ISO 17278:2020 Rubber, raw natural — Determination of the gel content of technically specified rubber (TSR)

ISO 17278:2020 Rubber, raw natural — Determination of the gel content of technically specified rubber (TSR). 8.2.4 After this period, shake the tube up and down for 60 s to disperse the jelly-like precipitate on the bottom. Before placing the tubes in the centrifuge machine, all tubes shall be filled up with fresh toluene, so that the volume of solution is the same in all tubes. NOTE A centrifuge tube is usually filled up with solution to minimize the dead space created at the top of the tube because of the vacuum-pressured environment during rotation. Place the tubes in the centrifuge machine and operate the machine at 14 000 r/min for 2 h. If the rotating capacity of the centrifuge machine is below 14 000 r/rnin, operate the machine at 8 000 r/ minfor6h. A set temperature of centrifuge is usually indicated in the operation manual for safety reasons. If not, it may be set to between 0 °C and 25 °C. 8.2.5 Remove the tube from the machine and pipette the liquid from the tube held at approximately 45°. Caution shall be taken to prevent pipetting the precipitate. 8.2.6 Add 1 ml to 3 ml of acetone to the precipitate so that it can be easily peeled from the bottom of the tube. Leave to stand for over 30 s and then pipette the liquid from the tube. 8.2.7 Peel off the precipitate remaining at the bottom of the tube with a spatula or a spatula-like stick and move it into the container (ft5) which has been cleaned and weighed to the nearest 1 mg (m1). A limited amount of acetone may be used to rinse the spatula, if necessary. 8.2.8 Store the container in a fume cupboard for 30 mm to allow the solvent to evaporate, in order to prevent flashing of the solvent during heating. Place the container containing the precipitate in the oven and dry it at the temperature of 110 °C for 1 h. 8.2.9 Take the container out of the oven and allow it to cool in a desiccator for 30 mm. 8.2.10 Weigh the container containing the dry precipitate to the nearest 0,1 mg (m2). 8.2.11 Repeat the procedure in 11.2.8, 8.2.9 and 11.2W) until the loss in mass between two successive weighings is less than 0,2 mg. Note the period of drying time for the first test piece and use it for...