Polycarbonate

[Lostone]

Hi we are heating a molded polycarbonate piece to 160 C for about 20 minutes, as part of our manufacturing process. What we are finding is that the pc is becoming brittle and if pressure is put onto the part it will crack. The part is 1mm thick and supported by an insert when heated. My question to yourselves:
1: Why would this happen (part becomes brittle)
2: Would we be better off using a high heat pc
3: Is there any way of avoiding this-(annealing etc.)

Thanks for your help

 

[Demon3]

I don't think PC should go brittle under those conditions (if Pat or Pud feel differently then take their advice over mine).

Embrittlement of PC is usually caused by contact with fluids like oils, cleaning fluid, mold release agent.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Or heating above about 120 deg C in the presence of absorbed water. More likely contact with an aromatic or chlorinated hydrocarbon. It only takes a very slight exposure if it is stressed.

Also 160 deg C seems a bit low for thermoforming, so it might be introducing severer frozen in stress. From memory (I am still away from the office/Library for a few days) I think it thermoforms at about 190 deg C after drying at 120 deg C for 4 hours.

Regards
Pat
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[Lostone]

What we are trying to do is sublimate the part. The part is supported underneath throughout this process. The part is fairly flexible before the process but after the process it becomes brittle. If there are any thoughts please let me know.

 

[patprimmer]

Your terminology is really quite confusing.

Polycarbonate will not sublimate. I guess you are trying to say you are applying a sublimatic printing process where the inks sublimate and the ink vapours dye the polycarbonate.

If so what chemicals are contained in the ink or the substrate carrying the ink, then re read the second sentence in the first paragraph of my previous reply.

Also flexible relates to rigid and is measured by flexural modulus. Brittle relates to tough or ductile and is determined by nature of break. Elongation at break is often confused with brittle, so I expect you mean it has much lower elongation and it changes from tough and goes from ductile to brittle break.

If the flex mod changes it most probably is not polycarbonate and more likely plasticized PVC that loses plasticizer in the bake.

I am sorry if this sounds condescending, but we need to know what you really mean if we are to really help.

Regards
Pat
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[Lostone]

Thanks for your insight, we managed to solve our issues today. Not condescending at all, proper questions give proper answers. Since polycarbonate has micro voids in it and we were inducing additional stress on the part it opened these voids thus weakening the material. Thanks for the feedback

 

[patprimmer]

Polycarbonate does not normally have micro voids unless it is heated to much when it is wet, but if the problem is solved no need to worry.

Regards
Pat
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