Soft PU foam help

Hi Folks,
I've just started a PhD, which initially involves the synthesis of some
soft viscoelastic polyurethane foams. However, I've not been having
much luck. I've been trawling through the literature for formulations
of such foams but anything I've found has been vague with respect to
specific formulation ingredients.
I've made a few 'water blown' foams (I hope this is the correct
terminology) using MDI prepolymer, Voranol polyols, DABCO and DBTL
catalysts and a silicone surfactant. The foams so far have looked
promising initially but ended up being sticky and in some cases they
looked like they collapsed?? - so I'm going back to the drawing board.
My understanding is that for a soft viscoelastic foam I need a polyol
with a high OH value and an average functionality of about 2.5.
However, I have no Idea how molecular weight relates to softness. I
would really appreciate it if someone could help me understand the
fundamental relationship between the foam additives and softness of the
foam (while still retaining viscoelasticity). Any suggestions for a
formulation for a really soft PU foam ?
I know that I haven't quantified what I mean by 'soft' but I've been
looking at PU earplug materials, which are close to what I need but I'd
like to make a range of softness even softer than the PU earplugs.
Anyways, I'd really appreciate it if someone could help me out or
recommend appropriate literature sources or textbooks.
Kind regards,
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Have a look a the patent literature. You should be able to find a lot of real-world examples with detailed formulations there.
Be aware that patents do not always tell the truth.
Regards, Oliver
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Oliver 'Ojo' Bedford
It's fine that you want to hop in, start mixing and see what happens, but keep in mind that six months in the lab will save you a day in the library.
Just for the record, I don't seriously believe in just doing research until you find the answer, anymore than I read the entire manual for software before I do anything with it. But I also don't believe in never looking at the manual either. It's an iterative process. Having some experience helps the tips in the manual come alive.
That said, you are seriously overdue for a trip to the library especially since you are a PhD student! I'm not going to waste time insulting you. Insert your own favorite insults here and let's move on.
Polyurethanes Chemistry and Technology by Saunders and Frisch is a classic.
John Aspen Research -
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"Turning Questions into Answers"
Opinions expressed herein are my own and may not represent those of my employer.
Reply to
Sounds like your stoichiometry is off. Have you looked at slight changes in your composition of polyol to isocyanate? I'm not a urethane chemist but my understanding is that for soft foams you need a relatively long flexible polyol.
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Larry Effler
Hi! I just finished my B.E in polymer engineering from Pakistan. Well could you go into the stabilization of the foams while the curing period is going through, if you manage to keep the cells stable during the curing period the foam would not collapse.
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In addition to the old Frisch/Saunders book already suggested, there are 2 more recent books on this topic: The Polyurethane Handbook by G. Oertel and the Polyurethane Book by D. Randall/S. Lee (Wiley), the former being a more detailed reference book, while the latter is more up-to-date in several technology areas. However, none of them discloses viscoelastic foam recipes which are usually kept secret by the raw material suppliers (Dow Chemical, Huntsman, BASF/Elastogran, Bayer, Mitsui, etc...) and some clever foaming companies. Some patents may give clues, but the raw materials used in examples are difficult to find commercially, especially in small quantities. Most commercial recipes for slabstock use TDI, but there are exceptions like some Recticel foams which use MDI. In moulding MDI is preferred, but there are also exceptions like Tempur foams which are based on TDI. The selection of the isocyanate is not really critical (unless one uses a prepolymer) and the same applies to additives like catalysts/surfactants . The selection of the mixture of polyols (with high and low Tg) is much more critical to obtain a suitable DMTA profile and relaxation properties. A traditional and simple example is given in GB2138012, but there are many variations possible, depending on the targeted properties. Some recent developments use EO rich polyols (or polyols with EO in blocks in their chains) which have higher Tg than PO rich polyols. Good luck...
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