1、 FORD LABORATORY TEST METHOD AI 103-01 Date Action Revisions 2000 08 07 Editorial no technical change A. Cockman 2000 03 09 Editorial no technical change A. Cockman 1993 12 31 Printed copies are uncontrolled Page 1 of 6 Copyright 2000, Ford Global Technologies, Inc. IODOMETRIC DETERMINATION OF HYDRO
2、PEROXIDES IN CLEARCOAT ENAMELS Application This test method determines the amount of hydroperoxides in automotive clearcoat enamels. Hydroperoxide is produced during weathering of clearcoats and can be monitored as a func tion of exposure time in a weatherometer. This information provides a way to e
3、valuate the durability of coatings based on chemical changes and should be used only as a comparison tool for modifications within a coating family (acrylic melamine coatings, f or example). Required Test Equipment Silicone oil bath and heat source Ice bath Condenser - with 24/40 ground glass joints
4、 Erlenmeyer flask - 125 Ml, with 24/40 ground glass joint Freezer mill Solvent repurification apparatus Kontes catalog # 5476 00 - 0500 Titroprocessor System - with the following elements* Brinkmann 670 Titroprocessor or equivalent Titration stand and titration vessel Dosimat and exchange unit Polar
5、izer Double platinum electrode Necessary cables and accessories * or similar equi valent Computer Software Required Titroprocessor method for “Hydroperoxide Determination“* Titroprocessor method for “Thiosulfate Standardization“* *Source Ford Central Laboratory Services FORD LABORATORY TEST METHOD A
6、I 103-01 Page 2 of 6 Copyright 2000, Ford Global Technologies, Inc. Materials and Solutions Required Methylene Chloride Potassium Iodide, Iodate-free Sodium Thiosulfate Pentahydrate Sodium Carbonate Potassium Dichromate Glacial Acetic Acid Calcium Hydride 2-Propanol, Hydroperoxide-free Acetic acid/2
7、-propanol solution - 1:9 by volume Sodium Thiosulfate - 0.00500 M Conditioning and Test Conditions All test values indicated herein are based on material conditioned in a controlled atmosphere of 23 +/ - 2 C and 50 +/ - 5 % relative humidity for not less than 24 h prior to testing and tested under t
8、he same conditions unles s otherwise specified. Preparation of Panels 1. To allow for 10 data points of hydroperoxide content versus hours of weathering, spray up five 125 x 175 mm glass panels for each type of enamel using FLTM BI 103 - 02. Panels must have 1.0 - 1.4 g of clear coat solids. 2. Cure
9、 the panels at the time and temperature recommended by the relevant engineering document. 3. Wrap the panels in foil, seal them in plastic bags, and age for 72 h at 23 +/ - 2 C. 4. Perform a hydroperoxide determination on a sample of unweathered coating to provide a “time zero“ baseline. 5. Place th
10、e panels in a weatherometer according to SAE J1960 and remove for hydroperoxide determinations at the time intervals suggested by the ongoing determinations. If the values are changing rapidly with weathering, per form hydroperoxide determinations frequently. If the values appear to be stable, remov
11、e panels for testing less often. See Note 1. Procedure 1. Turn on the magnetic stirrer/hot plate to warm the silicone oil bath to 110 +/ - 5 C. 2. Turn on water to the co ndenser at a fast flow rate to provide adequate cooling for the refluxing solvent. FORD LABORATORY TEST METHOD AI 103-01 Page 3 o
12、f 6 Copyright 2000, Ford Global Technologies, Inc. 3. Turn on the titroprocessor, stir plate, and dosimat, in that order, to warm the electronics. 4. Using a clean razor blade, scrape approximately half of the clearcoat soli ds from a 125 x 175 mm glass panel. Return the glass panel to the weatherom
13、eter so that the remainder of the clearcoat solids can be analyzed at a later date. 5. Transfer the scraped, flake - like material to a cryogrinding tube, insert an impactor, and seal up the tube. 6. Insert the cryogrinding tube in a freezer mill and pour liquid nitrogen into the mill up to the fill
14、 line. Cryogrind the polymer for 5 minutes. 7. Remove the cryogrinding tube from the freezer mill. Warm the tube to 23 +/ - 2 C before open ing it to prevent the condensation of moisture on the cryogrind powder. 8. Open the cyrogrind tube and examine the contents. A dust - like powder is desired. If
15、 pieces, flakes or chunks are visible, further grinding is required. See Note 2. 9. Transfer the powder from the cyrogrind tube to a brown glass jar labeled with sample identification. Using an analytical balance, weigh 0.5 g of the cyrogrind powder to 0.0001 g on tared wax weighing paper. Place the
