PTFE is not melt processable.  Have you considered using FEP instead.

Fluorinated ethylene propylene?! I'm not sure I can get this material here, but it's a very good idea specially that sintering doesn't work with PTFE. Thanks a lot, I will try to get FEP powder here, then we can see.

It's also claimed that PFA (Perfluoroalkoxy alkane) is similar.

Dear Mohamed,

As Peter said, you can't melt process PTFE using conventional methods (unless you blend it with a wax you can ram extrude it to an extent). Nonetheless,PTFE can be sintered after you have cold compacted the powder in a mold. PTFE remains a viscous gel state once you heat it beyond its melting temperature (~342C). The sintering profile is crucial for stable parts.

I wouldn't recommend sintering for the polystyrene as it would flow and not retain it's shape above the melting temperature. Unlike PTFE, it will not retain its dimensions if not pressed and held in a mold. The polystyrene you will need to melt press whilst in the mold using a hot press.

Anyway, hope this helps. Please feel free to contact me if you have additional questions.

Kind regards

Louis van Rooyen

Dear Louis,

Thanks a lot for your answer, it's very useful for me, but it means I will stop trying with both methods for PTFE and PS... It's useful to know this now as I spent already a lot of time and money trying with those two materials and it's time to take another track in my research. I will try to replace PTFE and may give another try with PS in a macro hot press.

Thanks again for saving me 

No problem.

Glad it has helped you. Please feel free to contact me if you need any additional information.

Kind regards

Louis