1、 Standard Method of Test for Analysis of Structural Steel Coatings for Isocyanate Content AASHTO Designation: T 339-10 (2015)1 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-4c T 339-1 AASHTO Standard Method of Te
2、st for Analysis of Structural Steel Coatings for Isocyanate Content AASHTO Designation: T 339-10 (2015)11. SCOPE 1.1. This method is designed for the determination of the isocyanate (NCO) content of the resin system found in polyurethane paints. 1.2. The values stated in SI units are to be regarded
3、as the standard. 1.3. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior t
4、o use. 2. APPARATUS AND MATERIALS 2.1. Analytical balance. 2.2. High-speed centrifuge. 2.3. Centrifuge tubes, minimum 50-mL heavy-wall glass with vinyl-lined screw caps or 50-mL high-speed 9400 relative centrifugal force (RCF) polypropylene tubes with screw caps. 2.4. 10-mL syringes with Luer slip t
5、ip and caps. 2.5. Automatic titrator with stirrer (Mettler-Toledo DL 50 or equivalent). 2.6. pH electrodes. 2.7. Fleaker or other vessel with stopper or cap, 200-mL minimum volume. 2.8. o-xylene, reagent grade, dried over 3A molecular sieve (see Section 4.1). 2.9. Standard buffer solutions, pH 4.00
6、and pH 7.00. 2.10. Dibutylamine, 99 percent assay. 2.11. Methanol, ACS reagent grade, dried over 3A molecular sieve (see Section 4.1). 2.12. Hydrochloric acid solution, 1.0 N. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violati
7、on of applicable law.TS-4c T 339-2 AASHTO 3. PROCEDURE 3.1. To analyze a one-component material, the resin system must first be separated from the whole paint. 3.2. Place a 45-mL sample of the whole paint into a high-speed centrifuge tube and cap immediately. 3.3. Centrifuge the sample to produce a
8、minimum RCF of 4300 until the pigment and resin have separated. See Section 5.1 for RCF equation. 3.4. No separation is required for multi-component materials when the resin system is packaged separately. The resin system is generally labeled “curing agent” or “part B.” 3.5. Calibrate the titrimeter
9、 and pH electrodes with standard buffer pH 7.00 and pH 4.00 solutions. 3.6. Place 25 mL of dried o-xylene into an appropriately sized vessel. 3.7. Weigh a 10.0-g sample of resin solution from materials having an expected isocyanate value of less than 15.0 percent or 4.0-g sample of resin solution fr
10、om materials having an expected isocyanate value of 15.0 percent or greater into the vessel from Section 3.6. 3.8. Record the sample weight to the nearest 1.0 mg. 3.9. Add 20.00 mL of 1.7 N dibutylamine solution to the vessel from Section 3.6. The 1.7 N dibutylamine solution is prepared by diluting
11、290 mL of dibutylamine to 1.0 L with dried o-xylene. 3.10. Cap the vessel immediately. 3.11. Allow the sample to stir for a minimum of 15 min but no longer than 60 min at 25 2C. 3.12. Prepare a blank in the same manner, omitting the resin solution. 3.13. Wash down the sides of each vessel with 100 m
12、L of dried methanol. 3.14. Titrate the stirred blank with 1.0 N hydrochloric acid to the end point, which occurs at pH 5.0. 3.15. Record the volume of titrant used to the nearest 0.01 mL. 3.16. Titrate the stirred sample with 1.0 N hydrochloric acid to the end point, which occurs at pH 5.0. 3.17. Re
13、cord the volume of titrant used to the nearest 0.01 mL. 3.18. Prepare and titrate a duplicate sample. 3.19. Calculate the weight percent isocyanate. Duplicate analyses should not differ by more than 0.1 weight percent. See Section 5.2 for weight percent isocyanate calculation. 2015 by the American A
14、ssociation of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4c T 339-3 AASHTO 4. NOTES 4.1. Methanol and o-xylene used for this titration should be passed through separate columns containing 3A molecular sieve to remove any moisture t
15、hat may be present. A recommended flow rate for passing methanol or o-xylene through a drying column is approximately 100 mL/min. Dried stock may be collected into amber bottles and preserved by placing a small amount of 3A molecular sieve in the bottles. 5. CALCULATIONS 5.1. Calculation for Relativ
16、e Centrifugal Force (RCF): RCF = 0.00001118 r N2(1) where: RCF = Relative Centrifugal Force, r = rotating radius (cm), and N = revolutions per minute. 5.2. Calculation of weight percent isocyanate of the sample: %NCO = (BS) N 42)/(1000 W) 100 (2) where: B = the amount of titrant used to titrate the
17、blank in milliliters, S = the amount of titrant used to titrate the sample in milliliters, N = the normality of the hydrochloric acid solution in equivalents per liter, 42 = the equivalent weight of an isocyanate group, 1000 = the factor converting liters to milliliters, and W = the weight of the re
18、sin solution sample in grams. 6. REPORT 6.1. Report the resin solution sample weight to the nearest milligram, 0.001 g. 6.2. Report the percent isocyanate of the resin system in duplicate to the nearest 0.1 percent. 1Formerly AASHTO Provisional Standard TP 67. First published as a full standard in 2009. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.
