ASTM D 789-98 provides an official, standardized procedure for testing polyamide or nylon molding powders. The higher the molecular weight of the polyamide - that is, the longer the nylon molecules - the higher the viscosity will be at a given concentration in the selected solvent. The larger molecules also contribute more significantly to strength and toughness in the solid molded product compared to the shorter molecules. Therefore, if a material at a specified concentration in solution gives a particular viscosity, then that material will most likely give molded products having correlating properties such as a related level of toughness.
The Brookfield LVT Dial Reading Viscometer is the specified instrument in this method. The sample is contained in an 8 ounce round, wide-mouth screw-cap bottle immersed in a Brookfield TC-501D Circulating Bath. This test can also be performed with other Brookfield Viscometers, such as the LVDV-E, LVDV-I+ and LVDV-II+ PRO in order to save time and minimize error.
* While a particular model/version may be used as an example in this method, any current or past model/version from the same series may also be used. Please consult a sales associate to discuss the most current instrumentation and software available.
The powder is dissolved in either formic acid or m-cresol. The sample temperature is maintained at 25 ±°.1°C The expected viscosities of polyamide solutions and the corresponding spindles at the specified speeds are shown below:
where BVs is the solution's Brookfield viscosity (cP or mPa·s).
The torque reading from the dial is multiplied by the appropriate factor from the following table to provide the viscosity reading in cP:
The Brookfield Digital Viscometers mentioned above provide the viscosity reading in cP directly, so that the user does not need to read %Torque and use the factor tables.