Relative Viscocity of Polyamide

(Brookfield Method) ASTM D789, D4878

Introduction:

Viscosity is a fundamental property of materials that describes their resistance to flow. In particular, viscosity is a measure of the internal resistance to shear within a material, and can be used to characterize the consistency and quality of products. In addition, viscosity can also be used to compare the degradation of molded parts with the original resin, as degradation can result in a reduction of molecular weight and therefore a decrease in viscosity.

Experimental Method:

To measure the viscosity of a polymer, a sample of 22.0 +/- 0.01 grams of polymer is dissolved in formic acid in an 8 oz screw cap bottle. The solution is agitated on a shaker until complete dissolution is achieved, and then placed in a 25°C bath for at least 1 hour. The resulting solution is then placed in a Brookfield Viscometer, and the appropriate spindle speed is selected based on the expected viscosity of the sample. The Brookfield Viscometer measures viscosity by determining the force required to rotate the spindle in the solution at a given rate.

Data Analysis:

The relative viscosity of the polymer solution is calculated by dividing the absolute viscosity of the polymer-formic acid solution by the absolute viscosity of the formic acid. The relative viscosity is expressed as:

Rv = (Ms/Mf)

Where Rv is the relative viscosity of the polymer-formic acid solution, Ms is the absolute viscosity of the solution, and Mf is the absolute viscosity of the formic acid.

Conclusion:

Viscosity is a useful property for characterizing the consistency and quality of products, as well as for assessing the degradation of molded parts. The method described here provides a straightforward means of measuring viscosity using a Brookfield Viscometer and a polymer-formic acid solution. The resulting relative viscosity can be used as an indicator of the material's properties.