With waterblown system for rigid closed-cell polyurethane system, water reacts with isocyanate to form CO2 and this gas caused bubble on the foam surface. The surfactant dosage was tried to 2 and 3 parts per hundred polyol. Please kindly help, any suggestion would be highly appreciated.
There maybe several reasons:
(1) What is the temperature of the mould? It should be in the range of 45°C
(2) What is the amount of over-dosage (pressure in the mould)
(3) Reduce the amount of stabilizer to the typical amount of about 0.2 % of the polyol component
(4) Maybe adding a physical blowing agent (e. g. pentane or pentafluor butene) might be helpful
Controlling difference of temperature between mould and matrix glass transition is essential.
Thank you Dr. Gerhard and Dr. Valle. The cup/mold wasn't preheated since it isn't PIR, just at ambient room temperature and didn't measure the exotherm temperature. The pressure in the mold is also at 1 atm since it has vented with 5 holes. The surfactant dosage is 0.3 pphp and it is requested for only using water as the blowing agent for longer reactivity (creamtime 50 secs, while gel time 250 secs).
I have seen few people do vacuum to suck all air out during the process by a method called vacuum degassing. Check this you tube below, it might not exactly related to what you are doing but the concept is worth it to try.
https://www.youtube.com/watch?v=l7WRGfnJQaM
Thank you Dr. Mohamed, I also have the same thought, but this might not be applicable for my case.
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