Water retention of cellulose ether in mortar.

Cellulose ether is widely used in building materials, among which water retention in mortar is one of its important functions. Water retention refers to the ability of a material to retain water after absorbing water, which has a vital impact on the performance of mortar. This article will discuss in detail the water retention of cellulose ether in mortar, including its mechanism of action, influencing factors, experimental data and practical applications.

## 1. Basic properties of cellulose ether

### 1.1 Chemical structure

Cellulose ether is a class of polymer compounds obtained by chemical modification of natural cellulose. Its basic structural unit is β-D-glucose, which is connected by 1,4-glycosidic bonds to form long chains. The modification of cellulose ether mainly includes methylation, hydroxypropylation, etc., which makes it have good solubility and film-forming properties.

### 1.2 Main types

Common types of cellulose ethers include:

- **Hydroxypropyl methylcellulose (HPMC)**: It has good water retention and thickening properties and is widely used in building mortar.

- **Methyl cellulose (MC)**: has high water retention and film-forming properties, and is often used in dry-mixed mortar.

- **Carboxymethyl cellulose (CMC)**: has good thickening and water retention properties, and is mainly used in cement-based materials.

## 2. Water retention mechanism of cellulose ether in mortar

### 2.1 Prolongation of hydration reaction

The cement in the mortar requires a certain amount of water during the hydration process. Cellulose ether reduces the evaporation of water in the mortar through its water retention effect, prolongs the hydration reaction time of the cement, makes the cement fully hydrated, forms a dense hydration product, and improves the strength and adhesion of the mortar.

### 2.2 Reduce capillary action

The polymer network structure formed by cellulose ether in the mortar can prevent the loss of water along the capillary channel and reduce the capillary action inside the mortar. This mechanism enables the mortar to maintain a high water content in a high temperature or dry environment, preventing cracking and strength loss caused by premature drying.

### 2.3 Increase viscosity and fluidity

Cellulose ether can significantly increase the viscosity and fluidity of mortar, forming a uniform and stable mixture. This uniformity makes the water distribution more uniform, avoiding the concentration or local loss of water in the mortar, thereby improving the overall water retention.

## 3. Factors affecting the water retention of cellulose ether in mortar

### 3.1 Degree of etherification

The degree of substitution (DS) of cellulose ether refers to the number of hydroxyl groups substituted in the cellulose molecule. The higher the degree of etherification, the better the hydrophilicity and solubility of cellulose ether, and thus the stronger its water retention. Generally speaking, a moderate degree of etherification can provide the best water retention effect.

### 3.2 Molecular weight

The molecular weight of cellulose ether also has an important influence on its water retention. Cellulose ethers with larger molecular weights have higher solutions in water and can better retain water. However, too high a molecular weight may cause difficulty in dissolution, thus affecting its actual application effect.

### 3.3 Temperature

Temperature has a significant effect on the water retention of cellulose ether. Generally speaking, cellulose ether has better water retention in low temperature environment, but its water retention will decrease in high temperature environment. This is because under high temperature conditions, water evaporation is accelerated, and the water retention effect of cellulose ether is challenged.

### 3.4 Addition amount

The amount of cellulose ether added to mortar has a direct impact on its water retention. An appropriate amount of cellulose ether can significantly improve the water retention of mortar, but excessive addition may cause the mortar viscosity to be too high, affecting the construction performance. Therefore, the amount of cellulose ether added needs to be adjusted according to specific application requirements.

## 4. Experimental data and analysis

### 4.1 Experimental design

By adding different types and contents of cellulose ether to the standard mortar formula, its water retention performance is tested. The experiment mainly includes the following steps:

1. Prepare standard mortar samples.

2. Add different types and contents of cellulose ether respectively.

3. Evaluate the water retention and mechanical properties of mortar through water retention test and compressive strength test.

### 4.2 Experimental results

The experimental results show that the type, degree of etherification and addition amount of cellulose ether have a significant effect on the water retention of mortar. Taking HPMC as an example, when the degree of etherification is 1.2-1.5, the water retention rate of mortar reaches the best state, about 95%. At the same time, when the addition amount is 0.1%-0.3%, the water retention and construction performance of mortar are both good.

### 4.3 Data analysis

The following conclusions can be drawn from the analysis of experimental data:

- When the degree of etherification is moderate, the water retention of cellulose ether is the best.

- When the molecular weight is large, the water retention of cellulose ether is better, but it needs to be controlled within an appropriate range.

- The increase in temperature will reduce the water retention of cellulose ether, so cooling measures need to be taken when constructing in a high temperature environment.

- The appropriate addition of cellulose ether can significantly improve the water retention and mechanical properties of mortar, but excessive addition will affect the construction performance.

## 5. Practical application of cellulose ether in mortar

### 5.1 Wall plaster mortar

In wall plaster mortar, the water retention of cellulose ether can prevent the mortar from losing water too quickly during the plastering process, avoid cracking and strength reduction, and ensure the flatness and adhesion of the plaster layer.

### 5.2 Tile bonding mortar

In tile bonding mortar, the water retention of cellulose ether helps to extend the open time and adjustment time of the mortar, improve the firmness of tile bonding and construction efficiency.

### 5.3 Self-leveling mortar

In self-leveling mortar, the water retention of cellulose ether can maintain the fluidity and uniformity of the mortar, ensure the flatness and wear resistance of the self-leveling layer.

### 5.4 Repair mortar

In repair mortar, the water retention of cellulose ether can improve the adhesion and crack resistance of the mortar and extend the service life of the repair layer.

## 6. Conclusion

In summary, the water retention of cellulose ether in mortar is one of its key properties, which directly affects the construction performance and final quality of mortar. By rationally selecting the type, degree of etherification, molecular weight and addition amount of cellulose ether, the water retention and mechanical properties of mortar can be significantly improved. In practical applications, it is necessary to adjust the use parameters of cellulose ether according to the specific construction environment and requirements to maximize its water retention effect and ensure the quality and durability of building materials. In the future, with the continuous development of cellulose ether technology, its application in mortar water retention will be more extensive and in-depth, promoting the innovation and progress of building materials technology.