Different determination methods of epoxy equivalent and epoxy value

Epoxy equivalent and epoxy value (epoxy equivalent = 100 / epoxy value), the main determination methods are based on the energy of hydrogen halide, thiosulfate (ester) and mercaptan, the addition reaction with epoxy group, or the ionization reaction for the analysis of epoxy compounds Since 1984, many imported epoxy materials have been required to use "hydrogen bromide glacial acetic acid non-aqueous titration" for quality control This method is faster, more accurate and more sensitive than the back titration method of hydrochloric acid acetone which has been widely used for a long time in China It can not only determine common epoxy resins, but also be applied to the rapid determination of fillers or dark epoxy materials Compared with the method of hydrochloric acid acetone, the detection time is shorter The end point is easy to determine, the data is more accurate and centralized, and the scope of application is wide; the effect is equivalent to the perchloric acid method specified in the national standard GB / T 4612, but the use is safer, cheaper and simpler In the production practice of domestic scientific research and production units, the methods of hydrochloric acid acetone, hydrogen bromide glacial acetic acid and perchloric acid were compared and tested The additional description of national standard GB / T 13657-1992 (bisphenol A epoxy resin) is introduced Astm1763-198l (Standard Specification of epoxy resin) is used as reference when the national standard is formulated, and ASTM d1652 (hydrogen bromide glacial acetic acid method) is used to determine the epoxy equivalent The main reason is that the sample needs to be placed for 1H before titration and the reagent needs to be prepared for use; the second reason is that the sample and reagent are well dissolved, react quickly and the end point is easy to be determined because the hydrogen bromide glacial acetic acid method and perchloric acid method are non-aqueous titration, while some samples of the acetone hydrochloric acid method may be slightly poor in the effect of sample dissolution before and after the end point Turbidity, affecting the end point judgment In addition, most of the samples are not transparent resin like E-51 (ep0144l-310 or cyd-128), but mixed with a large number of fillers, colored additives or dark products   For this reason, when the hydrogen bromide glacial acetic acid method is applied in practice, the different epoxy samples are divided into three types of treatment: colorless and transparent samples are in the same steps of 1 and 2; the sample with filler is weighed to 50ml and put into the centrifuge tube, 20ml of trichloromethane or chlorobenzene dissolved samples are added, separated by 0-4000 centrifuge for 5-10min, and the clear solution is taken into the triangular flask for the next test; the colored samples are centrifuged If the separated solution still contains colored substances or the dark color of the product interferes with the titration, the potentiometric titration can be carried out, and the consumed volume can be obtained from the curve by plotting The same method is used to determine two blank samples Compared with perchloric acid method, its principle is the addition reaction between hydrogen bromide and epoxy functional group; the difference is that perchloric acid method is the reaction between perchloric acid and tetraethylamine bromide, the converted hydrogen bromide reacts with epoxy functional group The titrant used in the two methods needs to be calibrated before use, and the calculation method and operation are very similar (hydrogen bromide glacial acetic acid method usually does not consider temperature / volume correction), so the error is small from the results However, hydrogen bromide glacial acetic acid method is easier to obtain and more practical due to the use of reagents All kinds of epoxy materials can be determined by potentiometric titration In general, reagent can be directly used for titration, but due to the volatilization and oxidation of hydrogen bromide and other factors, astmd1052 standard stipulates that perchloric acid and tetraethylamine bromide are used for potentiometric titration, and tetrabutylamine iodide is used for epoxy materials with low activity (the same as the national standard GB / T 4610 perchloric acid method) In fact, this perchloric acid method is another application form of hydrogen bromide glacial acetic acid method, because the test principle is to use perchloric acid and tetraethylamine bromide to react to synthesize the primary hydrogen bromide in situ, and the generated hydrogen bromide reacts with the epoxy group immediately and equivalently The calculation and test methods are the same In the test process, due to the volatile oxidation, the sealed automatic liquid feeding burette can be used The comparison of the test results shows that the self-made reagent is equivalent to the imported reagent, with a deviation of ≤± 1.5%, which can meet the use requirements After the analysis and use of different testers in three laboratories, it is considered that the method and reagent can meet the use requirements of product quality control.