ISO 247-1:2018 pdf download – Rubber – Determination of ash
8.1 Method
A Heat a clean empty crucible (6.1) of appropriate size for about 30 min in the muffle furnace (6.4), maintained at 550 °C ± 25 °C, allow to cool to ambient temperature in a desiccator and weigh to the nearest 0,1 mg. Take a test portion of about 5 g of raw rubber or 1 g to 5 g of compounded rubber or vulcanizate, according to the mass of ash to be expected, and weigh to the nearest 0,1 mg. Place the weighed test portion in the crucible mounted in the hole in the heat-resistant, thermally insulating board (6.2). Heat the crucible gently with the burner (6.3) in a hood for proper ventilation, taking care that the rubber does not ignite. If any material is lost due to spurting or frothing, repeat the above procedure with a new test portion. When the rubber has decomposed to a charred mass, gradually increase the heat from the burner until the volatile decomposition products have been substantially expelled and a dry carbonaceous residue remains. Transfer the crucible and its contents to the muffle furnace, maintained at 550 °C ± 25 °C (for compounds and vulcanizates, a temperature of 950 °C ± 25 °C may be used), leaving the door of the furnace slightly open for 1 min to provide sufficient air to oxidize the carbon. Continue heating until the carbon is completely oxidized and a clean ash is obtained. Remove the crucible and its contents from the furnace, allow to cool to ambient temperature in the desiccator and weigh to the nearest 0,1 mg. Then heat the crucible and its contents again for about 30 min in the muffle furnace, maintained at 550 °C ± 25 °C (for compounds and vulcanizates, a temperature of 950 °C ± 25 °C may be used), allow to cool to ambient temperature in the desiccator and re-weigh to the nearest 0,1 mg. This mass shall not differ from the previous mass by more than 1 mg in the case of raw rubbers or by more than 1 % relative to the amount of ash for compounds and vulcanizates.
8.2 Method B
Heat a clean empty crucible (6.1) of appropriate size for about 30 min in the muffle furnace (6.4), maintained at 950 °C ± 25 °C, allow to cool to ambient temperature in a desiccator and weigh to the nearest 0,1 mg. Take a test portion of about 1 g to 5 g of the compound or vulcanizate and weigh to the nearest 0,1 mg. Place the test portion in the crucible and pour about 3,5 cm 3 of concentrated sulfuric acid (5.1) over it so that the rubber is completely wetted. Place the crucible and its contents in the hole in the heat-resistant, thermally insulating board (6.2) and heat gently with the burner in a hood for proper ventilation. If, during the initial reaction, the mixture swells excessively, withdraw the flame to avoid possible loss of material.
When the reaction becomes more gentle, increase the heat from the burner until the excess sulfuric acid is volatilized and a dry, carbonaceous residue remains. Transfer the crucible and its contents to the muffle furnace, maintained at 950 °C ± 25 °C, leaving the door of the furnace slightly open for 1 min to provide sufficient air to oxidize the carbon and heat for about 1 h until all the carbon is completely oxidized and a clean ash is obtained. Remove the crucible and its contents from the furnace, allow to cool to ambient temperature in a desiccator and weigh to the nearest 0,1 mg. Then heat the crucible and its contents again for about 30 min in the muffle furnace, maintained at 950 °C ± 25 °C, allow to cool to ambient temperature in the desiccator and re-weigh to the nearest 0,1 mg.