Ageing of Epoxyde Resin

[davidmoul]

Hello Evryone,


I'm trying to plan ageing test for an epoxy resin (because my customer want a qualification), but I'm not really aware of that kind of tests.

I will test an epoxy resin which Tg is about 80°C, which will be used at 120°C (above Tg). I'm thinking ageing it at 180°C, even if the maximum recomanded temperature is 155°.

- Is this maximum temperature recommanded to prevent thermal ageing, or do you think it is possible that another degradation mechanism appear?

- Important parameters are thermal expansion and mechanical properties (Young modulus). Do you think these parameters will vary in a consistent proportion (Sorry, I'm not well accustumated with polymers).

- Is Young modulus relevant in term of polymers?

- Do you think that I need to test ageing above and under Tg? (tests to identify different thermal ageing mechanisms depending on the microstructure of the polymer).

- Do you think I need thermal cycling (nominal temperature will vary betwwen ambiant temperature and 120°C).

thank you for your precious help!

 

[Demon3]

Hello. Accelerated ageing of polymers is a common test. Even though the results may not agree at all with reality, oven ageing some kind of testing must be done so we have to accept the uncertainties associated with it. The most common test for oxidative stability is oven ageing. You place the samples in an oven for a period (usually some hundreds of hours) and measure the mechanical properties before and after. Modulus is not a good indicator. The properties that degrade will be elongation to break and tensile strength. Other tests you could use would be impact resistance and carbonyl index (the intensity of the carbonyl peak at 1800 cm-1 inthe FTIR is proportional to the amount of oxidation). I am only really familiar with ageing of PP, you should look up the temperatures and times used for epoxies.

Be aware that small amounts of antioxidants such as hindered phenols, HAS etc can dramatically improve the results by protecting the polymer.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[davidmoul]

thank you for your response.

In fact, I have another question: Modulus is not a good indicator, ok. However, this is the functional parameter of my resin here. The resin won't be sollicitated in tension, but only in compression (encapsulating resin).

Knowing that, do you think that I must preferrably work with the tensile strenght?

In fact, I think their won't be too much ageing of my polymer. But the customer want some qualification. I guess I'd probably better test functionnal parameters right?

 

[Demon3]

Does the customer want modulus? It seems to me that is unrelated to encapsulating performace. I suggest you measure compressive strength is that is relevent for your use situation.

If you use an epoxy above its Tg then it will keep curing and become more stiff and brittle. This is a chemical change of course and not oxidative degradation. Oxidative degradation won't affect modulus much but the post curing may.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[davidmoul]

Thank you, it become clearer and clearer for me... in fact, the idea was to obtain the Young modulus and to calculate some deformation of the thin metallic structure after ageing via FEM simulation. Cause the functional parameter is the deformation (caused by the thermal response of the resin, and the stress).

Getting Thermal expansion and young modulus after ageing would give me a way to calculate this theoretical deformation and then to determine if the thermal ageing of my resin is relevant or not. I don't know if I'm really clear. I know thermal ageing is not really well representative of what I could expect in reality, but that's the only way I can see to find a relevant criteria.

Because measuring the compressive strenght of the resin would give me a valueable way to estimate the ageing of the resin, but the question is then how to decide if the results are satisfying or not? An idea about it?

I know, I may have stupid questions, and I have to thank you for your precious help.

 

[rodneybennet]

Hello David Moul:

Especially if the epoxy structure is - besides loaded mechanically or stressed by temperature - exposed to chemicals (like water, acids, etc.), I would like to refer to:

http://www.composite-agency.com/materials-forum.htm

They are specialized in tests and simulations of mechanical retention under stress and chemical exposure.

Thanks,
Rodney