ASTM D3236 Standard Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials
8. Procedure
8.1 Selection of Spindle - The measurement range of the rotational viscometer is determined by the dimensions of the spindle, the rotational speed, the size and shape of the container and the full scale range of the motor. From the estimated viscosity of the sample and the operations manual for the viscometer, select a spindle and rotational speed combination that will produce readings in the desired range.
NOTE 7 - Use only the spindle shown to be appropriate for the viscometer to be used.
8.1.1 Where more than one spindle is available for the range selected, choose the spindle that produces results nearest the midpoint of the measurable viscosity range. Viscometer torque scale readings shall be within the 10 % to 95 % range.
NOTE 8 - Care must be taken in the storage and handling of spindles and assemblies. Protect them from dust, corrosive deposits, and mechanical abuse. Avoid touching the calibrated section of the spindle with the hands. Clean the spindle and sample chamber thoroughly after each use. A recommended cleaning procedure is included in Annex A1.
8.2 Preparation of Sample - Using a fresh sample for each measurement, place the required amount of representative sample measured to the nearest 0.005 g (or 0.05 mL if handled in the molten state) in the specimen container. Melt the sample in an oven set at the desired test temperature or in the temperature bath preheated to the desired test temperature.
NOTE 9 - Avoid excessive or prolonged heating of the sample to minimize thermal and oxidative effects.
8.3 System Alignment and Spindle Insertion - After the sample is completely melted, lower the properly aligned and leveled viscometer spindle into the specimen container. Place the insulating cap over the specimen container.
8.4 Viscosity Determination:
8.4.1 Ensure that the material in the sample chamber is completely molten and that the test specimen is equilibrated to the selected temperature controller settings.
8.4.2 Initiate the spindle rotation at the lowest spindle speed available to minimize temperature gradients in the sample as well as possible shear effects.
8.4.3 When temperature equilibrium is indicated, stop the spindle rotation, remove the insulating cap, raise the viscometer and spindle, and inspect the liquid level on the spindle shaft. It should extend about 3 mm (1/8 in.) up the spindle shaft beyond the upper, tapered portion of the spindle. If the liquid level varies significantly from this, add or remove sample to provide this level.
8.4.4 Lower the spindle back into the test specimen. Replace the insulating cap. Initiate the spindle rotation at the lowest available speed, and allow the temperature equilibrium to be reestablished.
8.4.5 Continue spindle rotation for 15 min after apparent equilibrium.
8.4.6 Increase the spindle speed to that required to produce a scale reading nearest the midpoint of the scale, but in no case outside the 10-unit to 95-unit range. Record the scale reading.
8.4.7 After at least five additional revolutions of the spindle, record the second indicator reading.
8.4.8 Repeat 8.4.6 to until three consecutive scale readings are obtained that differ by no more than 0.5 unit.
9. Calculation
9.1 Determine the average of the three consecutive scale readings which differ by no more than 0.5 scale units from 8.4.7. Convert the indicatory reading to viscosity using the procedure described in the instrument instruction manual. Repeat this for each temperature.
NOTE 10 - If it is necessary to interpolate for viscosity values at intermediate temperatures, plot a series of observed apparent viscosity values on the logarithmic scale and the corresponding test temperatures on the linear scale of appropriate semi-logarithmic paper, using a series of at least three different temperatures. From the plot, determine the apparent viscosity at any temperature requested, within the range of test temperatures.
