I've looked at the MSDS of a couple of products for removing hardened polyurethane (PU) foam. Both contained only ethanolamine as a dangerous substance, but only between 1-5%. So I'm guessing this might not be the active substance. The Wikipedia page on polyurethane doesn't indicate any degraders (and the page on polymer degradation doesn't mention polyurethane), so what (active) substances are typically used to degrade hardened polyurethane in commercial cleaners?
I also found that some metal acetate-ethanolamine complexes can be used as catalysts for preparing PU foam. So possibly ethanolamine is the active substance or just a catalyst for removal as well. Can someone shed some light on the purpose of ethanolamine?
Example for one of the products I was looking at "Soudal PU remover SDS"; there's also a consumer leaflet for that one which might have additional hints. It's "very active", "odourless", "free of aromatic hydrocarbons", pH 10.5.