Thickening effect of hydroxypropyl methylcellulose

First of all

Hydroxypropyl methylcellulose imparts excellent stickiness to wet mortar. It can significantly increase the adhesion of wet mortar to the base layer and improve the sag resistance of the mortar.

It is widely used in plastering mortar, exterior wall thermal insulation system and facing brick bonding mortar. The thickening effect of cellulose ether can also increase the homogeneity and dispersion resistance of fresh cement-based materials.

Prevents delamination, segregation and bleeding of mortar and concrete, and can be used in fiber concrete, underwater concrete and self-compacting concrete.

second

Hydroxypropyl methylcellulose increases the viscosity of cement-based materials due to the viscosity of the cellulose ether solution. The index of “viscosity” is usually used to evaluate the viscosity of the cellulose ether solution. The viscosity of the cellulose ether generally refers to the cellulose ether solution with a certain concentration (such as 2%).

At the specified temperature (such as 20 ° C) and shear rate (or rotation rate, such as 20 rpm). Viscosity value measured with a specified measuring instrument (such as a rotational viscometer).

Viscosity is an important parameter for evaluating the performance of cellulose ethers. The higher the viscosity of the hydroxypropyl methylcellulose solution, the better the viscosity of the cement-based material. The adhesion to the substrate is also good, the stronger the anti-sag and anti-dispersion capabilities.

However, if its viscosity is too large, it will affect the fluidity and operability of the cement-based material (such as sticking a plastering knife during the construction of plastering mortar). Therefore, the viscosity of cellulose ether used in dry-mixed mortar is usually 15,000 ~ 60,000 mPa. S-1. Self-levelling mortars and self-compacting concretes that require high fluidity require lower viscosity of cellulose ether.

In addition, the thickening effect of hydroxypropyl methylcellulose will increase the water demand of cement-based materials, thereby increasing the yield of mortar.

The viscosity of the hydroxypropyl methylcellulose solution depends on the following factors:

1

Molecular weight (or degree of polymerization) and concentration of cellulose ether, solution temperature, shear rate, and test method.

2

The higher the degree of polymerization of the cellulose ether, the larger the molecular weight. The higher the viscosity of its aqueous solution;

3

The higher the amount (or concentration) of cellulose ether, the higher the viscosity of its aqueous solution. However, care should be taken when selecting the appropriate blending amount. So as not to add too much, affecting the performance of mortar and concrete;

4

As with most liquids, the viscosity of cellulose ether solutions decreases with increasing temperature. And the higher the cellulose ether concentration, the greater the effect of temperature;

5

The cellulose ether solution is usually a pseudoplastic body and has a shear thinning property. The greater the shear rate during the test, the lower the viscosity.

Therefore, the cohesiveness of the mortar will be reduced due to the external force, which is conducive to the scraping construction of the mortar. So that the mortar can have good workability and cohesiveness.

However, cellulose ether solutions exhibit Newtonian fluid characteristics at very low concentrations and low viscosities.

As the concentration increases, the solution gradually exhibits pseudoplastic fluid properties. And the higher the concentration, the more obvious the pseudoplasticity.