Fate of methylenediphenyl diisocyanate and toluene diisocyanate in the aquatic environment

Toluene diisocyanate (TDI) and methylenediphenyl diisocyanate (MDI) are hig hly reactive materials used on a large scale in the production of polyureth anes. Their behavior in the aquatic environment has only been reported in g eneral terms. This work provides a clearer understanding of their heterogen eous interaction with water to enable a better prediction of the environmen tal impact of a spill. The kinetics and product distribution have been stud ied for both stirred and unstirred reactions and have been correlated with the degree of agitation, surface area, and stoichiometry. TDI reacts rapidl y, in less than 5 min, when well stirred; and MDI reacts more slowly becaus e of its greater viscosity. However, under poorly mixed conditions,typical of an environmental spill, the reaction of both materials may take several weeks for completion because of the formation of insoluble solid polyurea c rusts. This polyurea is the predominant product under all conditions except at very low loadings of diisocyanate. Under all conditions studied, only l ow concentrations of water-soluble products, including diamines, were forme d. These results are indicative of a reaction occurring predominantly in th e organic phase where the initial hydrolytic product, amine, can react furt her with isocyanate to produce ureas; These studies are consistent with the minimal effects noted from the accidental spillage of TDI and MDI in the e nvironment.