Determination of Relative Viscosity of Polyamide (PA) (Brookfield Method) ASTM D789, D4878

Viscosity is the property of resistance to flow exhibited within the body of a material at a given shear rate. Flow behavior is an indirect measure of product consistency and quality where materials must be consistent from batch to batch. Also, molded parts can be compared to original resin to determine the extent of degradation from the molding process since degraded material would be lower in viscosity as a result of reduced molecular weight. This is a sensitive method for material characterization because flow behavior is responsive to molecular weight and molecular weight distribution.

Test Procedure:
Formic acid is added to an eight ounce screw cap bottle filled with 22.0 +/- 0.01 grams of polymer. All is agitated on a shaker until the nylon is in solution, then placed in a 25°C bath for not less than 1 hour. The prepared solution is placed in the Brookfield Viscometer and a proper speed is selected for the spindle according to the expected viscosity of the sample. The Brookfield Viscometer determines viscosity by measuring the force to turn the spindle in the solution at a given rate.

Relative Viscosity is calculated by dividing absolute viscosity of the nylon/formic acid solution by the absolute viscosity of the formic acid.

Rv = relative viscosity of nylon-formic acid solution.
Mf = absolute viscosity of formic acid.
Ms = absolute viscosity of nylon-formic acid solution.

Rv = (Ms/Mf) 

**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Due to copyright restrictions, we are not able to provide copies of standards. Standards can be obtained from appropriate standards authorities.
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