How to quickly measure the brittleness of a plastic?

[gao7857]

For the plant, when they process the parts off the process parameters, the plastics got degraded and in my case become brittle for nylon. However many times it looks good until you test the product. Is there a quick way to evaluate the brittleness of a plastic? Thanks. The part is quite small and slim, like 5mm in width. And only moiture control seems not good enough.

 

[CoryPad]

The Izod impact test is very quick and easy to evaluate plastic brittlness.

 

[gao7857]

We have a sort of modified izod machine to test it, but we are asked to find an easier and faster way.
There are two challenges as we internnally discussed: one is that sometimes the impacted area may not represent the brittleness of the whole part; another is that the part is quite small.

Also I was wondering if annealing the parts above the Tg will help reduce the brittleness?

 

[Demon3]

You can't really do it faster for nylon. You need to leave the nylon in controlled humidity for a day or so in order to do the test. The test itself takes minutes so speeding up the test has no benefit, it's the waiting time for it it adsorb water that is the limiting factor.

As molded nylon is stiff with low elongation and impact. Once left in air the modulus halves and the elongation and impact go way up because the water from the air acts as a plasticizer.

So, all as-molded parts will be brittle and the question becomes how can you get the water into your part faster so testing can start? I'd try a pressure cooker for a short time or boil in water for a few minutes (as you said the part is small a short time should work).

Chris DeArmitt

Expert consulting & training

http://www.phantomplastics.com

 

[gao7857]

Thanks Chris for the comment. We currently add water to it. We have two tests for brittleness, one is dry as molded, another is moisturized; as the part can be used dried or moisturized. The moisturized one is fine, while the DAM parts have large variations on the brittleness, and at different sections of the part (injection flowing end region, knitting region, or region w/o too much variation). We once thought the raw nylon material was inconsistent, however the RV were close before molded. There are small RV variations after molding (you know there is a limit for certain plant to truely control the process) and the variation does not relate well with the brittleness; measuring RV in plant after molding is out of plant ability and could taking too long. So we are looking if there exist a method to quickly check it out before packaging...

 

[Demon3]

You say the part can be used dry. Where? In space? Or in a desert with no humidity?

Chris DeArmitt

Expert consulting & training

http://www.phantomplastics.com

 

[gao7857]

The part is an electrical component, Yes the part can be used in desert for solar equipment.
But with DAM we are quite aggressive on our QC, as even in desert the RH may never be zero. It is however one way we want to make a better product.
We do have product made of PA12 though, but that one is expensive.

 

[rickfischer51]

I dont think annealing will help with brittleness. If the brittleness is due to chain scission caused by hydrolysis, annealing is not gonna restore molecular weight. I think annealing generally reduces free volume. That reduces mobilty which will increases brittleness.

 

[chicopee]

Spectrophotometry was a means of detecting degradation of PVC samples at research of a major chemical plant.

 

[TomDOT]

Fastest method I can think of (per test) is a tack hammer and a skilled hand.

Doesn't solve the moisture issue, but it's a fast way to determine brittleness once your parts are conditioned.

 

[1gibson]

This is a bit crude, but can you "shave" the part in a non-critical area with a razor blade? Dust = brittle, strings or chips = not so brittle. Don't shave the same area too many times.