hpmc chemical-How to test the viscosity of hydroxypropyl methylcellulose
Let’s first talk about how hydroxypropyl methylcellulose detects its viscosity. The viscosity mentioned here refers to the apparent viscosity, which is an important index of hydroxypropyl methylcellulose.
mark. The usual measurement methods are rotational viscometry, capillary viscometry and fall viscometry. The previous method for the determination of hydroxypropyl methylcellulose was capillary viscosity.
The Ubbelohde viscometer was used for the measurement method. Usually the measurement solution is a 2% aqueous solution, and the formula is: V=Kdt. V is the viscosity in mPa.s, K is the constant of the viscometer
, d represents the density at constant temperature, t refers to the time from top to bottom through the viscometer, the unit is s. This method is more complicated to operate, if there are insoluble substances
It is easy to cause errors, and it is difficult to identify the quality of hydroxypropyl methylcellulose. At present, a rotational viscometer is generally used to measure its viscosity.
NDJ-1 type viscometer, its 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 pointer of the viscometer.
Test method for 2% viscosity of hydroxypropyl methylcellulose:
1. This method is suitable for measuring the dynamic viscosity of non-Newtonian fluids (solutions, suspensions, emulsion dispersions, or surfactant solutions, etc.)
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 ± 0.10C
2.3 The temperature of the thermometer is 0.20C, which is checked periodically.
2.4 Frequency meter Viscometers (such as NDJ-1 and NDJ-4) that use frequency stabilization measures must be spared. Accuracy 1%a
3. Operation method Accurately weigh 8.0 g of the sample, put it into a dry, tared 400 mL high-footed beaker, add about 100 mL of 80-90 ℃ hot water, and stir for 10 minutes to make the solution.
Disperse evenly, add cold water to a total of 400mL while stirring. At the same time, keep stirring for about 30min to make a 2% (w/w) solution, put it in the refrigerator and cool it in an ice bath until the surface forms thin ice,
Take it out and put it into a constant temperature bath to keep the central temperature constant to 20±0.1 degrees to check the temperature.
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 rotor 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.
Rotating speed.
3.2 Adjust the temperature of constant temperature water according to the measurement under each drug item.
3.3 Take the test sample and place it in the container specified by the instrument, and after constant temperature for 30 minutes, measure the deflection angle (a) according to law. Turn off the motor, turn it on again to measure once, each time the measured value is the same as the level
The difference between the mean values shall not exceed 3% of the mean value, otherwise a third measurement shall be made.
3.4 Calculate the average value of 2 measurements according to the formula to obtain the dynamic viscosity of the test product.
4. Record and calculate
4.1 Record the model of the rotational viscometer, the rotor number and speed used, the viscometer constant ((K’ value), the measured temperature, and the measured value each time.
4.2 Calculation formula
Dynamic viscosity (MPa”s) = Ka where K is the viscometer constant measured with a standard liquid of known viscosity a is the deflection angle
