Comparison of Physical Hazards Between Two Plastic Foams -Polyurethane, Polystyrene-

Both Polyurethane and polystyrene foams are light and good thermal insulators, and therefore widely used in individual homes and general buildings. However, nonflammable CFC chemicals were replaced by alternative foaming agents, due to their global warming potential. Since foamed polymers themselves are combustible, it is necessary to contain sufficient amount of retardant. In these 2 polymer foams, formerly brominated fire retardants were used, but now they are not available due to the prohibition by the framework of Stockholm Convention on Persistent Organic Pollutants (POPs) .

In order to produce the polyurethane foam, carbon dioxide and/or HFC gas, etc., are put in as foaming agent, and regarding fire retardant, phosphorus compounds are usually used, where PBB (Polybrominated biphenyls) was replaced due to above mentioned framework. In the polystyrene foam production, butane gases were introduced as foaming agent, and at present, retardant candidate situation for replacing HBCD is in a transition period.

On September 24, U.S. EPA released draft report for public comments, titled “Flame Retardant Alternatives for Hexabromocyclododecane (HBCD). Hereupon, only two kinds of brominated polymer retardant candidates for polystyrene foams (XPS, EPS) were listed; 1) Butadiene styrene brominated copolymer (CAS RN 1195978-93-8), 2) Tetrabromobisphenol A-bis brominated ether derivative (CAS RN 97416-84-7) . 

In general, these polymer retardants have lower toxicity, though persistent organic pollutants. It is  said that polymer is not so easy to be introduced to the living organisms, so its toxicity is rather low. Since, at present, their decomposed products and also the existing products in recycle stages are not so precisely studied, yet, the study for the released products, heated at higher temperature, will be very necessary.

This manuscript describes the physical hazard comparison for 2 kinds of plastic foams: rigid polyurethane foam and polystyrene foam (XPS), used for insulator, at the temperature of nearly 100C and 400C.

In the concrete, to compare the evolving gases caused by heated and/or decomposed plastic foams, which also contain different retardant and foaming gas, the “easy handling heating device for gas extraction” was assembled. The evolving gases were analysed by mainly gas chromatography (TCD, FID) and FT/IR, with partially assisted by Py/GC-MASS and TG MASS.

As for “easy handling heating devise for gas extraction”, 100mg plastic foam, placed in an inner glass tube cell (4ml) at the neck part of metal vessel (diameter: 63.5mm), was heated at ceramic oven with temperature controlling device. At the top of the neck part, SWEGELOCK jig was attached with silicone cap, in order to catch gas by microsyringe.

In the result, the extruded polystyrene foam (“Styrofoam 1B”, by Dow Kakoh K.K.) released flammable butane gases (iso-butane, n-butane) at nearly 100C, while no such kinds of gases were detected by rigid polyurethane foam (“EMOB”, by Softpren Industry Corp.). At higher temperature of nearly 180C, HFC gas was found.  

On the other hand, regarding the toxic gases at much more higher temperature of nearly 400C, released from above mentioned extruded polystyrene foam (XPS), gas chromatograph mainly showed CO peak, while CO, HCN and isocyanate products from rigid polyurethane foam.