MDF is a challenging product to make, it uses more glue than other products which only need to layer wood together, etc., and therefore has the biggest problem with formaldehyde emissions. There are also soy based glue alternatives, but possibly only used in plywood, not MDF, so far. Offhand I would not be happy about having 60 pounds of MDI or whatever in my door. Offhand PVA sounds more interesting to me, as far as less toxic breakdown products (this is just an offhand reaction, I've done no actual research), but in a list of NAUF products only one used MDI, and none used PVA. The most commonly used No Added Formaldehyde options are MDI (methylene diphenyl isocyanate) and PVA (Poly Vinyl Acetate-this is NOT a PVC). PF emits considerably less formaldehyde than UF. This is a red and black colored substance, used as a substitute for UF in outdoor products because it has better moisture resistance. Starting with the No Added Urea Formaldehyde (UF emits the most formaldehyde) the first alternative is Phenol Formaldehyde (PF). Meanwhile, other stacks of plywood went from barely tolerable to totally unacceptable in smell. It had very little smell, but from what I could tell it had a slight milk carton smell. After finding this out I went down to the closest Home Depot store, and there it was, a beautiful piece of Red Oak plywood with Purebond.
Wonder of wonders this premium product is sold at Home Depot, and they may be the best place to find it. Soy adhesives are also used in milk cartons because of their safety.
No formaldehyde or isocyanate based adhesives. This uses soy based adhesives exclusively. Purebond Hardwood from Columbia Forest Products. I've found something that may just be the ticket. That is a 65 STC door assembly, and would not be a good match for a 29 STC door.) (*What almost predictably led Eric to this conclusion was my confession that I was attaching the new door to a wall with 5 layers of drywall, green glue, and whisper clips. My friend doesn't think I should spend so much money (even though I haven't begun to admit how much this will actually cost). I personally feel this is one of the more important home upgrades, especially for people like me with weird hours and audiophile habits, and a friend with pets. I could use a regular IsoDoor for both Queen's and King's rooms, yielding excellent acoustic separation and excellent isolation from the living room stereo. Both he and I agree that the IsoDoor Basic would probably deliver disappointing performance.* It's not much more massive than the hollow core doors I already have. Good News! Eric Pollard of Sound Isolation Store has agreed to check out other options than MDF as the core of a regular IsoDoor.