BS brittle plastic

I’m sourcing a part in China and I think they aren’t using the specified resin. I’m calling for FR3010, and ABS/PC blend. Some enclosures I have from a local supplier are very rigid but flexible. The parts I have from China are rigid, but very brittle.

Could the processing of the resin effect the brittleness? What questions should I ask to get to the bottom of this?

Thanks!

Processing temperatures will most definitely affect the final physical characteristics of any plastic part.

Think, “Honey I burnt the bacon.” Overheat those little cross-links and they’re dead.

Ask what the temperature was; compare it to the material’s spec. Of course, they can always tell you whatever they want. Unless you can be there to actually document their process, I’m not sure how you will know for sure.

Excessive heat can do it but so can contamination.

First, if you want to rule out whether they slipped in a different material, try a burn test with the good parts and bad. Compare smoke color and odor ( do it outside and don’t inhale but get a quick whiff).

Here’s a sample for comparison:

http://www.assumption.edu/users/bniece/Olympiad/Polymers/BurnTests.html

If you see green than you have chlorine contamination (find fresh air fast).

Another less toxic method is comparing how they float in cooking oil (engineering resins are denser than water).

DSC testing at your local lab like Intertek can confirm for sure

Also:
if your part has color, high heat will usually (but not always) result in darker colors so you can do a color match.

This material gets dried before molding to a moisture content of 0.02%. Polymer chains will break up above that level, so if they are taking short cuts there will be trouble

I tried a burn test. I couldn’t see a difference. I didn’t see green though and I didn’t inhale. Maybe I missed something by just looking at smoke.

The cooking oil is a good test. Do you have a reference for that? I don’t have any of the same part designed made here, so will the form of my test parts influence an oil test?

I don’t have the budget or time to do proper testing:( I’m going to see if I can get more data from the supplier.

Thanks guys…maybe I’m not insane!

Actually now that I think about it, the oil test may have been for looking for PP from PE so it may not be good for this

Another one more thing I just thought: you should see stress whitening where PC-ABS breaks. If this is not present than you don’t have the right material. If you have whitening but it looks like it’s hairline breaks, it’s possible there is
environmental stress cracking

Your parts coming in contact with solvents or adhesives would cause these problems. Look for oily spots at the breaks under a magnifying glass or microscope.

What if it doesn’t whiten at all? These samples seem to have darn-near zero flex before snapping. It breaks clean with just a little whitening near the start of the break.

weird.

Are you sure they matched the blend? You can alloy PC/ABS to pretty much any proportion, you need to double check your w/w % content of the original parts.


Non-whitening however is odd but it’s possible if the parts are brittle enough. You only get whitening in the stress fractured areas, brittle fractures won’t craze that way.

They may also have added a ton of filler which could make the parts super brittle. How do the two parts compare for size, weight, surface finish and sink? Fillers would tend to reduce your sink, increase your weight and part size, and at high proportions affect your surface finish.


You definitely need to do a close check of dimensions and part weights, that will give you some indication of where the problem is coming from.