BS ISO 125:2020 pdf download.Natural rubber latex concentrate — Determination of alkalinity.
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 976, Rubber and plastics — Polymer dispersions and rubber latices Determination of pH
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Principle
A test portion of latex concentrate is titrated with acid to pH 6 in the presence of a stabilizer to prevent coagulation, either electrometrically or with methyl red as a visual indicator. The alkalinity is calculated from the quantity of acid required.
5 Reagents
Use distilled water or water of equivalent purity, wherever water is specified, and reagents of recognized analytical quality.
5.1 Stabilizer solution: 5 % (by mass) solution of a non-ionic stabilizer of the alkyl phenol polyethylene oxide condensate type. Before use, the pH of the solution shall be adjusted to a value of 6,0±0,05.
5.2 Sulfuric acid, c(H2S04) = 0,05 mol/dm3, or hydrochloric acid, c(HCI) = 0,1 mol/dm3, standard volumetric solution.
5.2.1 Standardization of sulfuric acid, standardize 0,05 mol/dm3 H2S04 by pipetting 10 cm3 of
0,05 mol/dm3 Na2CO3 solution (5.5) into a flask and titrating with 0,05 mol/dm3 H2S04, using methyl orange (5.4) as indicator
5.2.2 Standardization of hydrochloric acid, standardize 0,1 mol/dm3 HC1 by pipetting 10 cm3 of
0,05 mol/dm3 Na2CO3 solution (5,5) into a flask and titrating with 0,1 mol/dm3 I-Id, using methyl orange
(SA) as indicator.
5.3 Methyl red, 0,1 % solution in ethanol of minimum purity 95 % (by volume).
5.4 Methyl orange, 0,1 % solution in ethanol of minimum purity 95 % (by volume).
5.5 Sodium carbonate solution, c(Na2CO3) = 0,05 mol/dm3.
Dry the Na2CO3 used to prepare this solution at 120 °C ± 5 °C for 2 h before preparing the solution,
6 Apparatus
Standard laboratory equipment together with:
6.1 Electrical stirrer, with earthed (grounded) motor and non-metallic propeller-type blade, or magnetic stirrer.
6.2 pH-meter, equipped with a combined electrode suitable for use in solutions up to pH 12, as specified in ISO 976. and capable of being read to 0,02 pH-units.
6.3 Balance, capable of being read to 0,01 g.
7 Sampling
Carry out sampling in accordance with one of the methods specified in ISO 123.
8 Procedure
8.1 General
Carry out the determination in duplicate.
Add, while stirring, 10 cm3 of stabilizer solution (Sd) to about 200 cm3 of water in a 400 cm3 beaker. Weighing to the nearest 10 mg, add between 5 g and 10 g of the latex concentrate by difference from a weighing bottle and stir until thoroughly mixed.
Ensure that the latex is added so that none runs down the side of the beaker (which could result in loss of ammonia) or down the side of the weighing bottle.
Titrate the resulting mixture either by the method described in 82 or by that described in 83.BS ISO 125 pdf download.