Effects of diisocyanate

A study by Thome et al. (1987) described the effects of diisocyanates after topical exposure. The dermal sensitization capabilities HDI and several other isocyanates (TDI, MDI, HDI) in BALB/cBy mice exposed to a variety of topical doses of each isocyanate was performed. Groups of 4-32 male mice were exposed to dermal doses of HDI in acetone. A topical dose of HDI at 2,800 mg/kg was shown to be lethal to 100% of the mice within 16 horns of exposure. No other reports of death after topical exposure to HDI were located. 

Fig. 3.1. Effect of diisocyanate on torsional modulus of polyester urethanes. NDI= 1,5-naphthalene diisocyanate TOD = 3,3 -toluene-4,4-diisocyanate DMDI= 3,3 -dimethyl-4,4 -diphenylmethane diisocyanate MDI= 4,4 -di-phenylmethane diisocyanate.

EFFECT OF DIISOCYANATE STRUCTURE ON THE RELATIVE THERMAL STABILITY OF POLYURETHANE ELASTOMERS... 

Skin irritation can also be caused by amine accelerators, e.g., MDA (van Joost et al. 1987), triethylene-diamine (Adams 1983) and triethylamine (Malten 1964). Concentrated liquids may even be corrosive. The irritant effect of diisocyanates in the hardeners, glues and paints may also be attributed to the solvents used in these products. Completely hardened PU products usually do not cause skin problems. However, some unreacted isocyanate monomer may remain in surplus inside the PU foam, even after curing. During machining and cutting, PU dust containing isocyanate is produced. When heated to above 250 °C, PU polymers decompose into isocyanates and nitrogen oxides, and may then cause dermatitis (Bjorkner 1992). 

The reaction rates of diisocyanates are strongly influenced by their molecular structure. The reactivity of isocyanate groups is enhanced by adjacent electron-withdrawing substituents. Aromatic rings are very effective electron withdrawing groups, and it is for this reason that the majority of commercial diisocyanates are aromatic. Many of the diisocyanates used commercially consist of mixtures of isomers. Some of the more important commercial diisocyanates are illustrated in Fig. 25.6. Diisocyanates must be handled carefully to avoid exposing workers to their hazardous vapors. 

Polymer Matrix Effects. In order to approximate the environment experienced by the arylcarbamate moieties in coatings based on aromatic diisocyanates, we chose to study the photochemistry of alkyl N-arylcarbamates in polymethacrylate (PMMA) and polypropyl-methacrylate (PPMA) films. First, however, 2a and 3a were irradiated in ethyl propionate (a model solvent for PMMA and PPMA) to determine the effect of the solvent polarity (dielectric) on the photolysis of the carbamates. Upon excitation at 280 nm, where the solvent absorbance was negligible, is 0.006 for 2a and 0j) is 0.005 for 3a. These values are significantly smaller... 

In this contribution, we report equilibrium modulus and sol fraction measurements on diepoxidet-monoepoxide-diamine networks and polyoxypropylene triol-diisocyanate networks and a comparison with calculated values. A practically zero (epoxides) or low (polyurethanes) Mooney-Rivlin constant C and a low and accounted for wastage of bonds in elastically inactive cycles are the advantages of the systems. Plots of reduced modulus against the gel fraction have been used, because they have been found to minimize the effect of EIC, incompleteness of the reaction, or possible errors in analytical characteristics (16-20). A full account of the work on epoxy and polyurethane networks including the statistical derivation of various structural parameters will be published separately elsewhere. 

Tarlo, S.M., Liss, G.M., and Yeung, K.S., Changes in rates and severity of compensation claims for asthma due to diisocyanates a possible effect of medical surveillance measures, Occup. Environ. Med., 59, 58, 2002. 

The effects of chemical structure of diisocyanate component on the hydrolysis of polyurethanes by R. delemar lipase were examined (Figure 8). The rates of hydrolysis of the polyurethanes containing MDI or tolylene-2,U-diisocyanate (TDI) were smaller than that of the polyurethane containing 1,6-hexamethylene-diisocyanate (HDI). 

