The Way to Measure the Viscosity of Hydroxypropyl Methylcellulose HPMC

The Way to Measure the Viscosity of Hydroxypropyl Methylcellulose HPMC

In order to obtain accurate and reliable hydroxypropyl methylcellulose viscosity measurement data, several points must be noted:

1. The performance indicators of the instrument must meet the requirements of the national metrological verification regulations.

The instruments used in the viscosity measurement of hydroxypropyl methylcellulose should be checked periodically, and if necessary (the instrument is frequently used or in a critical state of being qualified), an intermediate self-examination should be carried out to confirm that its measurement performance is qualified, and the coefficient error is within the allowable range, otherwise Accurate data could not be obtained.

2, Pay special attention to the temperature of the liquid to be measured.

Many users ignore this point and think that the temperature difference does not matter. Our experiments have proved that when the temperature deviation is 0.5 °C, the viscosity value deviation of some liquids exceeds 5%, and the temperature deviation has a great influence on the viscosity. The temperature increases and the viscosity decreases. Therefore, special attention should be paid to keep the temperature of the liquid to be measured constant around the specified temperature point, and it is best not to exceed 0.1 °C for accurate measurement.

3. The selection of measuring container (outer cylinder).

For the double-cylinder rotational viscometer, read the instrument manual carefully, and different rotors (inner cylinders) match the corresponding outer cylinders, otherwise the measurement results will deviate greatly. For a single-cylinder rotational viscometer, in principle, the radius of the outer cylinder is required to be infinite. In actual measurement, the inner diameter of the outer cylinder, that is, the measuring container, is required to be no less than a certain size. For example, the NDJ-1 rotational viscometer requires a beaker or a straight cylindrical container with a diameter of not less than 70mm. Experiments have shown that especially when the No. 1 rotor is used, if the inner diameter of the container is too small, a large measurement error will be caused.

4. Correctly select the rotor or adjust the speed so that the displayed value is between 20 and 90 grids.

This type of hpmc instrument adopts the dial and pointer method for reading, and its stability and reading deviation are combined with 0.5 grids. If the reading is too small, such as around 5 grids, the relative error caused is more than 10%. If the reading is at 50 grids, the relative error can be reduced to 1%. If the indicated value is above 90 grids, the torque generated by the hairspring will be too large, which will easily cause creep and damage the hairspring, so the rotor and speed must be correctly selected.

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