Introduction
ASTM D7395 is a method for the determination of a sample’s viscosity using a cone/plate configuration at a set shear rate of 500 s⁻¹. The system is verified using one to three certified calibration oils of known viscosity.
The NETZSCH Kinexus Prime series of rheometers can characterize a broad range of complex fluids and semi-solids due to its sensitivity, the capability of carrying out measurements on small sample volumes, modular geometries, and advanced software capabilities. Particularly, these rheometers possess an ultra-low friction air bearing which provides unmatched sensitivity across very low (0.001 s⁻¹) to very high (10,000 s⁻¹) shear rates. This makes it an ideal instrument not only for research and development purposes, but also standardizing tests within a quality environment and achieving method (even ASTM) specifications.
Additionally, the programable rSpace software allows users to create their own sequences for sample loading, measurement, and automatic analysis; or access over 200 pre-built sequences (which span 6 languages). To illustrate this, a sequence was programmed which encompasses the requirements for ASTM D7395. In a quality control setting, this sequence could then be locked to ensure consistent use between users or across testing facilities.
Sequence for ASTM D7395
For testing samples in accordance with ASTM D7395, a custom sequence was produced capable of determining the viscosity of each standard oil and/or sample. For the measurement, a 20 mm and 2° cone and plate configuration was used such that a low volume of only 80 µl was required per run. Once a sample is loaded, the system moves to the trim gap, rotates slowly at 10 s⁻¹ to ensure sample spreading, and then prompts the user to ensure the sample is properly trimmed. For consistency, a positive displacement pipette was used to ensure a set volume was always dispensed and therefore no manual trimming was required.
In following ASMT D7395, the trimmed sample is then equilibrated at 25°C for 1 minute. Once at the set temperature, the 500 s⁻¹ shear rate is applied, and the viscosity is reported to the user after 15 seconds. Finally, the user is prompted as to whether they want to run another sample or not.
Measuring Standard Oils and Samples
Three standard mineral oils were evaluated to show the accuracy of the method across a wide viscosity range. The results of the mineral oils RTM12, RTM22, and RTM32 (each measured in duplicate), are summarized in Table 1.
From Table 1, it can be seen that all three standard mineral oils viscosities were well within 5% relative error compared to the reported viscosity value. Additionally, between the reproducibility runs for each reference mineral oil there was less than 2% relative error, well within the 10% acceptable margin reported by the standard.
Table 1: Measured viscosity of three reference mineral oils following ASTM D7395
| Mineral Oil | Reference Viscosity at 35.00°C (cP) | Measured Viscosity (cP) | Error Compared to Reference (%) |
|---|---|---|---|
| RTM12 | 55.21 | 55.99 ± 0.04 | 1.4 ± 0.1 |
| RTM22 | 688.9 | 710.6 ± 3.1 | 3.1 ± 1.0 |
| RTM32 | 6009 | 6080 ± 9 | 1.2 ± 0.1 |
With the sequence for the ASTM established, various materials were tested (in duplicate for reproducibility) to determine their viscosity according to ASTM D7395, the results of which are summarized in Table 2. Each sample was selected as they undergo a shearing or spreading action upon their application. Even a complex sample such as honey mustard which contains particles of mustard seed was still shown to be reproducible but contrasts the tighter measurements of the hand lotion and hair gel specimens. Using this sequence as a standard operating practice in a manufacturing environment would be useful for standardization and ensuring product reproducibility.
Table 2: Measured vsicosity of three samples following ASTM D7395
| Sample | Measured Viscosity (cP) According to ASTM D7395 |
|---|---|
| Hand lotion | 263.5 ± 10.2 |
| Hair gel | 918.3 ± 18.4 |
| Honey mustard | 323.3 ± 23.5 |
Summary
The NETZSCH Kinexus Prime series of rheometers offers users both versatility and a high degree of customization when it comes to the characterization of complex fluids and semi-solids. The programable software allows users to access hundreds of pre-built programs or create their own. Herein, a custom test method was generated for the Kinexus to follow ASTM D7395 for viscosity determination at a set shear rate of 500 s⁻¹.
NGB · Application Note 434 · EN · 0426 · Technical specifications are subject to change.
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