16、 weighed powder in a 125 mL Erlenmeye r flask with a 24/40 ground glass joint. 10. Add 10 mL of methylene chloride, stopper the flask, and swirl to wet the powder. Allow the mixture to stand for 10 minutes to swell the powder. 11. Place a magnetic stir bar and a few pieces of dry ice in the Erlenmey
17、er flask. Add 0.3 g of potassium iodide followed by 25 mL of acetic acid/isopropyl alcohol solution. Swirl the flask to ensure mixing, attach the flask to the water condenser and immerse the flask in the pre - heated oil bath. Carefully place a stopper in the top of the condenser to prevent the entr
18、y of oxygen and loss of solvent. 12. Reflux gently for at least 15 minutes. If hydroperoxide is present, a yellow color will develop during reflux. S ee Note 3. 13 . After completion of the reflux, remove the flask and condenser from the oil bath. Remove the stopper from the top of the condenser and
19、 place a piece of dry ice on the top of the condens er. 14. Place the flask and condenser in an ice bath and cool the flask to 23 +/ - 2 C. 15. From the titroprocessor, access the method called “Hydroperoxide Determination“. Go to page 8 of the method. Edit line 3 and enter sample identification. Ed
20、it line 9 and enter for SO the sample weight of the cyrogrind powder (from Step 9). 16. Transfer the cooled reaction mixture to the titration vessel, using small portions of additional acetic acid/isopropyl alcohol solution to rins e all yellow particles into the titration vessel. A small stir bar (
21、one that will not hit the electrode) must be in place in the titration vessel. 17. Clamp the titration vessel in place and make sure the mixture is stirring smoothly. From page 8, hit the START button on the titroprocessor. 18. Titrate with 0.00500 M Na 2 S 2 O 3 beyond the disappearance of the yell
22、ow color. Also observe the display of the real - time titration curve. The mV readings will reverse direction after the endpoint has been passed. Hit t he BREAK key on the titroprocessor to terminate the run. The titroprocessor will calculate the hydroperoxide content (R1) in “mol of hydroperoxide/g
23、 of clearcoat solids“. FORD LABORATORY TEST METHOD AI 103-01 Page 4 of 6 Copyright 2000, Ford Global Technologies, Inc. Cleanup Procedure 1. After pouring the titration mixture into a solvent waste container, rinse the titration vessel with methylene chloride and wipe out the remaining solids before
24、 performing the next run. Between each run, rinse the electrode with methylene chloride and th en with water. 2. Wash cyrogrind tubes with soapy water, scrubbing surfaces with a stiff brush to completely remove adhered powder. Rinse only with distilled water. Preparation of Solutions Acetic Acid/2-p
25、ropanol Place approximately 25 g of calcium hydride in the bottom of a 2000 mL, 2 - neck round bottom flask. Add approximately 1 L of isopropyl alcohol. Attach the flask to the solvent repurification apparatus. Close the Teflon stopcock next to the solvent drainoff and open the other stopcock. Reflu
26、x for several hours. Close the stopcock and collect approximately 50 mL of alcohol in the upper part of the solvent repurification system. Open the solvent drain stopcock and drain off the 50 mL of solvent and discard it. Collect and then drain approximately 450 mL of alcohol into a 1 - L graduated
27、cylinder. Add 50 mL of acetic acid. Transfer the solution to a brown bottle. Through the side arm, add additional 2 - propanol and repeat the process until the desired amount of solu tion has been prepared. Before using a freshly - prepared batch of acetic acid/2 - propanol, perform a hydroperoxide
28、determination on a “blank“. No hydroperoxide should be present in the titration solution. Sodium Thiosulfate, 0.005 M Prepare the sodium thiosu lfate by dissolving 1.25 g of Na 2 S 2 O 3 5H 2 O in 1 L of freshly boiled, cooled distilled water. Add a small amount (less than 0.1 g) of sodium carbonate
29、 to the solution. Store the solution in a brown glass dosimat bottle and allow it to stand for 24 h. Flush the new sodium thiosulfate solution through the lines of the titrating system before standardizing the solution. Potassium Dichromate Solution Dry a portion of K 2 Cr 2 O 7 at 104 C for 3 h. We
30、 igh 0.25 g of K 2 Cr 2 O 7 to 0.0001 g, quantitatively transfer it to a 1000 mL volumetric flask and dilute to volume with distilled water. Calculate the molar concentration of the potassium dichromate solution. (FW of K 2 Cr 2 O 7 = 294.19) Protect the solution from light. Standardization of 0.005
