Effect of cellulose ethers on the rheological properties of gelling materials

Cellulose ether is a type of organic polymer compound widely used in construction cementitious materials. It has a significant impact on the rheological properties of cement-based, gypsum-based and other cementitious materials. The control of rheological properties is crucial to the construction performance, bonding performance and final mechanical properties of cementitious materials.

1. Types of cellulose ethers

Cellulose ethers mainly include methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), hydroxyethylmethylcellulose (HEMC), etc. Different types of cellulose ether molecular structures and their functional groups affect their solubility, thickening ability and rheological properties in cement-based and gypsum-based materials. Generally speaking, HPMC is the most widely used in the construction industry due to its high solubility and excellent thickening effect. HEMC is often used in building materials with higher requirements due to its good stability and low irritation.

2. Effect mechanism of cellulose ether on rheological properties

The main role of cellulose ethers in cementitious materials is to increase the viscosity of the slurry, thus affecting its rheological behavior. Its mechanism of action is mainly reflected in the following aspects:

(1) Thickening effect

Cellulose ether molecules form a network structure with flow resistance after being dissolved in water, thereby significantly increasing the viscosity of the slurry system. High viscosity slurry can effectively reduce water loss and improve water retention, which is especially important for materials that require a long construction time. In addition, the increased viscosity of the slurry can prevent the mortar from sagging and collapsing and enhance construction adaptability.

(2) Water retention effect

Cellulose ether has strong water retention properties and can form a water film on the surface of the slurry to slow down the evaporation rate of water. This characteristic can prevent the cement from losing too much water in the early stage, avoid cracking, and help the cement hydration reaction proceed evenly. In addition, cellulose ether can reduce the water-cement ratio, control the fluidity and consistency of the slurry, and further improve the water retention performance.

(3) Plasticity and thixotropy

The addition of cellulose ether can significantly improve the plasticity of the slurry, making it behave as a "thixotropic" fluid under the action of external force, that is, the fluidity is enhanced under the action of shear force, and the viscosity is restored after the external force is stopped. This property is very beneficial during application, as the slurry becomes easy to apply when applying and smoothing while maintaining good edge definition. Thixotropy allows the slurry to quickly recover its viscosity when left standing, thereby preventing sagging and improving construction efficiency and quality.

3. Effect of cellulose ethers on the rheological properties of different gelling materials

(1) Cement-based materials

In cement-based materials, the addition of cellulose ether can significantly increase the viscosity, improving the leveling and sag resistance during construction. Research shows that HPMC can significantly improve the plastic strength and viscosity of cement-based materials, and its effect depends on the molecular weight and addition amount of cellulose ether. In addition, the water retention of cellulose ether can prolong the hydration reaction time of cement, make early strength growth more uniform, and help improve the durability of the material.

(2) Gypsum-based materials

In gypsum-based materials, cellulose ethers can effectively improve the water retention and sag resistance of the material. Gypsum has rapid setting properties, so cellulose ethers are required to regulate the hydration rate and control water loss. Experiments show that gypsum-based materials added with cellulose ether have better workability and surface smoothness during construction, and show significant water retention effects especially in dry climates.

4. Influencing factors

The degree of influence of cellulose ether on the rheological properties of cementitious materials is affected by the type, molecular weight, addition amount and construction environment of cellulose ether. For example, higher molecular weight generally results in higher viscosity, but may reduce the workability of the material. Therefore, in practical applications, the type and dosage of cellulose ether need to be adjusted according to engineering requirements and environmental conditions. Especially under high temperature drying conditions, the addition amount of cellulose ether should be appropriately increased to maintain sufficient water retention and rheological properties.

5. Application examples

In building exterior wall coatings and plastering mortars, the application of cellulose ethers has achieved remarkable results. For example, adding an appropriate amount of HPMC to exterior wall plastering mortar can prevent the mortar from cracking, sliding and uneven application. Among ceramic tile adhesives, the thixotropic properties and water-retaining effect of cellulose ether can significantly improve the bonding force, making the ceramic tiles have better construction adaptability and bonding force on wet surfaces.

Cellulose ethers have a significant impact on the rheological properties of gelling materials. By adjusting the type and amount of cellulose ether, the thickening, water retention, thixotropy and other characteristics of the slurry can be effectively controlled, thereby optimizing construction performance and material quality. In practical applications, the reasonable selection of cellulose ethers according to different building needs and environmental conditions is of great significance to improving the construction effect and durability of building materials.