English
创建于2024.10.17
Importance of MHEC
In pre mixed mortar, a small amount of cellulose ether can significantly improve the performance of wet mortar, indicating that cellulose ether is a major additive that affects the construction performance of mortar.
Choosing different varieties, viscosities, particle sizes, viscosity levels, and amounts of cellulose ether also has different effects on improving the performance of dry powder mortar. Currently, the water retention performance of many masonry and plastering mortars is not very good, and separation of the water slurry can occur after a few minutes of standing. Therefore, adding cellulose ether to cement mortar is quite important.
Let's take a detailed look at the functions of cellulose ether in cement mortar together!
1. Cellulose ether - water retention
Water retention is an important property of methyl cellulose ether, and it is also a concern for many dry mortar manufacturers in China, especially those in areas with higher temperatures in the south. Cellulose ether plays an irreplaceable role in the production of building materials, especially dry mortar, and is an indispensable and important component in the production of special mortar (modified mortar).
The viscosity, dosage, ambient temperature, and molecular structure of cellulose ether have a significant impact on its water retention performance. Under the same conditions, the higher the viscosity of cellulose ether, the better its water retention; The higher the dosage, the better the water retention. Usually, a small amount of cellulose ether can greatly improve the water retention rate of mortar. When the dosage reaches a certain level, the trend of increasing water retention rate slows down; As the ambient temperature increases, the water retention of cellulose ethers usually decreases, but some modified cellulose ethers also have good water retention under high temperature conditions; Cellulose ethers with lower degrees of substitution have better water retention performance.
The hydroxyl groups on cellulose ether molecules and the oxygen atoms on ether bonds will form hydrogen bonds with water molecules, turning free water into bound water and thus playing a good role in water retention; The mutual diffusion between water molecules and cellulose ether molecular chains allows water molecules to enter the interior of cellulose ether macromolecular chains and be strongly constrained, thereby forming free water, entangling water, and improving the water retention of cement slurry; Cellulose ether improves the rheological properties, porous network structure, and osmotic pressure of freshly mixed cement slurry, while its film-forming properties hinder water diffusion.
2. Cellulose ether - thickening and thixotropy
Cellulose ether endows wet mortar with excellent viscosity, significantly increasing the bonding ability between wet mortar and base layer, improving the anti sagging performance of mortar, and widely used in plastering mortar, brick bonding mortar, and exterior wall insulation systems. The thickening effect of cellulose ether can also increase the anti dispersion ability and homogeneity of newly mixed materials, prevent material layering, segregation, and bleeding, and can be used in fiber reinforced concrete, underwater concrete, and self compacting concrete.
The thickening effect of cellulose ether on cement-based materials comes from the viscosity of cellulose ether solution. Under the same conditions, the higher the viscosity of cellulose ether, the better the viscosity of modified cement-based materials. However, if the viscosity is too high, it will affect the flowability and operability of the material (such as using a plastering knife). Self leveling mortar and self compacting concrete with high liquidity requirements require low viscosity of cellulose ether. In addition, the thickening effect of cellulose ether will increase the water demand of cement-based materials and improve the yield of mortar.
High viscosity cellulose ether aqueous solutions have high thixotropy, which is also a major characteristic of cellulose ethers. The aqueous solution of methyl cellulose is usually pseudoplastic and non thixotropic below its gel temperature, but it is Newtonian at low shear rate. The pseudoplasticity increases with the increase of molecular weight or concentration of cellulose ether, regardless of the type and degree of substitution of substituents. So, cellulose ethers of the same viscosity grade, whether MC, HPMC, HEMC, as long as the concentration and temperature remain constant, always exhibit the same rheological properties. When the temperature increases, structural gel is formed and high thixotropic flow occurs.
Cellulose ether with high concentration and low viscosity shows thixotropy even below gel temperature. This property is highly beneficial for adjusting the leveling and sagging properties of building mortar during construction. It should be noted that the higher the viscosity of cellulose ether, the better its water retention, but the higher the viscosity, the higher the relative molecular weight of cellulose ether, and its solubility decreases accordingly, which has a negative impact on the concentration and construction performance of mortar.
3. Cellulose ether air entraining effect
Cellulose ether has a significant air entraining effect on freshly mixed cement-based materials. Cellulose ether has both hydrophilic groups (hydroxyl, ether groups) and hydrophobic groups (methyl, glucose ring), making it a surfactant with surface activity and thus having an air entraining effect. The air entraining effect of cellulose ether can produce a "rolling ball" effect, which can improve the workability of freshly mixed materials, such as increasing the plasticity and smoothness of mortar during operation, which is beneficial for the paving of mortar; It will also increase the output of mortar and reduce the production cost of mortar; But it will increase the porosity of the hardened material, reduce its mechanical properties such as strength and elastic modulus.
As a surfactant, cellulose ether also has a wetting or lubricating effect on cement particles, which, together with its air entraining effect, increases the fluidity of cement-based materials. However, its thickening effect also reduces fluidity. The effect of cellulose ether on the fluidity of cement-based materials is a combination of plasticizing and thickening effects. Generally speaking, when the content of cellulose ether is very low, it mainly exhibits plasticizing or water reducing effects; When the dosage is high, the thickening effect of cellulose ether rapidly increases, and its air entraining effect tends to saturate, so it manifests as thickening effect or increased water demand.
4. Cellulose ether - retarding effect
Cellulose ether can prolong the setting time of cement paste or mortar, delay the hydration kinetics of cement, which is beneficial for improving the workability of fresh materials, improving the loss of mortar consistency and concrete slump over time, but may also delay the construction progress.
Leave your information and we will contact you.
WhatsApp
Jean