Methylene diisocyanate , health

PMDA, 20 266. See also Polymeric methylenedianiline (PMDA) PMDA-ODA, gel casting of, 20 271-272 PMDA-ODA structures, 10 214 PMDI polymeric isocyanate, 25 456, 457, 462. See also Polymeric methylene diisocyanate resins (PMDI) rigid polyurethanes from, 25 471-472 PMF/PMUF resins, 15 779 PMF resins, hardening of, 15 781 PMMA ionomer, 4DA and, 14 479 PM optimization (PMO), 15 466 PM process, 21 50 Pneumatic classification, 22 288 health and safety factors related to,... 

PU are compounds formed by reacting the polyol component with an isocyanate compound, typically toluene diisocyanate (TDI) methylene diisocyanate (MDI) or hexamethylene diisocyanate. Polyols are relatively non-toxic (i.e., polyether type polyols are found to be safe, because they are low in oral toxicity with almost no irritation effect to the eyes and skin), however, isocyanates are highly toxic and the product can have a significant toxicity if remnants of isocyanate are in it, which manifests itself mainly as a respiratory (as well as a dermal) hazard. Exposure to the vapour of isocyanates directly may cause irritation for the eyes, respiratory tract and skin. Such an irritation may be too severe to produce bronchitis and pulmonary oedema. As health hazards of isocyanates are considered, one immediately remembers one of the worst industrial disasters of the 20th century, that occurred in Bhopal, India, because of the toxic cloud of methyl isocyanate was released accidentally from the Union Carbide pesticide factory in December 1984. An estimated 3,000 people died immediately with a final of some 20,000, most suffocating from the cloud s toxic chemicals, and some 50,000 were injured, most were residents living near the plant. 

CAUTION The handling of isocyanates should be done with great care because of their known toxicity hazard. The hazards and chemistry of methyl isocyanate have recently been reported. Toluene diisocyanate (TDI), methylene diisocyanate (MDI), and methyl isocyanate (MIC) are flammable, very reactive, and have in common low maximum allowable concentrations for employee exposure by the Occupational Safety and Health Administration (OSHA). 

Important commercial isocyanates include the diisocyanate monomers toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and MDI-, TDI-, and HDI-based isocyanates (e.g., prepolymers and polyisocyanates). World-wide production volume is estimated at over 12 billion lb. Isocyanates (diisocyanates, polyisocyanates, and prepolymers) all cause similar health effects, most commonly asthma [32]. Isocyanates are reported to be the leading attributable cause of work-related asthma [16]. Isocyanates are potent sensitizers that can trigger a severe and potentially fatal asthma attack in sensitized persons at very low isocyanate exposure levels [16]. Toluene diisocyanate is reasonably anticipated to be a human carcinogen by National Toxicology Program. 

Isoouanates. Various isocyanates are employed in the polymer industry. These compounds are powerful irritants and they are highly toxic. Of particular interest are methylene-di-paraphenylene isocyanate (MDI) and toluene-2,4-diisocyanate (TDI). Various alkyl isocyanates (e.g., methyl, ethyl, propyl, butyl, and cyclohexyl) derivatives may also be of current interest with respect to potential occupational health hazards. Simultaneous analysis of MDI and TDI by HPLC has been accomplished by a modification of the method of Dunlap et al. (28). Air samples are collected in impingers containing p-nitrobenzyl-n-... 

Toxicity. While many new materials are added to the adhesive chemist s arsenal, some are being removed as well. Compounds which cause health and environmental concern include ethylenimine, methylene-fcw(o-chloroan-iline) (MOCA), hexamethylene diisocyanate, formaldehyde. Some systems are no longer in use in others, modifications have been made. Thus radiation-curing technology is replacing some types of multifunctional acrylate monomers with alkoxylated compounds, because the latter are less irritating and less toxic. An example is trimethylolpropane triethoxy triacrylate. 

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