BS ISO 14558:2016 pdf download – Rubber — Determination of residual unsaturation of hydrogenated nitrile butadiene rubber (HNBR) by infrared spectroscopy
1 Scope This International Standard specifies a method for determining the residual unsaturation in hydrogenated nitrile rubber (HNBR) by measuring the infrared (IR) absorbance of HNBR films cast from solution. This International Standard assumes that samples and IR spectra are prepared and analysed by experienced personnel and that equipment is operated in accordance with the manufacturer’s instructions. Details for operating an IR spectrometer are not included in this method.
2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 1795, Rubber, raw natural and raw synthetic — Sampling and further preparative procedures
3 Principle Raw, unvulcanized HNBR is purified by precipitation with methanol from a solution in methyl ethyl ketone (MEK) or by extraction of the solid HNBR with methanol in a Soxhlet apparatus. The purified sample is dissolved in MEK and a film is cast on a potassium bromide (KBr) disc. The IR spectrum of the film is obtained with a Fourier-transform (FT) or dispersive IR spectrometer. The “corrected absorbance” of the specific absorbance bands for acrylonitrile (AN), butadiene (BD) and hydrogenated butadiene (HBD) are determined using the baseline method and the percentage of residual unsaturation (double bonds in unhydrogenated butadiene) is calculated with the aid of absorbance factors from the literature (see 8.5). 4 Reagents Reagent grade chemicals should preferably be used in all determinations. Other grades may be used provided that they are of sufficiently high purity not to lessen the accuracy of the determination.
4.1 Methyl ethyl ketone (MEK).
4.2 Methanol.
4.3 Dry, compressed nitrogen.
4.4 Potassium bromide discs.
5 Sampling
Sample the raw rubber in accordance with ISO 1795.
6 Apparatus
Ordinary laboratory equipment and the following.
6.1 Conical flask, 50 cm 3 , with ground-glass stopper.
6.2 Flask shaker.
6.3 Beaker, 250 cm 3 .
6.4 Magnetic stirrer.
6.5 Soxhlet extraction apparatus, with 150 cm 3 flask.
6.6 Extraction thimbles, 25 mm × 100 mm.
6.7 Koffler heating bench, or other heating device, with temperature control to ±2 °C.
6.8 Fourier-transform IR (FTIR) spectrometer, with 2 cm −1 resolution or a dispersive IR spectrometer capable of equivalent spectral resolution. The instrument shall be capable of scale expansion along the absorbance or transmittance axis over the special region of 2 500 cm −1 to 600 cm −1 .
7 Procedure
7.1 Sample preparation
7.1.1? Purification by precipitation Transfer 1 g of the finely divided HNBR rubber sample into a 50 cm 3 conical flask. Add 20 cm 3 of MEK to the flask. Tightly stopper the flask and place it on a flask shaker and shake until the sample has completely dissolved. Precipitate the rubber by slowly pouring the MEK solution into a 250 cm 3 beaker containing 150 cm 3 of methanol, while rapidly stirring the methanol with a magnetic stirrer. Decant the solvent and wash the precipitated rubber with 50 cm 3 of methanol. Decant the methanol washings and redissolve the precipitated rubber in 20 cm 3 of MEK.
7.1.2 Purification by extraction
Transfer 1 g of finely divided rubber into an extraction thimble and extract for 6 h in a Soxhlet apparatus with 100 cm 3 of methanol.
Remove the extracted sample from the thimble and dissolve in 20 cm 3 of MEK.
7.1.3 Cast a smooth film from the MEK solution (see or 7.1.2) on a KBr disc. On a Koffler, or similar, heating device, in a well-ventilated hood under a stream of nitrogen, carefully evaporate the MEK solvent from the cast film, taking care not to heat the film over 100 °C. The thickness of the film shall be chosen so that the absorbance A of the band at 2 236 cm −1 is <0,8 A. With dispersion spectrometers and an unsaturation of <1 %, films shall exhibit an A (2 236) of between 0,7 and 0,8.
7.2 Obtaining the IR spectrum Obtain the spectrum with an FTIR spectrometer with 2 cm −1 resolution, collecting 50 scans, or with a dispersive IR spectrometer and appropriate scan parameters. NOTE Appearance of a band at approximately 1 730 cm −1 indicates residual MEK and a band at 696 cm −1 indicates inadequate purification.BS ISO 14558 pdf download.