Help needed - aging of polymers

[Boondocksaint]

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 printing, 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 parameter?
- Is there a critical parameter that I have forgot to include?

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


All help is greatly appreciated!

 

[Pud]

Read this quick because student postings "verboten" here!

Nylon 6 with laser marking pigment. Depends how thick your plate has to be...look up flow lengths injection moulding.

Alternatives to investigate: styrenics with above laser markable pigment.

So what's wrong with the usual Al laser etched data plate???? Should be good for couple of 1000 years?.

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[Pud]

Another point: If polymer rating plates do not exist already, there must be a good reason for it...

(I have never seen one, and do expect ever to see one...)

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[Boondocksaint]

First of all, thanks for your fast reply!

Second, I can't see why this would be forbidden? This is not just another random homework, its a live project, in a large engineering corporation. The final result will most likely be used on their products.

Third, on topic:

Budget is real tight and as such laser marking is not an alternative (equipment needs to be bought as well and laser is expensive).

Nah, im not actually thinking of a rating plate in the traditional sense.

More like a label, or a printable tape. For example, please see this one (not one of the ones i have at hand, it just came up on google quickly)

http://www.tufflabels.com/

The print itself is not the main issue here; it's proving the adhesive will hold.

I belive this to work, there is examples of relatively similar applications.

I just have to find an way to support my claim with 100% certanity and would like a number of some sort, but im out of ideas.

 

[patprimmer]

When I read your OP I was reaching for the red flag as a student post BECAUSE that is what YOU SAID in the OP.

Now you say it is a real world project which is allowed, however if you are marked on it or it contributes toward you achieving a qualification, then OUR work being included is kinda cheating on your homework, homework being used loosely. At this stage I am a bit unsure as to whether the question belongs here or not.

Humidity and hydrolysis is a consideration.

Yellowing from heat and oxidation or from exposure to UV light is a consideration.

It seems you are onto the difference in co-efficent of thermal expansion and it's influence on adhesion.

Many adhesives cross link. As this increases over time, the properties change, generally becoming more brittle with initially higher tensile but a lot lower elongation.

Some polymers contain additives that act as plasticisers. These can migrate and influence properties and appearance.

PE and HDPE does not respond well to adhesives.

PET is especially prone to hydrolysis and post moulding shrinkage due to ongoing crystalisation at an ever deceasing rate, but theoretically to infinity.

Nylons are particularly prone to become plasticised by water absorption.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[btrueblood]

We have used a nylon label with thermal printing, on products that see temperatures from 0 to 240 F, with condensation. The labels hold up well. Dunno the adhesive, but it is rated by the label manufacturer for the application; I would ASSume it's an acrylic PSA. The adhesive does not like any oil/grease on the substrate, which is typically steel (painted or galvanized).

 

[CheFEM]

You might also take a look at a new simulation program, called CheFEM (chemical-mechanical FEM simulation of polymers & composites).

More info at CheFEM simulation

Kind regards,
John

 

[Boondocksaint]

Hi!

First, sorry for the perhaps cocky tone in my last reply. I was not aware of the "no student"-policy.

But like I said, this is a sharp project. Grades are just pass/fail.

In light of;
the amount of work I put into this,
the fact that the subject is pretty far from mechanical (ok, some synergies exist)
comparison to thesises of already graduated former students...

... I would be utterly shocked if I fail.

I want to deliver the best technical compatible and cost-effective solution to the company, and as for my impression so far regarding this forum - is what it's all about, or that's what I belive at least.


Pat:

Thanks in particular for the feedback on plasticierz and cross-linking. I'll investigate further.
A problem is that the suppliers dont want to give complete information of materials used (which is totally understandable), but perhaps I can use general behaviour of the the plastic family and add it into my conclusions.

UV thankfully wont be a problem, since the product is used inside, and before that sealed in a box.


Btrueblod;

How long have you used the labels?


John;

I was not aware that such a program existed. I'll talk to my boss tomorrow. Thanks for the tips!


Best regards
Boondocksaint

 

[btrueblood]

Boondock,

We have used them for more than 10 years. Mfgr. is Brady, if it helps.

 

[patprimmer]

Indoors still has some UV, especially under fluorescent or even more so mercury vapor lighting.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[patprimmer]

Opps hit enter to soon.

While indoor UV is not normally a problem except near windows and in light fittings, 30 years is a heck of a long time. That is why I also mention cross linking, post crystalisation and plasticiser migration. Things that appear virtually inert for 5 years will show all sorts of issues after 30 years.

Nylon also swells as it absorbs moisture. This can stress the adhesive interface a bit. If the elongation of the adhesive decreases over time, it may delaminate.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules