ISO 506-2020 pdf free download – Rubber latex, natural, concentrate — Determination of volatile fatty acid number.
This document specifies a method for the determination of the volatile fatty acid number of naturalrubber latex concentrate.The method is not necessarily suitable for latices from natural sources otherthan Hevea brasiliensis and is not applicable to compounded latex, vulcanized latex, artificialdispersionsof rubber or synthetic rubber latices.
2Normative references
The following documents are referred to in the text in such a way that some or all of their contentconstitutes requirements of this document. For dated references, only the edition cited applies. Forundated references, the latest edition of the referenced document (including any amendments) applies.IS0 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.
lSO 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 numberVFA
number of grams of potassium hydroxide equivalent to the volatile fatty acids in latex concentratecontaining 100 g of total solids
Note 1 to entry: If the substances have been added to the latex which produce volatile acids on acidification withsulfuric acid, the volatile fatty acid number is high and does not represent the volatile fatty acid content withoutcorrection.
4 Principle
A test portion is coagulated with ammonium sulfate and a portion of the resultant serum is separatedand acidified with sulfuric acid.The acidified serum is steam-distilled and the volatile acids presentin the test portion are determined by titration of the distillate with a standard volumetric bariumhydroxide solution.
5Reagents
During the analysis, use only reagents of recognized analytical quality and only distilled water or waterof equivalent purity.
5.1Ammonium sulfate, approximately 30 % (mass fraction) solution.5.2Sulfuric acid, approximately 50 % (mass fraction) solution.
5.3 Barium hydroxide, standard volumetric solution,c[Ba(OH),] = 0,005 mol/dm3, standardizedby titration with potassium hydrogen phthalate and stored in the absence of carbon dioxide. In case offinding 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.
5.5Silicone antifoaming agent, if necessary.
5.6Calcium hydroxide, approximately 5 % (mass fraction) solution.
6Apparatus
Use ordinary laboratory apparatus and the following.
6.1 Steam-jacketed distillation apparatus (Markham still), as presented in Figure 1 and Table 1.Asan alternative to the one-piece apparatus illustrated in Figure 1, a ground-glass joint may be insertedbetween the distillation vessel and the condenser.
6.2Steam-bath.
6.3Water-bath, capable of being maintained at a nominal temperature of 70 °C.6.4Pipettes, of capacity 5 cm3, 10 cm3, 25 cm3and 50 cm3.
6.5 Burette, of suitable capacity.
6.6Qualitative filter paper, of medium particle retention and medium flow rate.6.7Air pump, of air flow at least 200 cm3/min.ISO 506 pdf download.