ISO 3681:1996 pdf download – Binders for paints and varnishes – Determination of saponification value – Titrimetric method
1 Scope
This International Standard specifies a titrimetric method for determining the esterified-acid content in binders for paints and varnishes, free acids and acid anhydrides being necessarily included in the result ob- tained. Because different binders vary in their resistance to saponification, this International Standard is of limited applrcability. If necessary, completeness of saponifi- cation may be checked by repeating the test under more severe conditions achieved by the use of longer saponifrcatron time, more concentrated potassium hy- droxide 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 sap- onification.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions Indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to in- vestigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid In- ternational Standards.
ISO 385-l :I 984, Laboratory glassware – Burettes – Part 1: General requirements.
ISO 648:1977, Laboratory glassware – One-mark pip- ettes.
4 Principle
After a preliminary test to determine the saponifi- cation conditions (concentration of potassium hydrox- ide solution, saponification time, etc.) for the product to be tested, a test portion is boiled under reflux with potassium hydroxide solution under these conditions. The hot solution is titrated with standard volumetric hydrochloric acid, either in the presence of a co/our indicator or potentiometrically.
NOTE 1 If more severe conditions for saponification are needed, 2 mol/l 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 sol- ution in isopropanol is comparable to that of an etha- nolic solution and its toxicity is less than that of a methanolic solution.
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 saponifica- tion value can be determined under these conditions, intensify the conditions by increasing the saponifica- 0 IS0 tion time to at least 2 h and/or by using a 2 mol/l po- tassium hydroxide solution or a solution of potassium hydroxide in an alcohol that has a boiling point dis- tinctly higher than that of ethanol, -for example 1,2- ethanediol (ethylene glycol) or 2,2’-oxydiethanol (diethylene gtycol). 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 this International Standard. If a higher value is obtained which is not further in- creased by again intensifying the test conditions, this International Standard may be followed but using and noting the intensified conditions 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.