Hexamethylene diisocyanate hazards

Morel CM, Gendre M, Cavigneax A, et al. 1981. 1,6-hexamethylene diisocyanate. Hazard Summary. Cahiers de Notes Documentaires 105 633-636. 

The Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in the nation. These sites make up the National Priorities List (NPL) and are the sites targeted for long-term federal clean-up activities. Hexamethylene diisocyanate has not been found in any of the 1,445 current or former NPL sites. However, the total number of NPL sites evaluated is not known. As more sites are evaluated, the number of sites at which HDI is found may increase. This is important because exposure to this substance may harm you and because these sites may be sources of exposure. 

Union Carbide also patented a phosgene-free process for making hexamethylene diisocyanates [40] (Scheme5.5). In this later process, 1,6-hexanediamine was reacted with dry-ice, trimethylchlorosilane, and trichlorophenylsilane to form a halosilyl carbamate intermediate and then converted to the corresponding diisocyanate. However, it should be noted that trichlorophenylsilane used in this process is on the EPA s Extremely Hazardous Chemicals List (40 CFR Part 355, Appendix A). 

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. 

Hazardous Decomp. Prods. Heated to decomp, emits CO, CO2, NOx, hydrogen cyanide, hexamethylene diisocyanate Storage Darkens on exposure to sunlight Uses In surface coating systems such as urethane (polyurethane) paints and varnishes... 

The principal aliphatic isocyanates used are 1,6-hexamethylene diisocyanate (HDD (1,6-isocyanatohexane) [822-06-0], bis(4-isocyanatocyclohexyl)methane (H12MDI) [5124-30-1], and isophorone diisocyanate (IPDI) (3-isocyanato-l-iso-cyanatomethyl)-l,3,3-trimethylcyclohexane [4098-71-9]. Tetramethyl-m-xylidene diisocyanate (TMXDI) [2778-42-9] and m-isopropenyl-a,a-dimethylbenzyl-isocyanate (TMI) (l-(l-isocyanato-l-methylethyl)-3-(l-methylethenyl)benzene [2094-99-7] are specialty products used on a much smaller scale. Diisocyanates are only used as higher molecular weight derivatives in coatings to increase functionality and reduce toxic hazard. 

Moisture-curing systems are based on isocyanate-terminated branched prepolymers which cure by interaction with atmospheric moisture. The prepolymers are prepared by reaction of an excess of diisocyanate (e.g. tolylene diisocyanate, diphenylmethane diisocyanate or hexamethylene diisocyanate) with polyol (polyester, polyether or castor oil). It is important that the residual free diisocyanate content should be low to reduce toxic vapour hazards. When the pre-polymer is exposed to moisture, the following reactions occur and cure is effected ... 

Hexamethylene-1,6-diisocyanate is listed as a hazardous air pollutant (HAP) imder to Section 112 (b) of the Clean Air Act (CAA) (U.S. Congress 1990). The national emission standards for hazardous air pollutants (NESHAP) which were established pursuant to Section 112 of the CAA (as amended November 15, 1990), regulate specific categories of stationary sources that emit or have the potential to emit one or more HAPs. HDl is listed as a volatile HAP for wood furniture manufacturing operations in Title 40 of the Code of Federal Regulations (CFR), Part 63, Subpart JJ (EPA 1995). 

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