31、 M Sodium Thiosulfate with Potassium Dichromate Access the method in the titroprocessor called “thiosulfate standardization“. Enter the molar concentration of the potassium dichromate solution on p 7 of the method (va riable C2). On p 3, change TBEG, VOLUME so that it represents 85 - 90 % of the exp
32、ected titration. Pipette 10.00 mL of standard potassium dichromate solution into a 125 mL Erlenmeyer flask with 24/40 ground glass joint. Add 0.1 g of iodate - free potassium i odide and a small piece of dry ice to the flask. Then add 10 drops of concentrated hydrochloric acid and stopper the flask
33、for 10 minutes. Transfer the mixture to a titration vessel using 20 mL of distilled water. Titrate the liberated iodine with sodium thiosulfate. The titroprocessor will calculate the sodium thiosulfate concentration (R1). Perform at least 3 determinations. Enter the average sodium thiosulfate concen
34、tration in the titroprocessor method called “hydroperoxide determination“ on p 7 (variable C1 in mol/L). FORD LABORATORY TEST METHOD AI 103-01 Page 5 of 6 Copyright 2000, Ford Global Technologies, Inc. Chemicals, materials, parts, and equipment referenced in this document must be used and handled pr
35、operly. Each party is responsible for determining proper use and handling in its fa cilities. General Information Notes: 1. Hydroperoxide is unstable. Therefore, the hydroperoxide content of a clearcoat enamel should be determined immediately after its removal from the weatherometer. If it is not po
36、ssible to do so, the coating must be pro tected from light. Glass panels can be wrapped in foil and sealed in plastic bags. Coatings can be scraped from the panels and cyroground. The powder can then be stored in brown glass jars. Refrigeration of the clearcoat until the time of analysis is recom me
37、nded. 2. Crosslinked polymers like clearcoat enamels are not soluble in the acetic acid/isopropyl alcohol titration solvent. Lack of solubility means the I must diffuse into the polymer to reduce covalently bound hydroperoxides to alcohols and the resul ting I 3 - must diffuse out to react with thio
38、sulfate. Diffusion is facilitated by cryogrinding the polymer to a fine powder and then swelling the powder with methylene chloride. The presence of residual yellow color on the polymer powder after the titration with thiosulfate indicates that diffusion is not occurring sufficiently fast to ensure
39、complete reaction. Grinding the powder to an even smaller particle size shou ld remedy this problem. 3. The complete reduction of hydroperoxid e by I - in the reflux reaction can be verified by increasing the reflux time. For each unstudied coating family, i t is recommended that the hydroperoxide d
40、etermination on a given sample be r epeated with the reflux time extended from 15 min to 1 hour. If the value for the hydroperoxide content is the same after the 1 hour reflux, 15 minutes is adequate for complete reaction. Iodometric Determination of Hydroperoxide in Clearcoat Enamels 1. In Step 12
41、of the Procedure, hydroperoxide is reduced to alcohol by iodide in the presence of acid: YOOH + 3 I - + 2 H + YOH + H 2 O + I 3 - One mol of YOOH generates 1 mol of I 3 - - . 2. In Step 18 of the Procedure, tri - iodide ion is reduced to iodide by thiosulfate: 2 S 2 O 3 - 2 + I 3 - S 4 O 6 2 + 3 I -
42、 Two mols of S 2 O 3 - 2 are required to reduce 1 mol of I 3 - . 3. The amount of hydroperoxide in the clearcoat, expressed as mol YOOH/g clearcoat solids, is calculated as follows: mol YOOH/g clearcoat solids = mL of Na 2 S 2 O 3 x Na 2 S 2 O 3 (mol/L) x mol YOOH/2 mol Na 2 S 2 O 3 x L/1000 mL / Wt
43、 of clearcoat solids (g) FORD LABORATORY TEST METHOD AI 103-01 Page 6 of 6 Copyright 2000, Ford Global Technologies, Inc. Standardization of Sodium Thiosulfate with Potassium Dichromate 1. Dichromate oxides iodide in the presence of acid to iodine. Cr 2 O 7 2 + 6 I - + 14 H + 2 Cr +3 + 3 I 2 + 7 H 2
44、 O 2. The liberated iodine is reduced back to iodide by thiosulfate. 2 S 2 O 3 - 2 + I 2 S 4 O 6 2 + 2 I - 3. Overall reaction: Cr 2 O 7 2 + 6 S 2 O 3 2 + 14 H + 2 Cr +3 + 3 S 4 O 6 2 + 7 H 2 O 4. The concentration of the sodium thiosulfate solution is calculated as follows: Na 2 S 2 O 3 (mol/L) = mL of K 2 Cr 2 O 7 x K 2 Cr 2 O 7 (mol/L) x 6 mol Na 2 S 2 O 3 /mol K 2 Cr 2 O 7 / mL of Na 2 S 2 O 3
