Cellulose ether HPMC in mortar application technology

Cellulose ether HPMC in mortar application technology

The role of cellulose ether in mortar is water retention, increase cohesiveness, thickening, influence of condensation time, gas, because it has these characteristics, it has a wide range of application space in building materials mortar.

First, cellulose ether water retention is the most important property in the application of mortar.

The main factors affecting the water retention of cellulose ether are viscosity, particle size, dosage, active component, dissolution rate, water retention mechanism: the water retention of cellulose ether comes from the solubility and dehydration of cellulose ether itself. Although cellulose molecular chain contains a large number of hydroxyl groups with strong hydration performance, it is insoluble in water itself, because cellulose structure is highly crystalline, and the hydration capacity of hydroxyl group alone is not enough to destroy the strong intermolecular hydrogen bond and van der Waals force, so it only expands and does not dissolve in water. When the introduction of substituents in the molecular chain, not only the substitution group destroyed the hydrogen bond, but also because of the wedge between the adjacent chain substituents and the destruction of interchain hydrogen bond, the greater the substitution group pulled apart the greater the distance between molecules, the greater the destruction of hydrogen bond effect, cellulose lattice expanded, the solution into cellulose ether becomes water-soluble, the formation of high viscosity solution. As the temperature rises, the hydration of the polymer decreases and the water between the chains is driven out. When the dehydration is sufficient, the molecules begin to aggregate, forming a three-dimensional network of gel precipitation.

(1) cellulose ether particle size and mixing time on water retention

The water retention of mortar increases with the increase of viscosity of cellulose ether with the same dosage. The water retention rate of mortar increases with the increase of cellulose ether content and viscosity. When the content of cellulose ether exceeds 0.3%, the change of water retention of mortar tends to be balanced. The water retention capacity of mortar is largely controlled by the dissolution time. The dissolution of finer cellulose ether is faster, and the water retention performance is also faster.

(2) influence of degree of etherification and temperature of cellulose ether on water retention

As the temperature increases, the water retention decreases, and the higher the degree of etherification of cellulose ether, the better the water retention of cellulose ether at high temperature. In the process of use, the temperature of fresh mortar is usually lower than 35℃, under special climatic conditions, the temperature may reach or even exceed 40℃. In this case, it is necessary to adjust the formula, choose higher degree of etherification products, that is, consider the selection of appropriate cellulose ether.

Second ,The influence of cellulose ether on the gas content of mortar

In dry mixed mortar products, due to the addition of cellulose ether, the introduction of a certain amount of small, evenly distributed, stable bubbles in the new mixed mortar, due to the ball effect of bubbles, mortar has good construction, reduce the cracking and contraction of mortar, and improve the yield of mortar.

Three, cellulose ether effect on cement hydration

Cellulose ether has a delayed effect on the hydration of cement-based mortar, and the delayed effect increases with the increase of cellulose ether content. The influence factors of cellulose ether on cement hydration are: dosage, degree of etherification, cement type.