Relative Viscosity of PA Solutions – ASTM D 789

Scope:

ASTM D 789 standard The test methods are designed used for control and acceptance testing. They can also be used to assess materials for particular end uses and to identify changes in materials caused by specific forms of deterioration.

Test Procedure:

There are three types of calibrating viscometer procedures in this ASTM D 78:

Calibrating ASTM Ubbelohde (suspended level) type viscometer

Please note that a kinetic energy correction factor needs to be applied to all flow times under 200 seconds. This Size 1 viscometer is employed to determine the absolute viscosity of formic acid. To assess the viscosity of polyamide solutions, use the appropriate ASTM Ubbelohde viscometer, as outlined in accordance with the polyamide viscosity range.
Introduce 10-18 mL of viscosity oil standard into the viscometer using a volumetric pipet. For Size 1 viscometers, employ S-3, while for Size 3 viscometers, use N-100. Submerge the viscometer in a bath set at 25 ± 0.02°C and let it sit for at least 20 minutes. Close off the air arm (not the capillary) and apply air pressure to the large diameter (filling) tube using a rubber bulb. This will cause the oil to fill the capillary above the upper timing mark. Open the air arm and simultaneously let the oil flow downward. This process ensures that the viscometer is properly vetted.
Once again, push the oil above the upper timing mark and note the time (with a precision of 0.2 seconds) it takes for the liquid to descend from the upper timing mark to the lower one. Repeat this procedure until three consecutive readings are in agreement within 0.5%. Record the average value as the
viscosity oil standard at 25°C, denoted as t3 (for S-3) or t100 (for N-100).
Afterwards, take the viscometer out of the bat and thoroughly clean and dry the inner surfaces.

Calibrating the Pipet Viscometer

Please note that a kinetic energy correction factor might be necessary for flow times less than 200 seconds. Utilize Oil S-20 for this calibration. Assemble the pipet viscometer in such a way that the lowest mark on the pipet is aligned with the 50-mL mark on the reservoir of the pipet. Position the assembly within a water bath set to a temperature of 25 ± 0.1°C. After allowing at least 20 minutes, apply air pressure to the reservoir or create a vacuum in the capillary using a rubber bulb.
This action will drive the oil upward into the pipet, surpassing the upper timing mark. Seal the top of the pipet with a finger, and then release the pressure by opening the system to the air. Remove your finger and let the pipet drain.
Repeat this process at least three times to ensure a thorough wetting of the pipet.
Subsequently, note the time (with a precision of 0.2 seconds) it takes for the liquid level to descend from the upper timing mark to the lower one. Determine the efflux time,t20, and repeat this step until three consecutive readings are in agreement within 0.5%. Record the average value. To complete the procedure, follow the same steps using Oil S-60 to obtain T60.

Calibrating the Ostwald (Cannon-Fenske Routine) Viscometer

Please note that a kinetic energy correction factor might be necessary for flow times under 200 seconds. Begin by adding 10 mL of Oil S-3 at approximately 25°C from a volumetric pipet to the viscometer. Submerge the viscometer in a constant-temperature bath set at 25 ± 0.1°C and let it remain there for a minimum of 20 minutes Apply air pressure to the larger diameter leg using a rubber bulb until the oil rises above the upper timing mark. Allow the oil to flow downward. Repeat this process multiple times to guarantee thorough wetting of the viscometer. Once more, push the oil above the upper timing mark, and carefully observe the time (with a precision of 0.2 seconds) needed for the liquid to descend from the upper timing mark to the lower one. Repeat this step until three consecutive readings are within 0.5%. Record the average value for Oil S-3 at 25°C as t3. After completing these steps, remove the viscometer from the bath and meticulously clean and dry the inner surfaces.

Video 01: Determination of Viscosity using Ostwald Viscometer

Test Specimen:

ASTM D 789 Standard Test Method using test specimens for the various tests shall conform to the requirements prescribed herein.

Data:

ASTM D 789 Standard Test Method Determining the efflux time of the standard viscosity Oil

                         ft = dtd

where:
ft = tube factor, mm2/s (cSt)/s,

d = viscosity of S-3 oil, mm2/s (cSt), and

td = efflux time of S-3 oil, s.

Conclusion:

This ASTM D 789 standard test method stands as an essential tool for characterizing the flow behaviour and viscosity of these solutions, offering valuable insights into their molecular structure and processing properties.