How to Differentiate PVDF from PTFE Engineering Plastics
Have you just discovered that two batches of engineering plastics have lost their tags and you cannot tell PVDF from PTFE? Read on and discover some of the identifying characteristics of these two engineering plastics. Use this information to identify which batch is PVDF (polyvinylidene fluoride) and which one is PTFE (polytetrafluoroethylene).
Cut off a small piece of the two engineering plastics and burn those plastics independently in a controlled environment so that the toxic fumes generated don't pose any health hazard. You will observe a luminous yellow flame when one of those plastics is burning. That plastic is PVDF. The flame on this plastic will be extinguished the moment you remove the fire that was making it to burn. PTFE doesn't burn so you will not see any flame coming from it.
Another way to distinguish between those two plastics is to observe their colour. While both are opaque, PTFE has a radiant white colour. PVDF is milky white in colour. The easiest way to tell them apart is to place them next to each other. The one that looks brighter/radiant is PTFE.
PTFE is very easy to deform due to its inherent softness. It is therefore possible to make a positive identification of PTFE by running your fingernail on its surface. The plastic will show a score mark where your fingernail made contact with it. Repeat the same procedure with PVDF. You will not observe any score mark on it because it isn't as soft as PTFE.
Service Temperature Tolerance
You can also subject the two engineering plastics to progressively higher service temperatures in order to observe the point at which their structural stability begins to change. PVDF will be the first to show signs of degrading under the elevated temperatures. PTFE will remain stable much longer under those high temperatures. The same trend will be observed when the two substances are exposed to temperatures that keep dropping below freezing point. PVDF will be the first to show signs of failing while PTFE will retain its dimensional integrity for much longer than its counterpart will.
Record your findings for each of the two plastics above as you compare them on the attributes discussed. You will then come to an accurate identification of each of the two batches of engineering plastics. However, you should remember that the plastics may not display the behaviours described above in case they were modified using various additives in order to alter their performance characteristics. In such a case, consult experts so that you avoid mistaking one plastic batch for another.