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Topic: Aging of polymers  (Read 3125 times)

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Offline Boondocksaint

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Aging of polymers
« on: November 19, 2012, 06:02:35 PM »
Hey,

I'm a Swedish mechanical engineering student currently writing my bachelor thesis.

One of the topics included regards aging of polymers. My knowledge of chemistry is still limited after weeks of intesive studies, and that's why I'm turning to you guys.

The problem is like this;
I am to suggest a cheap replacement for aluminium rating plates fastened on electrical equipment.

Seems easy enough, ya?

Well...

Problem 1:
The thing is supposed to last for 30 years, in service temp of 55 °C (131 °F), with humidity 50-85%.

Problem 2:
I cant use bolts or screws. It has to be an adhesive of some kind.

Problem 3:
Cost restrictions forces me to use Thermal Transfer, meaning the rating plate has to be of polymeric material.

I've been in contact with numerous well-renowned suppliers and got about 20 different alternatives to choose from, that should work according to them. I just have to prove it somehow, and I still haven't found a critical parameter that allows me to say "this is great stuff".

Im currently comparing the following:

Adhesion (N/mm^2)
Recommended service temperature
Thermal expansions coefficient
Swelling
Yield strenght
Tensile strenght
Strain
Price
Reference applications (i.e. if there is documented long-term use on laundry machines, motors, gearboxes etc).

I'm also performing a standard arrhenius-aging test, measuring loss of adhesion. I doubt it will give much info though, since I only have a few weeks and not the months or years required.

So, my questions...
- Should I remove some parameters?
- Is there a critical parameter that I have forgot to include?


Materials used are mainly HDPE, PE, PET, and some PVC (though this seems crappy). Adhesives are all PSA-type, mostly acrylic, but some rubber-based adhesives are included.


All help is greatly appreciated!
« Last Edit: November 19, 2012, 06:18:25 PM by Dan »

Offline MOTOBALL

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Re: Aging of polymers
« Reply #1 on: November 19, 2012, 09:27:08 PM »
Is adhesion the primary factor ?? If not, then I would think that chemical stability under the severe service conditions (55 C/ 50-85 %RH) might be an issue.

e.g., poly-esterified materials may be susceptible to hydrolysis, while oxidation of >C=C< bonds may also change physical parameters.
 
Do you have access to the Kirk-Othmer "Encyclopedia of Technology", which may have relevant information ?

Offline Boondocksaint

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Re: Aging of polymers
« Reply #2 on: November 20, 2012, 02:13:16 AM »
Hm.

To clarify, I inted to use a label of some kind, rather than a rating plate in the traditional sense. The suggestions that I've got my hands on are as per listed materials.

Hm, not that I'm very good at chemistry (and trying to sort out all the information there is seems to take years), but why would the "plate" itself be the issue?
I mean, max service temerature is typically +120 C.

I think the main issue is the label falling off, and as such the adhesive is the weak part. If I'm wrong, please explain why  :)

Anyways, I've gotten very mixed responses when asking around bout this. Retailers typically say "not possible", whilst the manfacturers say "sure, no problem".
Problem is that no one seem to be able to prove why it will work.
Neither have I found an idiot-proof number, other than actually using the stuff for 30 years / performing an acc. aging test (which still would require years).

Offline MOTOBALL

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Re: Aging of polymers
« Reply #3 on: November 20, 2012, 08:51:56 AM »
I'm a little confused==your post is titled "Aging of polymers", which led me to believe that the polymeric label itself was the issue.

However, if the adhesive itself is the concern, you may still need to consider possible chemical degradation of the adhesive.  I have no knowledge of adhesives, so would again suggest the Kirk-Othmer series.
Good Luck !!

Offline Enthalpy

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Re: Aging of polymers
« Reply #4 on: December 27, 2012, 10:08:20 PM »
Polymers do age, and  rather quickly. A "service temperature" is not supposed to be survived for 30 years...

Each polymer has its own weakness. UV light is bad for most compositions and is available from Sun, fluorescent light... Look at a plastic bag in Nature: after 3 years of Sunlight it's in pieces. A Polyimide film would resist UV and heat, but acids not really, and hot water over time is doubtful; worse, it may be more expensive than aluminium.

An aluminium plate is really cheap, a pair of rivets as well - probably cheaper than the glue.

I have approximately zero point nothing confidence in the glue. Over 30 years lukewarm is a bad challenge.

You say 30 years, but I've seen so many motors and generators in useful service after 50 or 80 years - I coudn't imagine their nameplate with all operation data gets lost. Their doc is long lost and the manufacturer closed, you know.

-----

Could you propose slightly different methods? Like:

Produce a stencil once, use it to pattern a very good paint or ink, through it, on the motor. Say, the paint used for model aircraft, or a better one.

Put an area of very good paint on the motor, use a laser to burn the text deep in the paint. Such lasers +drive +software exist for wood.

If only writing on the aluminium plate is expensive, I'd anodise said aluminium plate black uniformly (buy it anodised) and burn the text with a laser of short pulses, which will evaporate only the shallow surface, and preferably the black oxide.

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