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Significance and Use
The iodine value of a fatty acid product is a measure of the unsaturated fatty acid content of that product and consequently a measure of the ease of oxidation or drying capacity of that fatty acid product.
This test method measures the unsaturation as iodine value by addition of an iodine/chlorine reagent. The amount of reagent absorbed is determined by back titrating the excess reagent and comparing it to a blank determination.
In samples containing conjugated double bonds, the iodine value obtained is empirical since the reagent does not react stoichiometrically with conjugated unsaturation. Where no conjugation is present, the iodine value obtained is a measure of the total unsaturation. By using proper specimen weights, the empirical values obtained are useful for comparative purposes.
This test method was developed in order to replace the hazardous solvent, carbon tetrachloride, used in Test Method D1959 with the less hazardous and more available solvents, iso-octane and cyclohexane. As data on the satisfactory use of other solvents becomes available, this test method will be amended to include those solvents.
This test method should have applicability to fatty acids and oils other than tall oil fatty acid but that possibility has not been investigated.
1.1 This test method covers the Wijs procedure for determination of unsaturation (iodine value) of tall oil fatty acids.
1.2 Iodine value is a measure of the unsaturation of oils and fatty acids and is expressed in terms of the number of centigrams of iodine per gram of sample (weight percent of absorbed iodine).
1.3 When this test method is used to determine the iodine value of fatty acids having conjugated systems, the result is not a measure of total unsaturated, but rather is an empirical value that affords a comparison of unsaturation. Total unsaturation of conjugated systems may be measured in accordance with Test Method D1541.
1.4 The test method described here is not reliable for tall oil fatty acids containing an appreciable quantity of rosin.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D1193 Specification for Reagent Water
D1541 Test Method for Total Iodine Value of Drying Oils and Their Derivatives
D1959 Test Method for Iodine Value of Drying Oils and Fatty Acids
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
ICS Number Code 87.060.20 (Binders)
UNSPSC Code 13111103(Tall oil rosin)
ASTM D5768-02(2010), Standard Test Method for Determination of Iodine Value of Tall Oil Fatty Acids, ASTM International, West Conshohocken, PA, 2010, www.astm.orgBack to Top