ASTM D3616 – Standard Test Method for Rubber—Determination of Gel, Swelling Index, and Dilute Solution Viscosity
Description:
Significance and Use
4.1 These tests are particularly useful for quality control in the production of synthetic rubbers.
4.2 Percent gel is a measure of the amount of insoluble rubber present in the chosen solvent. Gel may be introduced intentionally in some rubbers. Variations from a normal level indicate changes in the polymerization system.
4.3 Swelling index is a measure of the type of gel. Gel with a low-swelling index is referred to as “hard gel” and usually indicates the presence of material that does not break down readily by milling. A high-swelling index normally indicates the presence of a “loose gel” that may be broken down easily by milling.
4.4 In low-gel or gel-free rubbers, the DSV correlates directly with the molecular weight. Since the viscosity is measured only on the soluble portion of the rubber, the use of DSV to predict molecular weight in rubbers having high gel values is meaningless.
Scope
1.1 This test method covers the determination of the dilute solution viscosity (DSV), the gel characteristics, and the swelling index of raw non-oil-extended and non-pigmented SBR and NBR.
1.2 This test method may be used to determine the DSV and gel characteristics of rubbers other than SBR and NBR, however, solvents other than 2-butanone and toluene may be required.
1.3 This test method is not intended for the measurement of micro-gel.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
ASTM D3612