Viscosity detection by HPMC

How to test the viscosity of hydroxypropyl methylcellulose HPMC

Let’s first talk about how hydroxypropyl methylcellulose (hpmc) detects its viscosity. The viscosity mentioned here refers to the apparent viscosity, which is an important indicator of HPMC. Rotational viscometers are now commonly used to measure the viscosity. In China, NDJ-1 and NDJ-4 viscometers are generally used, and the formula is η=Kα. η represents the viscosity, and the unit is also mPa.s, K is the coefficient of the viscometer, and α is the reading of the viscometer pointer.

The detection method of 2% viscosity of hydroxypropyl methylcellulose:
1. This method is suitable for determining the dynamic viscosity of non-Newtonian fluids (solutions, suspensions, emulsion dispersion liquids or surfactant solutions, etc.) of high polymers.
2. Instruments and Utensils
2.1 Rotational viscometer (the Chinese Pharmacopoeia stipulates the use of NDJ-1 and NDJ-4 types)
2.2 Constant temperature water bath constant temperature accuracy error 0.1 ℃
2.3 Thermometer graduation 20℃
2.4 Frequency meter The viscometer (such as NDJ-1 type, NDJ-4 type) with frequency stabilization measures should be used as a backup. Accuracy 1%a
3. Operation method
Accurately weigh 8.0g of the sample, put it into a dry, tared 400mL tall beaker, add about 100mL of 80-90℃ hot water, stir for 10min to disperse evenly, add cold water to a total of 400mL while stirring. At the same time, stir continuously for about 30 minutes to make it into a 2% (w/w) solution, put it in the refrigerator to cool in an ice bath until the surface is thinly iced, take it out and put it in a constant temperature tank to keep the center temperature at 20°C.
3.1 The installation and operation of the instrument shall be carried out according to the instruction manual of the instrument, and the appropriate rotor and rotational speed shall be selected according to the viscosity range of the test product and the provisions of the Pharmacopoeia under the main text of the product.
3.2 Determination of the viscosity of hydroxypropyl methylcellulose. The sample is 2% aqueous solution at 20°C.
3.3 Take the sample to be tested and put it in the container specified by the instrument. After constant temperature for 30 minutes, measure the deflection angle (a) according to the law. Turn off the motor, and then turn it on again to make a measurement. The difference between each measured value and the average value shall not exceed ±3% of the average value, otherwise a third measurement should be made.
3.4 Take the average value of 2 measurements and calculate according to the formula to get the dynamic viscosity of the test product.
4. Record and calculation
4. 1 Record the type of rotary viscometer, the number and rotation speed of the rotor used, the constant of the viscometer ((K’ value), the measured temperature, and the value measured each time.
4.2 Calculation formula
Dynamic viscosity (MPa”s)=Ka where K is the viscometer constant a measured with a standard liquid of known viscosity is the deflection angle

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