ISO 3001 pdf download.Plastics — Epoxy compounds — Determination of epoxy equivalent
1 Scope
This International Standard specifies a method for the determination of the epoxy equivalent and is applicable to all epoxy compounds. In the case of epoxyamines, it is necessary to apply the modification specified in annex A.
2 Definitions
For the purposes of this International Standard, the following definitions apply. 2.1 epoxy equivalent the mass of resin, in grams, which contains one mole of epoxy groups 2.2 epoxy index the number of moles of epoxy groups contained in 1 kg of resin
3 Principle
The epoxy groups in a test portion are reacted with nascent hydrogen bromide produced by the action of 0,1 mol/l standard volumetric perchloric acid solution on tetraethylammonium bromide. The end-point is determined either using crystal violet as indicator or by a potentiometric method.
4 Reagents
During the analysis, use only reagents of recognized analytical grade. 4.1 Glacial acetic acid. 4.2 Acetic anhydride , purity > 96 %. 4.3 Chloroform. 4.4 Potassium hydrogen phthalate. 4.5 Crystal violet, indicator solution. Dissolve 1 00 mg of crystal violet in 1 00 ml of glacial acetic acid (4.1 ). 4.6 Perchloric acid, 0,1 mol/l standard volumetric solution.4.6.1 Preparation Add 8,5 ml of a 70 % (m/m) aqueous solution of perchloric acid to a solution consisting of a mixture of 500 ml of glacial acetic acid (4.1 ) and 30 ml of acetic anhydride (4.2). Make up to 1 000 ml with glacial acetic acid and mix thoroughly. 4.6.2 Standardization WARNING — The use of safety goggles and a safety screen is recommended. Standardize this solution by titrating it against 200 mg of potassium hydrogen phthalate (4.4) — previously dried, if necessary, for 2 h at 1 20 °C — dissolved in 20 ml of glacial acetic acid (4.1 ) and 1 0 ml of chloroform (4.3), using crystal violet indicator solution (4.5) or a potentiometric titration apparatus (5.1 ). Carry out the end-point determination using 4 to 6 drops of crystal violet solution, titrating until a stable green colour is obtained, or carry out this procedure using a potentiometric titration apparatus. If a potentiometric method is used to determine the epoxy equivalent, it is necessary to use the same method for the standardization of the perchloric acid. Note the temperature t s of the standard volumetric solution.4.7 Tetraethylammonium bromide, reagent solution. Dissolve 1 00 g of tetraethylammonium bromide in 400 ml of glacial acetic acid (4.1 ). Add a few drops of crystal violet solution (4.5). If it changes colour, bring it back to the original (blue-green) colour with standard volumetric perchloric acid solution (4.6). For some epoxy compounds of low reactivity, the use of tetrabutylammonium iodide is advised, either as the solid or as a 1 0 % solution in chloroform. In this case, light shall be excluded as much as possible. Solutions of tetrabutylammonium iodide in chloroform are unstable and shall be freshly prepared for each titration.
5 Apparatus
5.1 Potentiometric titration apparatus, equipped with a silver electrode and a silver chloride or mercury sulfate electrode. 5.2 Balance, accurate to within 0,1 mg. 5.3 Conical flask, capacity 1 00 ml or 200 ml, with ground-glass neck and ground-glass stopper. 5.4 Microburette, with closed reservoir, or calibrated burette, capacity 1 0 ml. 5.5 Glass apparatus, with ground joints, vents being protected from moisture by calcium chloride tubes.5.6 Magnetic stirrer, with polytetrafluoroethylene-coated bar. 5.7 Thermometer, calibrated to permit temperature measurements to within ± 0,1 °C. 5.8 Pipette, capacity 1 0 ml. 5.9 Volumetric flask, capacity 1 000 ml. 5.10 Measuring cylinders, capacity 50 ml and 500 ml.
6 Procedure
6.1 Weigh into the flask, to the nearest 0,1 mg, a test portion containing 0,6 mmol to 0,9 mmol of epoxy groups (this corresponds to a mass of between 0,6 ¥ EE mg and 0,9 ¥ EE mg, where EE is the estimated epoxy equivalent). 6.2 Add 1 0 ml of chloroform (4.3), then dissolve the test portion using the magnetic stirrer (5.6) and, if necessary, by heating slightly. Cool to room temperature, add 20 ml of glacial acetic acid (4.1 ) and then, with the pipette (5.8), 1 0 ml of tetraethylammonium bromide solution (4.7). In the case of high-molecular-mass epoxy resins, increase the chloroform volume to 30 ml. 6.3 If using the indicator method, add 4 to 6 drops of crystal violet solution (4.5) and titrate the solution on the magnetic stirrer with perchloric acid solution (4.6). Carry out the titration until a stable green colour is obtained. 6.4 If using the potentiometric method, place the electrodes in the test solution. Adjust the speed of the magnetic stirrer to give vigourous stirring without splattering. Titrate the solution with perchloric acid solution (4.6). 6.5 Note the temperature t of the perchloric acid solution in order to be able to allow for expansion of the solution with increasing temperature.