Is there a specific ratio of each raw materials in making a polyurethane foam?
Hi Syla,
Yes there is always a specific ratio of each raw material in making of PU-foam that will include polyol content, isocyanate (TDI) content, silicone surfactant, water and catalysts. Each and every material has distinct properties and changing ratio for even single material will change the properties. Given below, you may find a research article that better explains the conditions and how properties are changed by variant ratios.
Article Effect of ingredient ratios of rigid polyurethane foam on fo...
Cheers,
In principle, a polyurethane (PU) foam is made by reaction of equimolar amounts of a diisocyanate "O=C=N-R-N=C=O" with a diol "HO-R'-OH" in the presence of little water that allows a side reaction that generates carbon dioxide:
R-N=C=O + H2O → {R-NH-COOH }. This unstable carbamic acid decomposes:
{R-NH-COOH } → R-NH2 + CO2.
The evolving CO2 gas causes foaming in the product. If we do not want this side reaction, we can apply a "blowing" reaction or operation which effects foaming.
When polyols are reacted with diisocyanates we will get PU but there is also the possibility of obtaining a PU by reaction of slight excess of diisocyanate with a diol after which this PU is reacted with the polyol.
The choices are enormous, e.g. a) there is a low molar mass polyol that may be reacted with "aromatic" PU or b) there is a high molar mass polyol that may be reacted with "aromatic" PU . Case (a) will give a more rigid foam while case (b) will give a more flexible foam and in both cases, there is foam building reactions as stated above.
When there is chain extension and/or cross-linking, the densities of the PUs are usually slightly more than 1.
Thank you so much Muhammad Tamoor Masood Amin Shavandi
and Nizar Matar :)- Badges
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