It is well known that hydroxypropyl methyl cellulose (HPMC) has a good thickening effect. HPMC increases the viscosity of cement-based materials from the viscosity of the HPMC solution. The “viscosity” index is usually used to evaluate the viscosity of HPMC solutions. Among them, the viscosity of HPMC generally refers to a certain concentration (such as 2%) of HPMC solution. The viscosity value measured with a specified measuring instrument (such as a rotational viscometer) under the specified temperature (such as 20°C) and shear rate (or rotation rate, such as 20 rpm).
Viscosity is an important parameter to evaluate the performance of MelaColl™ hydroxypropyl methylcellulose (HPMC). The higher the solution viscosity and the higher the viscosity of the cement-based material, the more beneficial the adhesion performance of the substrate, and the stronger the anti-sagging and anti-dispersion ability. On the contrary, it will affect the fluidity and operability of cement-based materials (such as sticking a plaster knife during plastering mortar construction).
To obtain accurate and reliable MelaColl™ hydroxypropyl methylcellulose (HPMC) viscosity measurement data, the following points must be noted:
1. The performance indicators of the instrument must meet the requirements of the national metrological verification regulations.
Hydroxypropyl methylcellulose (HPMC) viscosity measurement instruments need to be periodically verified. When necessary (the instrument is used frequently or is in a critical state of qualification), an intermediate self-examination shall be carried out to determine that its measurement performance is qualified to ensure that the coefficient error is within the allowable range, otherwise accurate data cannot be obtained.
2. Pay special attention to the temperature of the liquid being measured.
Many users ignore and think that the temperature deviation does not matter. However, our experiments prove that: when the temperature deviation is 0.5℃, the viscosity value deviation of some liquids exceeds 5%, and the temperature deviation has a significant influence on the viscosity，that is, the temperature increases and the viscosity decreases. Therefore, users should pay special attention to keeping the temperature of the measured liquid constant near the specified temperature point, and the accurate measurement should not exceed 0.1°C.
3. Selection of measuring container (outer cylinder).
For the dual-cylinder rotational viscometer, read the instrument manual carefully, and different rotors (inner cylinder) should match the corresponding outer cylinder. Otherwise, the measurement results will have a huge deviation. For a single-cylinder rotary viscometer, in principle, the radius of the outer cylinder is required to be infinite. In the 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 straight cylindrical container with a diameter of not less than 70mm. Experiments have proved that primarily when the No. 1 rotor is used if the inner diameter of the container is too small, large measurement errors will occur.
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, and its stability and reading deviation are combined with having 0.5 divisions. If the reading is too small such as around 5 divisions, the relative error caused is more than 10%. If the appropriate rotor or speed is selected to make the reading at 50 divisions, 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 selected correctly.
Our hydroxypropyl methylcellulose (HPMC) products have a wide range of viscosity grades from 400 to 200000. We offer both standard and customized grades to meet customers’ desired levels of performance properties. Please feel free to CONTACT US for more information or a sample!