ISO 127:2012 pdf download – Rubber, natural latex concentrate – Determination of KOH number
1 Scope
This International Standard specifes a method for the determination of the KOH number of natural rubber latex concentrate which is preserved wholly or in part with ammonia. The method is applicable to latices containing boric acid. The method is not applicable to latices preserved with potassium hydroxide. It is not necessarily suitable for latices from natural sources other than Hevea brasiliensis, or for latices of synthetic rubber, compounded latex, vulcanized latex or artifcial dispersions of rubber.
2 Normative references
The following referenced documents are indispensable for the application 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 125, Natural rubber latex concentrate — Determination of alkalinity
ISO 976, Rubber and plastics — Polymer dispersions and rubber latices — Determination of pH
ISO 1802, Natural rubber latex concentrate — Determination of boric acid content
3 Terms and defnitions
For the purposes of this document, the following terms and defnitions apply.
3.1 KOH number
<rubber latex> number of grams of potassium hydroxide equivalent to the acid radicals combined with ammonia in latex containing 100 g of total solids [ISO 1382:2008]
4.3 Formaldehyde, 45 g to 50 g in 1 dm 3 of solution [c(HCHO) = 1,5 mol/dm 3 to 1,67 mol/dm 3 ], acid-free, prepared by diluting concentrated formaldehyde with water and neutralizing with 0,1 mol/dm 3 potassium hydroxide solution (4.1), using as indicator the faint pink colour of phenolphthalein.Determine the concentration of the formaldehyde solution as described in Annex A.
5 Apparatus
Standard laboratory glassware, plus the following:
5.1 pH-meter, conforming to ISO 976 but capable of being read to 0,01 units.
5.2 Glass electrode, of a type suitable for use in solutions of pH up to 12,0.
5.3 Mechanical stirrer, with earthed motor and glass paddle, or magnetic stirrer.
An automatic titrator may be used provided it has been checked as giving the same result as the standard method.
6 Sampling
Carry out the sampling in accordance with one of the methods specifed in ISO 123.
7 Procedure
Calibrate the pH-meter by the method specifed in ISO 976. If the total solids (w TS ) and alkalinity (A) of the latex are not known, determine them in accordance with ISO 124 and ISO 125, respectively. If the latex contains boric acid and the content is not known, determine it in accordance with ISO 1802.
Carry out the determination in duplicate.
Weigh, to the nearest 0,1 g, into a 400 cm 3 beaker a test portion (mass m) of the test sample containing approximately 50 g of total solids. If necessary, adjust the alkalinity to (0,5 ± 0,1) % ammonia calculated with respect to the water phase by adding, while stirring, the required quantity of formaldehyde solution (4.3).
If the initial pH is less than 10,3, slowly add 5 cm 3 of 0,5 mol/dm 3 potassium hydroxide solution (4.2) while stirring slowly with the glass paddle or magnetic stirrer (5.3). Record the resultant equilibrium pH reading. With continued stirring, add 0,5 mol/dm 3 potassium hydroxide solution (4.2) in 1 cm 3 increments at regular (e.g. 15 s) intervals, recording the resultant equilibrium pH after each addition. Continue until the end-point has been passed.