ASTM D789 Determination of Relative Viscosity of Concentrated Polyamide Solutions

Get Certified ASTM D789 Testing for Reliable Polyamide Viscosity Evaluation 

ASTM D789 testing provides a standardized way to evaluate the relative viscosity of concentrated PA solutions. Manufacturers can use these results for quality control, material acceptance, process monitoring, and change evaluation of polyamide materials. The method also allows engineers to evaluate the quality of the material for specific use and to identify changes in the material related to production, storage, or deterioration.

The ASTM D789 standard includes:

• Material type: Concentrated polyamide solutions.
• Purpose: Determine relative viscosity for quality control, acceptance, and material evaluation.
• Property measured: Relative viscosity of the concentrated PA solution.
• Method: Efflux-time method using the viscosity of a required solvent and the density.
• Concentrated-solution solvents: Formic acid and m-cresol, depending on the required polyamide and procedure.
• Dilute solutions: Not covered by this test method.
• Temperature control: The laboratory temperature for viscosity measurement shall comply with the specified test temperature.
• Result: Relative viscosity reported as a dimensionless value.
• Applications: Polyamide quality control, acceptance testing, end-use material evaluation, and determination of deterioration-induced material changes. 

What are the uses of ASTM D789 testing? 

ASTM D789 helps laboratories to assess concentrated polyamide solutions and track changes in the properties of polymer materials. Manufacturers can use the results as part of production and acceptance-control programs. This standard-

• Supports quality-control testing of polyamide materials and provides data for material acceptance testing.
• Helps evaluate polyamide materials for specific end uses and detects changes caused by material deterioration.
• Supports comparison between polymer batches or resin lots. 
• Helps manufacturers monitor changes associated with processing or storage.

Which Materials Can Be Tested Under ASTM D789? 

ASTM D789 relates to polyamide (PA) materials that can be prepared as concentrated solutions in the laboratory. The standard allows samples to be submitted as molding powder, molded shapes, or regrind. Technicians can cut molded specimens into smaller pieces before preparing the solution.

Why is ASTM D789 important? 

Relative viscosity gives a standardized measurement for comparing solutions of concentrated polyamide. ASTM D789 establishes standard conditions for viscometer calibration, solution preparation, temperature control, measurement of efflux time, and calculation procedures. These controls allow laboratories to compare the results from various lots of polyamide resin or to study changes in the material.

ASTM D789 Testing Process and Data Collection

Technicians first collect a representative polyamide sample and ensure proper sample handling conditions. They select the appropriate solvent and prepare the concentrated PA solution. Analysts then calibrate the chosen viscometer with certified viscosity oils. They set the proper temperature in the constant-temperature bath and let the viscometer and test liquid equilibrate. Analysts then measure the time required for the solution to pass between the viscometer timing marks. They take repeated measurements until three consecutive measurements agree within 0.5%. The technician also determines the required density and solvent viscosity information and uses the measured values to calculate relative viscosity.

ASTM D789 Common Challenges and Troubleshooting 

The use of adequate representative sampling, complete dissolution of the polymer, adequate calibration of the viscometer, and consistent timing are all critical in performing relative-viscosity tests. Excessive sample moisture, incomplete dissolution, gel formation, wrong solvent, contamination of the viscometer, temperature instability, wrong calibration, and timing errors are common sample problems. Important steps in the test sequence are identified in the standard as: calibration of equipment, maintenance of controlled temperature, preparation of the solution, and calibration of the viscometers.

• Laboratories report results for temperature in °C, efflux time in (s), density in g/mL, and kinematic viscosity in mm²/s.

• Technicians record the efflux time, solution concentration, solution density, and solvent viscosity data needed to calculate relative viscosity.
• Analysts document the polyamide identification, solution preparation, viscometer calibration, solvent used, test conditions, and measurement configuration during testing.
• Engineers compare the measured relative viscosity with applicable material specifications, control limits, or previous results to evaluate the concentrated polyamide solution and identify significant material changes. 

Link to ASTM D789