Aged polyurethane

Discussion in 'Off-Topic' started by cmartinez, Jul 9, 2015.

  1. cmartinez

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    I've been using Berg's products for many years now, and I've noticed that all of the samples (which are at least 12 to 15 years old) I own of their polyurethane chains have softened with time, and are very easy to mar and take apart by just digging my nails on them... they almost feel like hardened wax to me ...
    I hadn't noticed that before because in time I've had to replace all of the chains in my machines due to normal wear and tear. But it still leaves me thinking about the expected lifespan of any product manufactured with this material.
    Is this a normal thing with polyurethane?

    @jpanhalt, @GopherT
     
  2. GopherT

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    "Polyurethane" is an unusual material compared to most polymers. Post polymers repeat with the same unit over and over - and manufacurers achieve different properties (different 'grades') by varying the length of the chains during the polymerization. Then the polymer is processed into a part by molding, extruding etc.

    In the case of polyurethane, the basic building blocks are "isocyanate" and "polyol". These are mixed as they are injected into a mold. They react in the mold to make the polymer.

    There are 4 or 5 common isocyanates on the market but there are hundreds of polyols available (short, long, straight chain, branched chain, ...). Many, many combinations are possible. Now, to make things more complicated, the ratio of isocyanate to polyol can be adjusted to change properties - more ISO makes it more rigid, more polyol is softer.

    Also, the same material can also be changed by adding blowing agents to make foam, or catalysts to make them react fast or at low temperature. Or they can be mixed without blowing agent and with rubbery (unsaturated) polyol to make "polyurethane elastomers" like shoe soles, abrasion resistant panels, vibration dampers, and your chain.

    What I am saying is, I cannot tell you if this is "normal" for polyurethane because there is no "normal" polyurethane.

    Heat and UV light can damage polyurethanes and the degree of damage can depend on the catalysts that remain in the mixture after the reaction is complete. Obey the max speed and max load of the manufacturer of the chain and know that all polymers have a lifetime in a mechanical application. Rubber is better at tolerating. Many flexes under load than any polymer I know (that's why tires and automotive belts are made of rubber).
     
    Last edited: Jul 11, 2015
  3. tcmtech

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    Personally I want my plastics to last for their supposed 1000 year life expectancy I was told about as a kid.

    Right now I see pretty much every plastic made now starts falling apart in weeks to a few years. Same with rubber as well. I have old farm equipment with 50+ year old tires that are still holding their originally air yet I the new ones I put on my vehicles and equipment now maybe make it 5 - 10 years before the side walls weather and rot out. :mad:
     
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  4. cmartinez

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    The tyre industry is in my personal list of candidates fitting in conspiracy theories...
     
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  5. #12

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    I bought some Goodyear Polyglass tires in 1972. If I hadn't sold that car, I would probably still have the tires. :D Now that I'm retired, I have to be careful not to buy expensive tires or they will rot before I wear the tread off them. :mad:

    ps, many thanks to @GopherT for the education. He didn't have to work that hard just to help us.
     
  6. GopherT

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    Unlike you I am not retired. Therefore, I took as much time as I could to make that explanation so I could postpone my trip to work yesterday.
     
  7. cmartinez

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    Same her. My sincerest thanks for your elaborate explanation. Regardless of your motives for giving it ;):)
     
  8. tcmtech

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    I would add the fuel manufacturing industry and the typical auto manufacturers.

    Ever get one of those odd tanks of fuel that give you unusually high fuel mileage numbers for no reason what so ever? o_O

    Also ever wonder why a 80,000 pound semi truck going 65 MPH gets 6 - 7 MPG and a typical new 3/4 ton 7500 pound diesel pickup is lucky if it gets double that in the same driving conditions despite that the semi rig typically gets driven with the peddle to the floor until it gets up to speed every time and the pickup rarely ever does? :confused:
     
  9. GopherT

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    It sounds like you just solved your own problem. From now on, floor it and I am sure your gas milage will improve.
     
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  10. tcmtech

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    Yea I drove the company truck , 2013 Ford F350, like that and I can say for certain it almost got negative MPG numbers. My 1999 FOrd F250 super duty with the V10 gasser running on propane got better MPG's being driven that way. :rolleyes:

    The thing that really Po'ed me is by the book our F350 super duty service trucks had ~320 HP and most of our companies big Kenworth semis had ~425 and they could climb hills almost as well as our pickups did despite weighing about 8 times as much. :mad:
     
  11. cmartinez

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    I don't know how long ago the events you described took place... but in recent years diesel engines have lowered their efficiency in order to make them cleaner and meet current pollution guidelines... maybe that's got something to do with what you've just described?
     
  12. Hypatia's Protege

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    FWIW I can attest to the marked photo-reactivity of certain grades of said polymer to energies much above 4 eV (λ ~ 310 nm) peaking at Ca. 50 keV (λ ~ 25 pm) at which point 'PUR insulating foam' undergoes photolysis at such a rate as to effectively disintegrate "before one's eyes" (said effects occurrent at even modest 'flux densities') While I claim no 'chemical expertise', It seems reasonable to suppose (protracted) degradation occurs at even slightly ionizing energy levels (e.g. that of 'blue' light)...

    Best regards
    HP
     
  13. GopherT

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    In the polymers world, a phrase like, "sensitive to UV light" means, "not for direct sun light (unless loaded with a stabilizing additive package)".
     
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  14. cmartinez

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    Good observation... but my samples had been stored indoors all of the time and some of them inside boxes that were never opened until recently.
     
  15. atferrari

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    To improve the hatch covers' watertightness in vessels, polyurethane is sometimes used, in way of the compression bars acting against the covers' rubber gaskets. It is applied at the last port of loading when readying the vessel for sailing to destination. Maybe up to 50 days voyage, sometimes. Yes, we are far from China or Japan...

    The material that stays outside of the covers, thus exposed to everything (sun, wind, sea water and temperature variations) disintegrates easily with just little pressure of your fingers but it seems that as long you do not exert any mechanical action on it, watertightness is ensured.

    Frowned upon by classification societies. (They are right. Heavy weather could do things that you would not believe...). Been there...
     
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  16. cmartinez

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    In case you guys were curious, here are some pictures of the part that I was talking about. The first one is the chain sample, the second one shows my thumbnail being digged into one of its segments, and the third shows the deep notch that was produced in the link.

    h.jpg

    b.jpg q.jpg
     
  17. GopherT

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    You had to read between the lines but you will notice that the part producer has to mix the iso-cyanate and polyol. Any delays between mixing and molding, or improper mixing ratios or off-spec raw material all can impact the quality on polyurethanes. If something gets out the door that is not perfect, I cannot blame it on "polyurethane", it is an issue of quality.
     
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  18. cmartinez

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    Or maybe that's their way of making a product that has a limited lifespan... whether it's being actively used or not
     
  19. GopherT

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    that tactic works until their competitor decides not to do it.
     
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  20. Brownout

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    Diesels get cleaner when they raise their efficiency. That's how you get clean running diesel cars that get 45 MPG.
     
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