Simplified Viscosity Analysis Of Paste-Like Materials

Measuring the viscosity of creamy, pasty or heterogeneous material presents a challenge for rotational viscometers when using traditional smooth geometries such as coaxial cylinder, cone-plate, or simple disk spindles. Creams and pastes may be non-flowing, forming voids around the spindle, resulting in false low viscosity values. Heterogeneous materials may consist of a moderate viscosity liquid filled with deformable solid particles which migrate away from the spindle during rotation, resulting in a measurement of the liquid viscosity rather than that of the mixture as a whole. To overcome these problems, the Helipath Stand with T-bar spindles is commonly used to test highly viscous heterogeneous materials, gels, pastes, creams, putty and other non-flowing substances where traditional smooth geometries fail.

A typical Helipath test may gather over four hundred data points from start to finish. Viewing the data graphically and analyzing to come up with a final result requires the use of applications software. With the new generation rheometers, it’s possible to configure multi step tests and perform comprehensive data analysis directly from the touch screen interface of the instrument without the use of a PC (Figure 1).

HOW IT WORKS

The Helipath Stand is an accessory to rotational viscometers and rheometers that incorporates a wire spindle (T-bar) and verticle drive unit. This system produces a helical path for the spindle during the measurement (Figure 1 Insert). Helipath data traces progress from the initial viscosity – just as the spindle begins to drill down through the material - to a "plateau" region where the spindle is in the bulk of the sample. The system then reverses direction, and the measured torque - and calculated viscosity – continues to be recorded as the spindle rises up to the initial starting point. The "plateau" for both the downstroke and upstroke data is based on the depth of the material in the container and the fixed speed of the Helipath drive. In the past, recording, viewing and analyzing this data was done manually or required the use of application software and a PC. In most cases, a single viscosity number was desired for a simple QC/QA measurement.

Today, Helipath testing with the new generation of rheometers has been simplified with the ability to configure multi step tests and perform comprehensive data analysis directly from the full color graphical touch screen display of the instrument without the use of a PC. The interface allows for control of all instrument parameters as well as data analysis and management. All data points will be displayed graphically in real time on the touch screen display during the test. Measurement data includes the complete set of measurement results and calculated values along with the test protocol. There are several options available for viewing test data including averaging which can be used to provide a single viscosity number for a QC/QA measure.

RESULTS:

All measurement data can be saved to the instrument’s internal memory or to a USB flash drive. Results can be viewed graphically (Figure 1) and analyzed directly on the instrument’s display. The post test averaging option allows both the down and up plateau data to be averaged separately or together to give a single QC/QA number for viscosity. Two data sets can be shown on the graph simultaneously or compared side by side in table format. Security 21CFR, available in new generation rheometers, include controlled user access and complete data integrity for each test.

CONCLUSIONS:

Measuring, analyzing and reporting viscosity data for creamy, heterogeneous or pasty materials can be simplified with the use of a Helipath Stand, T-bar spindles and the new generation of rheometers. Using the touch screen interface to create a customized multi step test, taking advantage of short data collection intervals and specific end condition times for the downstroke and upstroke steps, ensures an efficient and productive method requiring no operator involvement during the actual test. The results are displayed graphically or in table format and can be analyzed to provide QC/QA with a single measure for viscosity without the use of a PC.

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