Technical Standard
Technical standards defining the measurement of viscosity in polyamides specify the methods for calculating the viscosity number of nylon resins using dilute acid solutions. The ISO 307 standard is the international benchmark for determining the molecular weight and processing characteristics of nylon 6 and nylon 66. It provides a consistent procedure for dissolving the polymer in a solvent and measuring the time it takes for the solution to flow through a glass capillary tube.
This measurement is used by both polymer producers and fiber spinners to ensure the material is suitable for extrusion. Compliance with this standard allows for the global trade of nylon resins with guaranteed performance specifications.
Dissolution Procedure
Accuracy of the viscosity measurement depends on the careful preparation of the polymer solution according to the exact parameters of the test. Under ISO 307, a specific mass of nylon is dissolved in a solvent such as formic acid, sulfuric acid, or m cresol at a controlled temperature. The choice of solvent depends on the type of polyamide being tested and the expected range of the viscosity number.
Technicians must ensure that the polymer is completely dissolved and that the solution is free from air bubbles or undissolved particles. This liquid is then passed through a viscometer where the flow time is recorded with high precision. Small variations in the concentration of the solution or the temperature of the room can lead to inaccurate results.
Viscosity Metric
Resulting flow time is compared against the flow time of the pure solvent to calculate the relative viscosity of the polymer. ISO 307 uses this value to determine the viscosity number, which is a direct indicator of the average length of the polymer chains. A higher viscosity number indicates a higher molecular weight, which translates to better mechanical properties in the finished fiber.
Spinners use this data to set the temperature and pressure of their extrusion lines. If the viscosity is too low, the fiber will be weak and prone to breakage. If it is too high, the melt will not flow properly through the spinneret holes.
This metric is the primary tool for maintaining consistency across different batches of raw material.
Industrial Standard
Global supply chains for synthetic textiles rely on standardized testing to ensure that materials from different suppliers can be used interchangeably. ISO 307 provides a common language for quality control that is understood by chemists and engineers in every part of the world. Mills often include a specific viscosity range in their purchase contracts to protect against variations in the feedstock.
Regular testing according to this standard helps identify degradation of the polymer during storage or transport. It also allows for the comparison of virgin and recycled nylon resins to ensure that recycled content does not compromise the quality of the final product. As the industry moves toward more complex material blends, the role of standardized molecular testing becomes even more important.
Final verification of a nylon shipment is not complete without an ISO 307 test report.
