Cellulose ether is a polymer compound synthesized from natural cellulose through etherification process, and is an excellent thickener and water retention agent.
Research Background
Cellulose ethers have been widely used in dry-mixed mortar in recent years, the most widely used are some non-ionic cellulose ethers, including methyl cellulose ether (MC), hydroxyethyl cellulose ether (HEC), hydroxyethyl cellulose ether Methyl cellulose ether (HEMC) and hydroxypropyl methyl cellulose ether (HPMC). At present, there are not many literatures on the measurement method of the viscosity of cellulose ether solution. In our country, only some standards and monographs stipulate the test method of the viscosity of cellulose ether solution.
The preparation method of cellulose ether solution
Preparation of Methyl Cellulose Ether Solution
Methyl cellulose ethers refer to cellulose ethers containing methyl groups in the molecule, such as MC, HEMC and HPMC. Due to the hydrophobicity of the methyl group, the cellulose ether solutions containing methyl groups have thermal gelation properties, that is, they are insoluble in hot water at a temperature higher than their gelation temperature (about 60-80°C). In order to prevent the cellulose ether solution from forming agglomerates, heat the water above its gel temperature, about 80~90°C, then add the cellulose ether powder into the hot water, stir to disperse, keep stirring and cool down To the set temperature, it can be prepared into a uniform cellulose ether solution.
Solubility properties of non-surface-treated methylcellulose-containing ethers
In order to avoid the agglomeration of cellulose ether during the dissolution process, manufacturers sometimes carry out chemical surface treatment on powdered cellulose ether products to delay dissolution. Its dissolution process occurs after the cellulose ether is completely dispersed, so it can be directly dispersed in cold water with a neutral pH value without forming agglomerates. The higher the pH value of the solution, the shorter the dissolution time of the cellulose ether with delayed dissolution properties. Adjust the pH value of the solution to a higher value. Alkalinity will eliminate the delayed solubility of the cellulose ether, causing the cellulose ether to form agglomerates when dissolving. Therefore, the pH value of the solution should be raised or lowered after the cellulose ether is completely dispersed.
Solubility properties of surface-treated methylcellulose-containing ethers
Preparation of Hydroxyethyl Cellulose Ether Solution
Hydroxyethyl cellulose ether (HEC) solution does not have the property of thermal gelation, therefore, HEC without surface treatment will also form agglomerates in hot water. Manufacturers generally carry out chemical surface treatment on powdered HEC to delay dissolution, so that it can be directly dispersed in cold water with a neutral pH value without forming agglomerates. Similarly, in a solution with a high alkalinity, HEC It can also form agglomerates due to delayed solubility loss. Since the cement slurry is alkaline after hydration and the pH value of the solution is between 12 and 13, the dissolution rate of the surface-treated cellulose ether in the cement slurry is also very fast.
Solubility properties of surface-treated HEC
Conclusion and Analysis
1. Dispersion process
In order to avoid adverse effects on the test time due to the slow dissolution of surface treatment substances, it is recommended to use hot water for preparation.
2. Cooling process
Cellulose ether solutions should be stirred and cooled at ambient temperature to reduce the cooling rate, which requires extended test times.
3. Stirring process
After the cellulose ether is added to the hot water, be sure to keep stirring. When the water temperature drops below the gel temperature, the cellulose ether will start to dissolve, and the solution will gradually become viscous. At this time, the stirring speed should be reduced. After the solution reaches a certain viscosity, it needs to stand still for more than 10 hours before the bubbles slowly float to the surface to burst and disappear.
Air Bubbles in Cellulose Ether Solution
4. Hydrating process
The quality of cellulose ether and water should be measured accurately, and try not to wait for the solution to reach a higher viscosity before replenishing water.
5. Viscosity test
Due to the thixotropy of cellulose ether solution, when testing its viscosity, when the rotor of the rotational viscometer is inserted into the solution, it will disturb the solution and affect the measurement results. Therefore, after the rotor is inserted into the solution, it should be allowed to stand for 5 min before testing.
Post time: Mar-22-2023