Matters needing attention when measuring hydroxypropyl methyl cellulose viscosity data

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 instrument in use for hydroxypropyl methyl cellulose viscosity measurement should be periodically verified. If necessary (the instrument is used frequently or is in a critical state of qualification), an intermediate self-check should be carried out to determine that its measurement performance is qualified, and the coefficient error is within the allowable range, otherwise Unable to obtain accurate data.

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

Many users ignore this point and think that the temperature difference does not matter. Our experiment proves that when the temperature deviation is 0.5℃, the viscosity value of some liquids deviates more than 5%, and the temperature deviation has a great influence on the viscosity. The temperature rises and the viscosity decreases. Therefore, special attention should be paid to keeping the temperature of the measured liquid constant near the specified temperature point, and it is best not to exceed 0.1°C for accurate measurement.

3, the choice of measuring container (outer cylinder).

For the dual-cylinder rotational viscometer, please read the instrument manual carefully. Different rotors (inner cylinder) match the corresponding outer cylinder, otherwise the measurement results will have a huge deviation. 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 not less than a certain size. For example, the NDJ-1 rotary viscometer requires a measuring beaker or a straight cylindrical container with a diameter of not less than 70mm. Experiments have proved that especially when using the No. 1 rotor, if the inner diameter of the container is too small, it will cause a larger measurement error.

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

This type of instrument uses a dial and pointer to read. Its stability and reading deviation are combined together to have 0.5 divisions. If the reading is too small, such as around 5 divisions, the relative error caused is more than 10%. If you choose a suitable rotor or speed to make If the reading is 50 divisions, the relative error can be reduced to 1%. If the display value is above 90 divisions, the torque generated by the hairspring will be too large, which will easily cause creep and damage the hairspring. Therefore, the rotor and speed must be selected correctly.

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