I would like to learn about the way we can predict the MW of PU foam,
For example, I want to make a bulk of PU foam having density 32kg/m3. How much volume of polyether polyol and isocyanate that I need. Of course, it also comprises catalyst, blowing agent, surfactant, filler.... but I don't understand how we can calculate that when use physical blowing agent, it will diffusion out of the PU foam after processing finished.
Dear Sir;
since you are using a polyol, you will end up with a three dimentional netwok. There will be no molecular weight or you can say that the molecular weight goes to infinity, which means all chains are linked together.
To achive a desired density you have to play on the ratio of isocyanate/polyol and the foaming agent, and this will be a compromise between the structure needed and the properties.
The blowing agent leaves the foam or not depends if you have an open or closed cellular structure. Regards
I agree with A. Bouaziz. @KDH: it sounds like you're trying to figure out how much water & physical blowing agent to add. Water will react with isocyanate to eventually form CO2 gas, or else evaporate into steam. So every 1 mole of liquid H2O = 1 mole total of CO2 gas and H2O gas (steam).
Your foam density is simply mass of formulation divided by foam volume. You can estimate the total foam volume very well from the ideal gas law (V = nRT/P) , if you know your maximum reaction temperature (varies a lot -- also, your physical blowing agent acts as a refrigerant and counteracts the reaction exotherm, thereby lowering the final temperature. In many cases, without physical blowing agent, your final temperature can be from 120 to 200 degC depending on your water content). P can be estimated to be 1 atm (if you're at sea level -- will be lower as you go up in elevation, especially in mountainous areas). So the rest is straightforward math. Just keep in mind that temperature can go up really high as you add more water, so that you need to be very mindful of fire safety when you do this.
Some additional useful links on this topic are attached below.
https://dow-answer.custhelp.com/app/answers/detail/a_id/5139/kw/water%20foam/related/1
Yes, PU-foam is essentially one molecule.
You cannot simply predict the foam density by the amount of blowing agent and water added, as you will always have some loss. That's why the manufacturer should give some instructions on how much blowing agent and water to use to get the desired density.
The molecular weight of a PU foam is infinite because the PU in a foam is a crosslinked material. It is made from more than two functional monomers. This leads to complete gelation in the polyaddition reaction.
Predicting the molecular weight of the PU foam is very difficult as the urethane polymer corsslinked to one big molecule and polymer concentration become very low. However, if you really need the molecular weight to calculate another property, you have to predict it based on DP or PDP. This is only can occurs via simulating the PU reactions to get how the concentration of all the recipes are changing with time. You can read some usefull papers that use simulation to get PU foam viscosity.
Check this paper:
Fu, Z. and G.J. Suppes, Group contribution modeling of viscosity during urethane reaction. Journal of Polymer Engineering, 2015. 35(1): p. 11-20.
Dear all,
if you want to get an idea on the kinetics of polyurethane formation, you have simply to start the polymerization with a diol and a disocyanate, but here the diffusion controlled kinetics is roughly neglected, since the diffusion parameter is more pronounced in the case of a 3D (network or crosslinked) system compared to a 2D (linear) one. Regards