ISO 3681:1996 download.Binders for paints and varnishes – Determination of saponification value Titrimetric method.
1 Scope
ISO 3681 specifies a titrimetric method for determining the esterifieci-acid content in binders for paints and varnishes, free acids and acid anhydrides being necessanly included in the result obtained.
Because different binders vary in their resistance to saponification, ISO 3681 is of limited applicability. If necessary, completeness of saponification may be checked by repeating the test under more severe conditions achieved by the use of longer saponification time, more concentrated potassium hydroxide solution, or a higher-boiling alcohol as solvent.
Annex A specifies a procedure suitable for binders that saponify with difficulty.
The method is not applicable to those materials that show further reaction with alkalis beyond normal saponification.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of ISO 3681. At the time of pubcation, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on ISO 3681 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 385-1:1984, Laboratory glassware — Burettes — Part 1: General requirements.
ISO 648:1977. Laboratory glassware — One-mark pipertes.
ISO 842:1984, Raw materials for paints and varnishes — Sampling.
ISO 36961987, Water for analytical laboratory use — Specification and test methods.
3 Definitions
For the purposes of ISO 3681, the following definitions apply.
3.1 saponification: The formation of the alkali metal salts of derivatives of organic acids.
3.2 saponification value: The number of rnhlligrdms of potassium hydroxide (KOH) required for the saponification of 1 g of the product tested.
4 Principle
After a preliminary test to determine the saponification conditions concentration of potassium hydroxide solution, saponification time, etc.) for the product to be tested, a test portion is boiled under roflux with potassium hydroxide solution under these conditions. The hot solution is titrated with standard volumetric hydrochloric acid, either in the presence of a colour indicator or potentiometrically.
5 Reagents
During the analysis, use only reagents of recognized analytical grade, and only water of at least grade 3 purity as defined in ISO 3696.
5.1 Toluene, or other suitable unsaponifiable solvent.
5.2 Potassium hydroxide solution, in isopropanol. ethanol or methanol, c(KOH) = 0.5 mol/l.
NOTE 1 Il more severe conditions for saponification are needed. 2 mcI/I ethanolic potassium hydroxide solution may be used, or 1 ,2-ethanediol (ethylene glycol) or 2.2’ oxydiethanol (diethylene glycol) may be used as the solvent (see clause 8 and annex A)
Where isopropanol can be used instead of ethanol or methanol, it shall be used. The applicability of the solution in isopropanol is comparable to that of an ethanolic solution and its toxicity is less than that of a methanolic solution.
5.3 Hydrochloric acid, standard volumetric solution, c(HCI) = 0.5 mol1, in a mixture of 4 parts by volume of methanol and 1 part by volume of water or in water.
5.4 Phenolphthalein or thymolphthalein, 10 g/l solution in 95 % (V/V) ethanol, in methanol or in isopropanol (see note 1).
6 Apparatus
Ordinary laboratory apparatus and glassware, complying with the requirements of ISO 385-1 and ISO 648. together with the following:
6.1 ConIcal flask, of capacity 250 ml, with a ground- glass joint.
6.2 Ref lux condenser, with a ground-glass joint.
6.3 Burette or pipette, of capacity 25 ml or 50 ml.
6.4 Potentiometrlc titration apparatus, fitted with
a glass electrode and a reference electrode. The use
of this apparatus is an optional alternative (see 9.2).
6.5 Magnetic stirrer.
6.6 Water bath or oil bath.
7 Sampling
Take a representative sample of the product to be tested, as described in ISO 842.
8 Preliminary test
If no special saponification conditions are specified or agreed, carry out the procedure specified in clause 9 using 25 ml of potassium hydroxide solution (5.2) and a boiling time of 1 h. To test whether the saponification value can be determined under these conditions, intensify the conditions by increasing the saponifica
tion time to at least 2 h and/or by using a 2 mol/l potassium hydroxide solution or a solution of potassium hydroxide in an alcohol that has a boiling point distinctly higher than that of ethanol, for example 1.2. ethanediol (ethylene glycol) or 2,2’-oxydiethanol (diethylene glycol).
If no increase in the final (i.e mean) result (see 10.1) is obtained using the more intense conditions, the test may be carried out using ISO 3681. If a higher value s obtained which is not further increased by again intensifying the test conditions, ISO 3681 may be followed but using and noting the intensified concirtions applied. If a constant result is not obtained even under the most severe conditions of saponification, the method to be used shall be agreed between the interested parties.
9 Procedure
Carry out the determination in duplicate.
9.1 Test portion
By reference to table 1, select the appropriate mass of test portion to be taken. This mass shall be chosen so that less than half of the volume of potassium hydroxide solution added is sufficient to saponify the Lest puiLiuri.
a) 25 ml of 0.5 molIl potassium hydroxide solution
(5.2):
b) 25 ml of a different potassium hydroxide solution (see clause 8 and note 1 to 5.2);
C) the specified or agreed volume of a potassium hydroxide solution.
Heat, while stirring, the contents of the flask to boiling in a water bath or oil bath (6.6) and ref lux for 1 h or the specified or agreed time, or the time found necessary in the preliminary test (see clause 8).
Titrate the hot solution with hydrochloric acid (5.3) after addition of 3 drops of phenolphthalein or thymolphihalein solution (5.4).
If the potentiometric titration is used, the glass electrode shall have a suitable response time.
If precipitation occurs, bring the precipitate back into solution by the addition of water, which acts as a solvent.
9.3 Blank test
Carry out a blank test, following the same procedure but omitting the test portion.
10 Expression of results
10.1 Calculation
Calculate the saponification value SV, in milligrams of KOH per gram of product, using the equation
SV=”’O -V1)xcx56,1
where
V0 is the volume, in millilitres, of hydrochloric acid (5.3) required for the blank test (9.3),
V1 is the volume, in millilitres, of hydrochloric acid (5 3) required for the determination
(9.2);
c is the actual concentration, in moles per litre, of the hydrochloric acid (5.3);
56,1 is the factor for the conversion of millilitres of hydrochloric acid, c(HCI) = 1 mol/l, to milligrams of potassium hydroxide;
m is the mass, in grams, of the test portion
(9,1).
If the two results (duplicates) differ by more than 3 %
(relative to the mean), repeat the procedure described
in clause 9.
Report as the final result the mean, rounded to the nearest 0.1 mg KOH/g, of two valid results (replicates).
10.2 Precision
No precision data are currently available.
11 Test report
The test report shall contain at least the following information:
a) all details necessary to identify the product tested;
b) a reference to this International Standard
(ISO 3681);
c) the re5ult of the test as indicated in 10.1;
d) the solvent and the concentration and volume of the potassium hydroxide sululion used;
e) the period of boiling:
f) the type of titration: in the presence of a colour indicator (phenolphthalein or thymolphthalesn) or potentiometric;
g) any deviation from the test method specified.
h) the date of the test,