Figure 8. Effects of chemical structure of diisocyanate component on the hydrolysis of polyurethanes by R. delemar lipase.

Diluent added during crosslinking has two main effects it Increases the population of elastically Inactive cycles and it weakens the interchain constraints. Studies of poly(oxypropylene) triol-diisocyanate networks in the presence of diluent have shown that the effect of diluent on the equilibrium modulus is much stronger than would correspond to the effect of cycles (Figure 10) (32) which again corroborates the concept of permanent interchain constraints. 

In order to avoid the use of lead compounds on environmental grounds, lithium fluoride (liF) has been chosen to obtain super-rate burning of nitramine composite propellants.P7281 Typical chemical compositions of HMX composite propellants-with and without liF are shown in Table 7.4. The non-catalyzed HMX propellant is used as a reference pyrolant to evaluate the effect of super-rate burning. The HMX particles are of finely divided, crystalline (3-HMX with a bimodal size distribution. Hydroxy-terminated polyether (HTPE) is used as a binder, the OH groups of which are cured with isophorone diisocyanate. The chemical properties of the HTPE binder are summarized in Table 7.5. 

We have already been introduced to polyurethane chemistry in Chapter 10, Section 2, where we used toluene diisocyanate (TDI) reacting with a diol to give a polyurethane. Polyurethanes derived from MDI are more rigid than those from TDI. New applications for these rigid foams are in home insulation and exterior autobody parts. The intermediate MDA is now on the Reasonably Anticipated to Be Human Carcinogens list and the effect of this action on the market for MDI remains to be seen. The TLV-TWA values for MDA and MDI are some of the lowest of the chemicals we have discussed, being 0.1 and 0.005 ppm respectively. 

Existing Information on Health Effects of Hexamethylene Diisocyanate... 

This public health statement tells you about hexamethylene diisocyanate (HDI) and the effects of exposure. 

In addition to their local irritant effects on the respiratory tract, the diisocyanates also have a propensity to induce an immimological response in some individuals, which is characterized by an asthma-like respiratory reaction, and will induce the formation of antibodies to both the monomeric and polymer forms of HDl. A few studies have examined the immimological effects of HDl toxicity in humans, with some data available from laboratory animal studies as well. 

This section will describe clinical practice and researeh concerning methods for redueing toxic effects of exposure to hexamethylene diisocyanate. However, because some of the treatments discussed may be experimental and unproven, this section should not be used as a guide for treatment of exposures to hexamethylene diisocyanate. When specific exposures have oceurred, poison eontrol centers and medical toxicologists should be consulted for medieal advice. The following texts provide specific information about treatment following exposures to hexamethylene diisocyanate ... 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the Administrator of EPA and agencies and programs of the Public Health Service) to assess whether adequate information on the health effeets of hexamethylene diisocyanate is available. Where adequate information is not available, ATSDR, in eonjunction with the National Toxicology Program (NTP), is required to assure the initiation of a program of research designed to determine the health effects (and techniques for developing methods to determine such health effects) of hexamethylene diisocyanate. 

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals to hexamethylene diisocyanate are summarized in Figure 2-4. The purpose of this figure is to illustrate the... 

Ferguson JS, Schaper M, Alarie Y. 1987. Pulmonary Effects of a Polyisocyanate Aerosol Hexamethylene Diisocyanate Trimer (HDlt) or Desmodur-N (DES-N). Toxicol Appl Pharmacol 89(3) 332-346. 

Huang J, Wang XP, Chen BM, et al. 1991a. Immunological effects of toluene diisocyanate exposure on painters. Arch Environ Contam Toxicol 21(4) 607-611. 

Karol MH, Hansen GA, Brown WE. 1984. Effects of inhaled hexamethylene diisocyanate (HDI) on guinea pig cholinesterases. Fimd Appl Toxicol 4(2 Pt l) 284-287. 

Kazuyuki 0, Higashi T, Nakadate T, et al. 1992. Fom year follow-up of effects toluene diisocyanate exposure on the respiratory system in polyurethane foam manufacturing worker. Int Arch Occup Environ Health 63 565-569. 

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