, sharing this just as an option.
    Also, if epoxy is branded and is trusted to be consistent from the supplier, then perhaps you can get a quat of new resin and test it against the old one (assuming you have some large outdated amount worths the efforts)

    here is how they do it the proper way: www.youtube.com/watch?v=gDAzNjigcGU
    test name is ISO 178 (usually specified in the datasheet)
     
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