Flexible polyurethane foam made from diphenylmethane-4,4'-diisocyanate (MDI) may contain a few ppm of residual monomer. As this foam is used in consumer articles like upholstered furniture and bed mattresses, the question arises if the residual monomer can result in consumer exposure and risk to consumer health. Integral skin polyurethane foam used for steering wheels and armrests and flexible polyurethane foam were analyzed for extractable MDI. The latter was also investigated with respect to migration and evaporation of MDI. There was no migration or evaporation of MDI detected. Against the experimental design and the corresponding detection limits less than 5.4 ng MDI per m(3) air in the test chamber and a migration rate below 9 ng/cm(2) per day was found under simulated worst-case conditions (up to 10 ppm MDI in the flexible foam). For exposure by inhalation, these findings were compared to the German MAK value for MDI in air, the US EPA Reference Concentration and the NOAEC for respiratory tract irritation. For dermal exposure, the findings were compared against a derived No Expected Sensitization Induction Level (NESIL) for allergic contact dermatitis in man. As a result, polyurethanes containing up to 24 ppm extractable MDI do not pose a critical toxicological risk to consumers. Whether higher contents are acceptable depends on the result of migration and evaporation tests.
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