What factors affect the viscosity of hydroxypropyl methylcellulose

Hydroxypropyl methylcellulose HPMC has good thickening properties for the application of wet mortar, which can significantly increase the bonding ability between the wet mortar and the base layer, and can also improve the anti-sag performance of the mortar, so it is widely used In plastering mortar, external wall insulation system and facing brick bonding mortar. For the thickening effect of cellulose ether, it can also increase the homogeneity and resistance to dispersion of fresh cement-based materials, and can also prevent the delamination, segregation and bleeding problems of mortar and concrete. It can be used in In fiber concrete, underwater concrete and self-compacting concrete.

Hydroxypropyl methylcellulose HPMC can increase the viscosity performance of cement-based materials. This performance mainly comes from the viscosity of cellulose ether solution. Generally, the numerical index of viscosity is used to judge the viscosity of cellulose ether solution, while fiber The viscosity of cellulose ether usually mainly refers to a certain concentration of cellulose ether solution, usually 2%, measured at a specified temperature, such as 20 degrees and a rotation rate, using a specified measuring instrument, such as a rotational viscometer. viscosity value. Viscosity is one of the important parameters for evaluating the performance of cellulose ether. The higher the viscosity of the hydroxypropyl methylcellulose solution, the better the viscosity of the cement-based material, the better the adhesion performance to the substrate, and at the same time it has The ability to resist sagging and dispersion will be stronger, but if its viscosity is too high, it will affect the flow performance and operability of cement-based materials. For example, plastering mortar may stick to the plastering knife during construction operations. Therefore, 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 that require higher flow properties, the viscosity of cellulose ether is required to be relatively higher. Low. In addition to this, the thickening effect of hydroxypropyl methylcellulose also increases the water demand of cement-based materials, thereby increasing mortar yields.

Hydroxypropyl methylcellulose HPMC

What factors affect the viscosity of hydroxypropyl methylcellulose? Mainly depends on the following reasons:
 
1. If the polymerization degree of cellulose ether of hydroxypropyl methylcellulose is higher, its molecular weight will be larger, resulting in a higher viscosity of its aqueous solution.
 
2. If the blending amount or concentration of cellulose ether is higher, the viscosity of the aqueous solution will be higher. However, attention should be paid to selecting the appropriate blending amount when using it, mainly to avoid excessive blending. It will affect the working performance of mortar and concrete.
 
3. Hydroxypropyl methylcellulose cellulose ether, like most liquids, the viscosity of the cellulose ether solution will decrease as the temperature increases, and the higher the concentration of the cellulose ether, the lower the temperature will be. The impact will be greater.
 
4. Cellulose ether solutions are usually pseudoplastic and have shear thinning characteristics. The greater the shear rate during testing, the smaller the viscosity.
 
To sum up, the cohesion of mortar will be reduced due to the action of external force, which is also conducive to the scraping construction operation of mortar, resulting in the mortar having good cohesion and workability at the same time. However, cellulose ether If the solution has a low concentration and low viscosity, it will exhibit the characteristics of a Newtonian fluid. When the concentration increases, the solution will gradually exhibit the characteristics of a pseudoplastic fluid. And if the concentration is higher, the pseudoplasticity will become more obvious.