The “ASTM D2196-20 Standard Test Methods for Rheological Properties of Non-Newtonian Materials by Rotary Viscometer”, developed by the American Society for Testing and Materials (ASTM), describes test methods for determining the apparent viscosity, shear thinning, and thixotropic properties of non-Newtonian materials in a shear rate range of 0,1 s −1 to 50 s −1 , using a rotary viscometer operating in a fluid contained in a 600 mL low-form Griffin beaker.
Test method A consists of determining the apparent viscosity of coatings and related materials by measuring the torque on a spindle rotating at constant speed in a 600 mL low form Griffin beaker.
Test methods B and C consist of determining the shear thinning and thixotropic (time dependent) rheological properties of materials. The viscosities of these materials are determined at a series of prescribed speeds on a rotational viscometer with a spindle operating in a liquid contained in a 600 mL low form Griffin beaker. Agitation of the material is carefully controlled immediately prior to viscosity measurements.
Test method A is used to determine the apparent viscosity at a given rotational speed, but viscosities at two or more speeds provide a better characterization of a non-Newtonian material than a single viscosity measurement.
With test methods B and C, the degree of shear thinning is indicated by the decrease in viscosity with increasing rotational speed. The degree of thixotropy is indicated by comparing the viscosities at increasing and decreasing rotational speeds (test method B), the viscosity recovery (test method B), or the viscosities before and after high shear (combination of test methods B and C). The high shear in test method C approaches shear during paint application. The viscosity behavior measured after high shear is representative of the properties of the paint immediately after application.
The primary equipment used in these tests is the rotational viscometer. The basic instrument should have at least the following features:
The following equipment is also used in the tests:
When preparing the sample, a 0,5 L or 1 L container is filled with the sample to a 25 mm gap from the top of the sample and brought to 25 degrees plus/minus 0,5 degrees or another agreed temperature before testing. The sample is shaken vigorously for 10 minutes on a shaker or equivalent, removed from the shaker and left at 25 degrees for 60 minutes before testing. The test is started no later than 65 minutes after removing the container from the shaker. The sample is not removed from the container in which it was shaken. The shaking time may be reduced if necessary or as agreed between the purchaser and the manufacturer, but in any case it shall not be less than 3 minutes.
When using test method A, all measurements are made at 25 degrees plus/minus 0,5 degrees or other agreed temperature. The instrument is placed on an adjustable stand. The viscometer is lowered to a level that will immerse the spindle to the appropriate depth. The instrument is leveled. The selected spindle is bent, placed to one side of the center of the material surface, and the spindle is inserted into the instrument. When connecting the spindle to the viscometer, it is necessary to avoid excessive side pressure that could affect alignment. It is also necessary to avoid rotating the spindle so that the viscometer pointer touches the stoppers at each end of the scale. A spindle/speed combination is selected that will give a minimum reading of 10 percent of the scale, but preferably it should be in the middle or upper part of the scale. The speed and spindle to be used may differ from this by agreement between the user and the manufacturer. The viscometer is lowered until the dip mark on the spindle touches the sample. The viscometer level is adjusted if necessary. The vessel is moved slowly in a horizontal plane until the spindle is approximately in the center of the vessel. Spindle rotation is started. The rotation speed is adjusted so that torque readings are between 10 percent and 100 percent. The viscometer is allowed to run until the reading stabilizes. The torque and viscosity reading are recorded.
When using test method B, all viscosity (or torque) measurements are made at 25 degrees plus/minus 0,5 degrees or other agreed temperature. The instrument is set up and the spindle is attached as described above. The different rotational speeds to be used for the test are decided (a minimum of three speeds is recommended). The viscometer is set at the slowest rotational speed selected for the test. Spindle rotation is started and the reading is recorded after ten revolutions (or other agreed number of revolutions). A higher initial rotational speed may be used if agreed between the manufacturer and the user. The rotational speed is increased in steps and the reading is recorded after ten revolutions at each speed. After an observation is made at the highest speed, the rotational speed is reduced in steps to the slowest speed and the reading is recorded after ten revolutions (or equivalent time) at each speed. After the final reading is taken at the slowest speed, rotation is stopped and the sample is allowed to stand for an agreed rest period, usually 1 minute. At the end of the rest period, spindle rotation is started at the slowest speed and the reading is recorded after ten revolutions (or other agreed number of revolutions).
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