The generation of low concentrations of 2,4-toluenediisocyanate (TDI)

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Abstract
Diisocyanates are used in the polyurethane industry and pose a possible threat to workers exposed to them. A convenient and accurate method for generating low concentrations of 2,4-toluenediisocyanate (TDI) was developed using tetrafluoroethylene Teflon (TFE) permeation tubes. The permeation tubes were prepared by sealing .apprx. 1.5 practical grade TDI in clean spaghetti tubing with solid TFE rod held in place with crimped Al Swagelok ferrules. Tubes of 4.762 mm ID [inner diameter] and 0.762 mm wall thickness and 6.477 mm ID and 0.254 mm wall thickness were sealed with 5.08 and 6.350 mm TFE rods, respectively. Standard ferrules (0.25 in.) were drilled out slightly to accommodate the larger tubing. Using a commercially available air bath capable of maintaining a temperature within 0.05.degree. K, the permeation tubes were kept at 303, 323 and 343.degree. K. TDI was swept from the thermostated chamber with dry N and further diluted with clean dry air to the desired concentrations. The permeation rate was constant when the tubes were maintained at a constant temperature; when the tube experienced a temperature cycle through 343.degree. K, the permeation rate did not return to the original rate. Permeation rates for the thick wall tube were 2.14 ng/min per cm at 303.degree. K, 10.66 at 323.degree. K and 42.84 at 343.degree. K. For the thin wall tube, the permeation rates were 8.30 ng/min per cm at 303.degree. K, 45.39 at 323.degree. K and 179.62 at 343.degree. K. The tubes were expected to have a lifetime of at least 1 yr.
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