HPMC manufacturer-The effect of cellulose ether in cement mortar

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HPMC manufacturer-The effect of cellulose ether in cement mortar

In ready-mixed mortar, only a little cellulose ether can significantly improve the function of wet mortar. It can be seen that cellulose ether is a primary additive that affects the construction function of mortar. ”
The selection of different types, different viscosities, different particle sizes, different viscosity degrees and addition amounts of cellulose ethers also have different effects on the progress of dry powder mortar performance. At that time, many masonry and plastering mortars have poor water retention properties, and the water slurry will separate after standing for a few minutes, so it is very important to add cellulose ether to the cement mortar.

Let’s take a look at the specific effects of cellulose ether in cement mortar!

Cellulose ether – water retention

Water retention is an important function of methyl cellulose ether, and it is also a function that many domestic dry powder mortar manufacturers, especially those in the south with high temperature areas, attach importance to. In the production of building materials, especially dry mortar, cellulose ether plays an irreplaceable role, especially in the production of special mortar (modified mortar), it is an indispensable part.

The viscosity, dosage, ambient temperature and molecular structure of cellulose ether have a great influence on its water retention function. Under the same conditions, the higher the viscosity of cellulose ether, the better the water retention; the higher the dosage, the better the water retention. Generally, a small amount of cellulose ether can greatly improve the water retention rate of the mortar. When the ambient temperature increases, the water retention of cellulose ether generally decreases, but some modified cellulose ethers also have better water retention under high temperature conditions; fibers with a lower degree of substitution The water retention function of plain ether is better.

The hydroxyl group on the cellulose ether molecule and the oxygen atom on the ether bond will form a hydrogen bond with the water molecule, so that the free water becomes bound water, and then has a good water retention effect; the bond between the water molecule and the cellulose ether molecular chain The mutual dispersing effect enables water molecules to enter the interior of the cellulose ether macromolecular chain, and is strongly bound, and then forms free water, surrounds the water, and improves the water retention of the cement slurry; cellulose ether improves the fresh cement slurry. The rheological function of the bulk, the porous network structure and the osmotic pressure or the film-forming function of the cellulose ether prevent the dispersion of water.

Cellulose ethers – thickening and thixotropy

Cellulose ether endows the wet mortar with excellent viscosity, which can significantly increase the bonding ability between the wet mortar and the bottom layer, and improve the anti-sagging performance of the mortar. The thickening effect of cellulose ether can also increase the anti-scattering ability and homogeneity of freshly mixed materials, avoid material stratification, segregation and bleeding, and can be used in fiber concrete, underwater concrete and self-compacting concrete.

The thickening effect of cellulose ether on cement-based materials comes from the viscosity of the cellulose ether solution. Under the same conditions, the higher the viscosity of cellulose ether, the better the viscosity of the modified cement-based material, but if the viscosity is too large, it will affect the mobility and operability of the material (such as sticky plastering knife). Self-leveling mortar and self-compacting concrete that require high mobility require low viscosity of cellulose ether. In addition, the thickening effect of cellulose ether will also increase the water demand of cement-based materials and increase the output value of mortar.

High viscosity cellulose ether aqueous solution has high thixotropy, which is also a major characteristic of cellulose ether. Aqueous solutions of methylcellulose generally have pseudoplastic, non-thixotropic mobility below their gel temperature, but Newtonian mobility at low shear rates. Pseudoplasticity increases with the addition of cellulose ether molecular weight or concentration, regardless of the type and degree of substitution. Therefore, cellulose ethers of the same viscosity grade, whether it is MC, HPMC or HEMC, always exhibit the same rheological properties as long as the concentration and temperature remain stable. When the temperature increases, it forms a structural gel and exhibits high thixotropic activity.
Cellulose ethers with high concentration and low viscosity exhibit thixotropy even below the gel temperature. This property is of great benefit to the construction of building mortar to adjust its leveling and sagging. It needs to be clarified here that the higher the viscosity of the cellulose ether, the better the water retention, but the higher the viscosity, the higher the relative molecular weight of the cellulose ether, and the corresponding decrease in its solubility, which has a negative impact on the mortar concentration and construction performance.

Cellulose ether – air entrainment effect

Cellulose ethers have significant air-entraining effects on freshly mixed cement-based materials. Cellulose ether has together hydrophilic groups (hydroxyl, ether groups) and hydrophobic groups (methyl, glucose rings), is a surfactant, has surface activity, and then has an air-entraining effect. The air-entraining effect of cellulose ether will produce a “ball” effect, which can improve the working performance of the freshly mixed materials, such as adding the plasticity and smoothness of the mortar during the operation, which is conducive to the paving of the mortar; it will also increase the output value of the mortar. , reducing the cost of mortar production; but it will increase the porosity of the hardened material and reduce its mechanical properties such as strength and elastic modulus.

As a surfactant, cellulose ether also has a wetting or smoothing effect on cement particles, which increases the mobility of cement-based materials together with its air-entraining effect, but its thickening effect will reduce mobility. The effect of mobility is a generalization of plasticizing and thickening effects. Generally speaking, when the content of cellulose ether is very low, it is mainly manifested as plasticizing or water-reducing effect; when the content is high, the thickening effect of cellulose ether is rapidly added, and its air-entraining effect tends to be full. So it is manifested as thickening effect or adding water requirement.

Cellulose ether – retarding effect

Cellulose ether will extend the coagulation time of cement paste or mortar and delay the hydration kinetics of cement, which is beneficial to improve the workability time of freshly mixed materials, improve the time loss of mortar consistency and concrete slump, but may also Delay the construction progress.