Using Polyurethane with a PVC covering.

1. What is a crown molding?

2. All polyurethanes (PU) are flammable. "Fire retardent" PU is less flammable than PU, but they burn fast compared to halogenaged materials like PVC (polyvinyl chloride) and Neoprene rubber (also called polychloroprene).

3. PVC is much stronger and much more rigid if is is not plasticized. Unplasticized PVC is called PVC I. Plasticized PVC is almost as flexible as regular paper and is called PVC II. Which PVC are you planning to use, and what property led you to pick PVC?

4. A common result of PVC in a fire is (a) deadly carbon monoxide (unless there is lots of oxygen); (b) carbon dioxide (which is harmless except when it replaces too much of the oxygen needed to breathe); (d) and airborne hydrochloric acid, an acid that is very undesirable to breathe.

5. PU also emits CO, CO2, etc. I can help if you do not know any manufacturers. Any manufacturer has a Material Safety Data Sheet MSDS, which will repeat what I said and give more information you MUST know.

6. PU is very abrasion resistant. I have no idea why PVC is superior other than PVC costs less.

Dear Quey,

Thanks for your response.

Crown Moulding is a decorative moulding normally used at the juncture of the wall and the ceiling of a residence or commercial establishment.

The particular product I am asking about will be manufactured for us in China.

Typically the 2 component polyurethane is injected into a sealed mould, after initial cure the mold is opened and a very thin sheet of PVC is applied to the surface using the same mould to apply the pressure for adherence.

I believe the pvc is used since it is a little harder surface than the cured PU.

My concern is that I was told that PVC along with PU in case of a fire might emit phosgene gas. Is that a serious possibility and how serious of a problem is it?

Thanks

Xn Rubber Chemist Quey: You neglected perhaps the most important one: The isocyanate moities from the urethane can generate phosgene gas, which can also be produced by the Rx of C=O + Cl2 from the PVC.

Phosgene is not an issue. Any excess isocyanate left in the part after molding would be quickly reacted by any moisture in the air. It most certainly would not be around in the case of a dwelling fire. The PVC is present to provide UV stability. Aromatic polyurethanes have poor UV resistance and aliphatic polyurethanes are too expensive to be used a base material for millwork. PVC is used extensively in the millwork industry. I am not aware of any poisoning caused by PVC during a dwelling fire. The amount of PVC present, since it is a capstock, is insignificant compared to other combustibles.

Dear Guest,

Thanks for your input. I understand you to say that the Polyurethane with the PVC cover will not produce enough phosgene to be harmful in case of a fire. Would that be a true statement?

Phogene would not be an issue with PVC only PU.

There are few (perhaps a half dozen or more) players there selling products from this sort of material at present -

see these sites for pretty well established players -

www.ultra-flexmoulding.com and

www.superiorbuildingsupplies.com

The stuff is pretty cool - nails like wood, no pre-drilling, etc. And by molding, you can design in some 3D 'sizzle' that is harder to duplicate (though not impossible) during inline extrusion. Most is pre-primed and ready for final painting for the UV protection.

Are you thinking that by going with the thermoset Polyurethane that you can avoid some of the thermal expansion issues with other competitive PVC products? The PVC portion is a thermoplastic and prolonged exposure to heat may cause some level of thermal expansion - generally 1/32" or so in a 10' piece. (10 degree rise - 1/32 change in length"). Or are you thinking that the molding process will give you "perfect joints" each time for the installer? Trying to come up with a different "pre-priming" feature etc? Be sure to work with your PVC manufacturer - even rigid PVC if not processed correctly can carry excess lubricants etc into the extrusion which when exuded out behind paint can cause some problems - this is an important quality issue to stay on top of with your extruder -

Many sellers go with strictly cellular PVC so that the paintable surface (using acrylic latex paints) is available on all surfaces - not just the outside, but then they don't have the flexibility of the syntactic polyurethane.

As to what happens in a fire, "safer" product doesn't necessarily sell - I harken back to the early days of the "vertical blind" - the safest ones were made from Polycarbonate - and had to be sand blasted in line to get a uniform finish. They were the cat's meow - nearly indestructible and if burned didn't give you the nasty off all gases mentioned about PVC elsewhere but expensive as all get out. In the end who won out? You guessed it, PVC - no one cleans blinds anymore, they just throw em out and buy new ones to match when it is time to repaint -

good luck

Jim

these are historically done by using an in mold release , then paint in the form of in mold coating , and then structural or rigid foam poured behind.

The in mold coating is is the white you see on commercially avaliable moldings. the apporpriate amount of flame retardant can be added to meet the building specs required

if it is to be used our doors and not painted , it is best to vacuum form pvc skins or films in the mold and then foam behind

let me know if you need a source in the US or China

with best regards

bruce