BS ISO 506:2020 pdf download.Rubber latex, natural, concentrate — Determination of volatile fatty acid number.
7 Sampling
Carry out the sampling in accordance with one of the methods specified in Iso 123.
8 Procedure
8.1 lithe total solids content and dry rubber content of the latex concentrate are not known, determine them in accordance with ISO 124 and ISO 126, respectively.
8.2 Into a beaker weigh, to the nearest 0,1 g, about 50 g of latex concentrate. Accurately add 50 cm3 of the ammonium sulfate solution (Si.) from a pipette (6.4), while stirring the latex concentrate. Either place the beaker on the steam-bath (62) or in the water-bath (6.3), maintained at 70°C, and continue stirring the latex concentrate until it coagulates. Cover the beaker with a watch-glass and leave it on or in the bath for a total period of 15 mm.
Decant the serum which exudes through a dry filter paper (fi4). Transfer the coagulum to a mortar and press out more serum by kneading it with a pestle. Filter this serum through the same filter. Pipette 25 cm3 of the filtered serum in a dry 50 cm3 conical flask and acidify it by accurately adding 5 cm3 of the sulfuric acid solution (52). Mix well by swirling the flask.
With certain latex concentrates, in particular those preserved with potassium hydroxide, a fine precipitate may form during the acidification step. This precipitate shall be removed by filtration through a fresh dry filter paper before proceeding with the distillation process.
Pass steam through the apparatus (6.1) for at least 15 mm. With steam passing through the outer jacket of the apparatus (steam outlet open), introduce into the inner tube 10 cm3 of the acidified serum by pipette (6A). If foaming is a difficulty, one drop of a suitable aritifoaming agent (IS) may be added. Place a 100 cm3 graduated cylinder under the tip of the condenser to receive the distillate. Partially close the steam outlet to divert steam into the inner tube. Pass steam gently at first, then fully close the steam outlet and continue distilling at a rate of 3 cm3/min to 5 cm3/min until 100 cm3 of distillate has been collected.
Transfer the distillate to a 250 cm3 conical flask and eliminate any dissolved carbon dioxide from the distillate by using air pump 61) which outlet air at a rate of 200 cm3/min to 300 cm3/min passes into calcium hydroxide saturated solution (16) before passing through the distillate for approximately 3 mm. Titrate with the barium hydroxide solution (5.3), using one of the indicators specified (14). If bromothymol blue is used as indicator, the colour changes from yellow to blue and, if phenolphthalein is used as indicator, the colour changes from colourless to pale pink.
8.3 Carry out a duplicate determination (see 82) with a fresh 50 g test portion of latex concentrate.BS ISO 506 pdf download.