What are the factors affecting the viscosity of hydroxypropyl methylcellulose?
Hydroxypropyl methylcellulose HPMC has good thickening characteristics for the application of wet mortar, can significantly increase the bonding ability between wet mortar and base course, and can also improve the anti sag performance of mortar. Therefore, it is widely used in plastering mortar, external wall external insulation system and brick bonding mortar. For the thickening effect of cellulose ether, it can also increase the uniformity and anti dispersion ability of fresh cement-based materials, and prevent the problems of delamination, segregation and bleeding of mortar and concrete. It can be applied to fiber concrete, underwater concrete and self compacting concrete.
Hydroxypropyl methylcellulose HPMC can increase the viscosity of cement-based materials. This performance mainly comes from the viscosity of cellulose ether solution. Generally, the viscosity of cellulose ether solution is judged by the numerical index of viscosity, and the viscosity of cellulose ether usually mainly refers to a certain concentration of cellulose ether solution, usually 2%, at the specified temperature, For example, at 20 degrees and under the condition of rotation rate, use the viscosity value measured by the specified measuring instrument, such as rotary viscometer. Viscosity is one of the important parameters to judge the performance of cellulose ether. The higher the viscosity of hydroxypropyl methylcellulose solution, the better the viscosity of cement-based materials, the better the adhesion to the substrate, and the stronger the anti sag ability and anti dispersion ability. However, if its viscosity is too large, it will affect the fluidity and operability of cement-based materials, For example, the plastering knife is stuck to the plastering mortar during construction, so the viscosity of cellulose used in dry mixed mortar is usually 15000-60000mpa S-1, relatively speaking, for self leveling mortar and self compacting concrete requiring high fluidity, the viscosity of cellulose ether is required to be relatively lower. In addition, the thickening effect of hydroxypropyl methylcellulose will also increase the water demand of cement-based materials, so as to improve the output of mortar.
What factors affect the viscosity of hydroxypropyl methylcellulose? It mainly depends on the following reasons:
1. The higher the degree of polymerization of cellulose ether of hydroxypropyl methylcellulose, the greater its molecular weight and the higher the viscosity of its aqueous solution.
2. The higher the amount or concentration of cellulose ether, the higher the viscosity of its aqueous solution. However, attention should be paid to selecting the appropriate amount in use, mainly to avoid that if the amount is too high, it will affect the working performance of mortar and concrete.
3. Like most liquids, the viscosity of cellulose ether solution will decrease with the increase of temperature, and the higher the concentration of cellulose ether, the greater the effect of temperature.
4. Cellulose ether solution is usually pseudoplastic, which has the characteristics of shear thinning. The greater the shear rate, the smaller the viscosity.
In conclusion, the cohesion of mortar will be reduced due to the action of external force, which is also conducive to the scraping construction of mortar, resulting in good cohesion and constructability of mortar at the same time. However, if the concentration of cellulose ether solution is low and the viscosity is small, it will show the characteristics of Newtonian fluid. When the concentration increases, The solution slowly presents the characteristics of pseudoplastic fluid, and the higher the concentration, the more obvious the pseudoplasticity.