Cement products, such as concrete, mortar, and other building materials, are widely used in modern buildings. Cellulose ethers (such as hydroxypropyl methylcellulose (HPMC), hydroxyethyl methylcellulose (HEMC), etc.) are important additives that can significantly improve the performance of cement products. In order to achieve these excellent properties, it is crucial to master and control the performance of cellulose ethers.
1. Basic properties and functions of cellulose ethers
Cellulose ethers are a class of chemical derivatives of natural cellulose, in which the hydroxyl group is partially replaced by an ether group through an etherification reaction. Different types of cellulose ethers can be synthesized according to the type and number of substituents, and each type has a different role in cement products.
Viscosity of cellulose ethers:
The viscosity of cellulose ethers directly affects the rheology and stability of cement paste. High-viscosity cellulose ethers can improve the water retention and bonding strength of the paste, but may reduce its fluidity. Low-viscosity cellulose ethers help improve operability and fluidity.
Degree of substitution (DS) and molar substitution (MS):
The degree of substitution and molar substitution of cellulose ethers determine its solubility and the viscosity of the solution. High degree of substitution and high molar substitution can usually improve the water retention and stability of cellulose ethers.
Solubility of cellulose ethers:
The dissolution rate and solubility of cellulose ethers affect the uniformity of cement paste. Cellulose ethers with good solubility can form a uniform solution more quickly, thereby ensuring the uniformity and stability of the paste.
2. Choose suitable cellulose ethers
Different application scenarios have different performance requirements for cellulose ethers. Choosing the right type and specification of cellulose ether can significantly improve the performance of cement products:
Binders:
In applications such as tile adhesives and plaster mortars, high-viscosity cellulose ethers (such as HPMC) can provide better adhesion and lasting wettability, thereby improving construction performance and final bonding strength.
Water-retaining materials:
In self-leveling mortars and cement-based tile adhesives, cellulose ethers with high water retention (such as HEMC) are required. High water retention helps prevent premature water loss, thereby ensuring sufficient hydration reaction and longer operating time.
Reinforcing materials:
Cellulose ethers used to enhance the strength of cement products need to have good dispersibility and moderate viscosity to enhance the uniformity and strength of the matrix.
3. Optimize the addition method
Controlling the addition method of cellulose ether in cement products is crucial to maximize its effectiveness. The following are several common optimization methods:
Premixing method:
Mix cellulose ether with other dry powder materials in advance. This method can avoid the formation of agglomeration of cellulose ether after direct contact with water, thereby ensuring its uniform dispersion in the slurry.
Wet mixing method:
Add cellulose ether to cement slurry gradually. This method is suitable for the situation where cellulose ether dissolves quickly and helps to form a stable suspension.
Segmented addition method:
In the process of preparing cement slurry, adding cellulose ether in segments can ensure its uniform distribution throughout the preparation process and reduce agglomeration.
4. Control external factors
External factors such as temperature, pH value, and stirring rate have a significant impact on the performance of cellulose ether.
Temperature control:
The solubility and viscosity of cellulose ether are very sensitive to temperature. Higher temperatures help cellulose ether to dissolve quickly, but may also cause the viscosity of the solution to decrease. The temperature should be adjusted according to the specific application scenario to ensure optimal operability and performance.
pH adjustment: The pH value of cement paste is usually in the high alkaline range, while the solubility and viscosity of cellulose ether fluctuate with the change of pH value. Controlling the pH value within the appropriate range can stabilize the performance of cellulose ether.
Stirring rate: The stirring rate affects the dispersion effect of cellulose ether in cement paste. Too high stirring rate may lead to air introduction and aggregation of cellulose ether, while moderate stirring rate helps to evenly distribute and dissolve cellulose ether.
5. Case analysis and practical suggestions
Through actual case analysis, we can further understand the application and optimization strategy of cellulose ether in different cement products:
High-performance tile adhesive: When a company was producing high-performance tile adhesive, it was found that the water retention of the original product was insufficient, resulting in a decrease in bonding strength after construction. By introducing high-water-retaining HEMC and adjusting its addition amount and addition method (using the premixing method), the water retention and bonding strength of the tile adhesive were successfully improved.
Self-leveling floor material: The self-leveling floor material used in a certain project had poor fluidity and poor surface flatness after construction. By selecting low-viscosity HPMC and optimizing the stirring rate and temperature control, the fluidity and construction performance of the slurry are improved, making the final floor surface smoother.
Controlling the performance of cellulose ether in cement products is the key to improving material performance and construction quality. By selecting the right type of cellulose ether, optimizing the addition method, and controlling external influencing factors, the key properties of cement products such as water retention, adhesion, and fluidity can be significantly improved. In practical applications, it is necessary to continuously optimize and adjust the use of cellulose ether according to specific needs and application scenarios to achieve the best results.
Post time: Jun-26-2024