ISO 506:2020 pdf download – Rubber latex, natural, concentrate — Determination of volatile fatty acid number.
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 123, Rubber latex — Sampling ISO 124, Latex, rubber — Determination of total solids content ISO 126, Natural rubber latex concentrate — Determination of dry rubber content 3? Terms? and? definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https:// www .iso .org/ obp — IEC Electropedia: available at http:// www .electropedia .org/ 3.1 volatile fatty acid number VFA number of grams of potassium hydroxide equivalent to the volatile fatty acids in latex concentrate containing 100 g of total solids Note 1 to entry: If the substances have been added to the latex which produce volatile acids on acidification with sulfuric acid, the volatile fatty acid number is high and does not represent the volatile fatty acid content without correction. 4 Principle A test portion is coagulated with ammonium sulfate and a portion of the resultant serum is separated and acidified with sulfuric acid. The acidified serum is steam-distilled and the volatile acids present in the test portion are determined by titration of the distillate with a standard volumetric barium hydroxide solution.
5.1 Ammonium sulfate, approximately 30 % (mass fraction) solution. 5.2 Sulfuric acid, approximately 50 % (mass fraction) solution. 5.3 Barium hydroxide, standard volumetric solution, c[Ba(OH) 2 ] = 0,005 mol/dm 3 , standardized by titration with potassium hydrogen phthalate and stored in the absence of carbon dioxide. In case of finding barium carbonate sediment in the standard solution, re-standardization is recommended. 5.4 Indicator solution, either bromothymol blue or phenolphthalein solution, 0,5 % (mass fraction) in a mixture of approximately equal volumes of ethanol and water. 5.5 Silicone antifoaming agent, if necessary. 5.6 Calcium hydroxide, approximately 5 % (mass fraction) solution. 6 Apparatus Use ordinary laboratory apparatus and the following. 6.1 Steam-jacketed distillation apparatus (Markham still), as presented in Figure 1 and Table 1. As an alternative to the one-piece apparatus illustrated in Figure 1, a ground-glass joint may be inserted between the distillation vessel and the condenser. 6.2 Steam-bath. 6.3 Water-bath, capable of being maintained at a nominal temperature of 70 °C. 6.4 Pipettes, of capacity 5 cm 3 , 10 cm 3 , 25 cm 3 and 50 cm 3 . 6.5 Burette, of suitable capacity. 6.6? Qualitative? filter? paper, of medium particle retention and medium flow rate. 6.7 Air pump, of air flow at least 200 cm 3 /min.