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AMERICAN <br /> INDUSTRIAL <br /> HYGIENE <br /> ASSOCIATION <br /> HYGIENIC GUIDE SERIES <br /> Toluene Diisocyanate <br /> (Tolylene Diisocyanate, TDI) <br /> Hg <br /> NCO <br /> Rv' NCO <br /> r (Revised 1967) <br /> Significant Physical Properties <br /> Much of the TDI sold at the present time is an 80-20oo mixture of the 2,4- <br /> and the 2,6-isomers. However, grades rang from IOO fo 2,4-isomer to a 65-357o <br /> mixture of the 2,4- and 2,6-isomers are also available commercially. The literature / <br /> sometimes is not clear as to which TDI isomer or mixture is being discussed, but <br /> the two isomers appear to have similar physiological properties. TDI has many <br /> synonyms and trade names.'' Most grades of TDI initially are colorless liquids <br /> which change to a straw color upon standing and have a powerful acrid odor. In, , <br /> this guide, the specific isomer or mixture of TDI will be mentioned wherever' <br /> possible. <br /> The following data apply for commercial samples of the 2,44somer and an <br /> 80-20% mixture of the 2,4- and 2,6-isomers. <br /> 2,44somer 80-20 Mixture <br /> (Q Molecular weight: 174.16 174.16 <br /> Flash point (COC) : 270oF' 280°F' <br /> Specific gravity of liquid: 1.22 (25°/25°C)' 1.22 (20/20oC)' <br /> Boiling point: 25100 238oC' <br /> Solidification point (maximum) 21°C' 15oC' <br /> Solubility: Both products reactexothermically with <br /> water and are. soluble in aromatic hydro- <br /> carbons, acetone and kerosene. <br /> Odor threshold: 0.4 ppm° <br /> Vapor pressure (80-20 mixture) : mm Hg 0.01' 10' 50' <br /> (approx) <br /> oC 20 122 156 <br /> f At 200C and 760 mm Hg: According to the above vapor pressures. <br /> 1\�i� saturated air would contain approximately <br /> 13 ppm TDI by volume. However, a vapor <br /> pressure value as high as 0.05 mm at 25°C <br /> has been cited' which is equivalent to 65.7 <br /> ppm. The actual ambient air saturation con- <br /> centration most likely lies between these two <br /> extremes. <br /> 1 ppm = 0.00712 mg/liter <br /> I mg/liter = 140.4 ppm <br />