Can any one help me to Know the reason of my problem which relates to the TPU( thermoplastic polyurethane): I synthesized TPU by prepolymer techniques and during casting I recognized a formation of many bubbles that remained after casting inside the TPU film and I could not know the reason, a lot of thanks of any help.
If you're casting from a solution, slowing down the solvent evaporation (lower temperature, or storage in a semi-closed container during drying) may help. Furthermore, vacuum degassing of the solvent may help to remove dissolved gasses. You may try this as well for the solution of the polymer, but there might be foaming issues in this case. Good success!
The micro bubbles can indeed be trapped solvent due to the too high cooling speed.. Slowing the cooling speed down can reduce it.
Another issue can be the fact that you use a convection oven. If you do so then shall the outer shell be hardened everywhere and capture the material. you can avoid this by using a hotplate ( the material is then casted from bottom to top).
Also can air pressure differences create them. To avoid these is needed that the pressure in the oven is maintained at the same level during casting.
Depends when you first notice the bubbles. Are they present in solution prior to dispense? Also, what size are the bubbles? If they are relatively large (20-100um) the issue could be casting speed and interaction with low dispense volume. Try increasing dispense volume and reducing casting acceleration time.
when we dissolve a polymer in solvent then during stirring air may entrapped in viscose solution. So before casting solution should be kept in vacuum oven to remove any bubble formed formed.
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