Plastics - Determination of the viscosity of polymers in dilute solution using capillary viscometers - Part 1: General principles
1Key Takeaways
This document defines the general conditions for the determination of the reduced viscosity, intrinsic viscosity and K-value of organic polymers in dilute solution. It defines the standard parameters that are applied to viscosity measurement. This document is used to develop standards for measuring the viscosities in s…
2Expert Interpretation
An in-depth interpretation of the ISO 1628-1:2021 standard's technical specifications for determining the viscosity of dilute polymer solutions using a capillary viscometer, including test principles, instrument selection, solution preparation, data processing methods, and error source analysis, which is applicable to polymer material research and development and quality control.
Analysis of the core content of the standard
ISO 1628-1:2021 fourth edition specifies a general method for determining the reduced viscosity, intrinsic viscosity and K value of dilute organic polymer solutions using a capillary viscometer. The standard is applicable to the viscosity measurement of polymer solutions for which no separate standard has been established.
Definition of Key Terms
| Term | Definition | Unit |
|---|---|---|
| Relative Viscosity (ηr) | The ratio of the viscosity of a solution to the viscosity of the pure solvent | Dimensionless |
| Reduced Viscosity (I) | The ratio of the relative viscosity increment to the concentration | cm³/g |
| Intrinsic Viscosity [η] | The reduced viscosity limit at infinite dilution | cm³/g |
Test principles and technical points
The effluent time ratio (t/t0) of solution and solvent is measured by Ubbelohde viscometer. The kinetic energy correction can be ignored when the following conditions are met:
- Difference between solvent density and solution density <0.5%
- Kinetic energy correction amount <3% of solvent viscosity
Important parameter control: The solution concentration should keep the t/t0 ratio between 1.2-2.0. The recommended test temperature is 25±0.05℃.
Instrument Selection Specifications
The standard recommends the use of Ubbelohde type suspension level viscometer, and the capillary size should be selected according to the solvent kinematic viscosity as shown in Table 1:
| Solvent kinematic viscosity (mm²/s) | Recommended viscometer model | Capillary inner diameter (mm) |
|---|---|---|
| 0.15-0.30 | 0C | 0.36 |
| 0.51-0.75 | 0B | 0.46 |
| 2.51-5.00 | 1B | 0.84 |
Key steps of the test process
- Solution preparation:Ensure complete dissolution without microgel and precise concentration control
- Viscometer cleaning:Need to use chromic acid cleaning solution (pay attention to safety protection)
- Constant temperature control:Bath temperature fluctuation ≤0.05K
- Outflow time measurement:The deviation between two consecutive measurements must be ≤0.25%
Error sources and quality control
The main error sources include:
- Kinetic energy correction error:Control by selecting appropriate capillary size
- Shear effect: Special attention should be paid when the intrinsic viscosity is >500cm³/g
- Temperature fluctuation: Precision temperature control equipment should be used
The standard requires that the solvent outflow time should be between 70-200 seconds to ensure measurement accuracy.
Major changes in the new edition
Major updates compared to the fourth edition (2009):
- Deleted references to the obsolete ISO 3205 standard
- Revised chart annotation specifications
- Added nominal values of viscometer constants in Table 1
Implementation recommendations
1. Method validation:Confirm the concentration-viscosity linear relationship for new polymer systems
2. Equipment calibration:Regularly calibrate the viscometer constant with standard oil
3. Data report:Must include key information such as test temperature, solvent type, instrument model, etc.
4. Safety precautions:Protective equipment is required when using chromic acid for cleaning