Research on quality of cellulose ethers used in dry mortar
In recent years, with the gradual implementation of the relevant policies of adhering to the scientific development concept and building a resource-conserving society, China’s construction mortar is facing a revolution from traditional mortar to dry-mix mortar. The construction of dry-mix mortar industry has entered rapid development. trail of. As the most important admixture in building dry-mix mortar products, cellulose ether plays a key role in the performance and cost of dry-mixed mortar. There are two types of cellulose ethers: one is ionic, such as sodium carboxymethyl cellulose (CMC), and the other is nonionic, such as methyl cellulose (MC), hydroxyethyl cellulose (HEC), Hydroxypropyl methylcellulose (HPMC) and the like. Currently, most of the global cellulose ether products are used in building materials.
With the rapid development of the dry-mix mortar industry, China’s cellulose ether has basically achieved localization, and the situation of foreign product control market has been broken. With the increasing popularity of dry-mixed mortar products, China will become the world’s largest producer of dry-mixed mortar. The application of cellulose ether will further increase, and its manufacturers and products will be more and more. How the performance of cellulose ether in dry mortar is the focus of the producer and the user.
The most important property of cellulose ethers is their water retention in building materials. If no cellulose ether is added, the thin layer of fresh mortar will dry out quickly, making the cement unable to hydrate in the normal way, resulting in the mortar not hardening and good adhesion. At the same time, the addition of cellulose ether makes the mortar have good plasticity and flexibility, and improves the bonding strength of the mortar. Let’s talk about the impact on the application of dry mortar from the product properties of cellulose ether.
۱, the fineness of cellulose ether
The fineness of cellulose ether affects its solubility. For example, the lower the fineness of cellulose ether, the faster its dissolution rate in water and the better water retention performance. Therefore, cellulose ether fineness should be included in one of its investigation properties. In general, the sieve opening of cellulose ether fineness exceeding 0.212 mm should be no more than 8.0%.
۲, weight loss rate
The weight loss rate of drying refers to the drying of cellulose ether at a certain temperature, and the mass of the lost material accounts for the percentage of the mass of the original sample. For a certain quality of cellulose ether, the weight loss rate is too high, which will reduce the content of active ingredients in cellulose ether, affect the application of downstream enterprises, and increase the purchase cost. Generally, the weight loss rate of cellulose ether drying is not more than 6.0%.
- Sulfate ash of cellulose ether
For a certain amount of cellulose ether, the ash content is too high, which will reduce the content of active ingredients in cellulose ether, affecting the application effect of downstream enterprises. The sulfated ash of cellulose ether is an important measure of its own performance. In combination with the current production status of cellulose ether production enterprises in China, the ash content of MC, HPMC and HEMC should not exceed 2.5%, and the ash content of HEC cellulose ether should be no more than 10.0%.
۴, the viscosity of cellulose ether
The water retention and thickening of the cellulose ether is mainly determined by the viscosity and the amount of the cellulose ether itself added to the cement slurry.
- PH value of cellulose ether
After the cellulose ether product is stored at a higher temperature or for a longer period of time, the viscosity gradually decreases, and the performance of the high viscosity product is particularly remarkable, so the pH is required to be limited. It is generally preferred that the pH range of the cellulose ether be controlled to be 5-9.
۶, the transmittance of cellulose ether
The light transmittance of cellulose ether directly affects its application effect in building materials. The main factors affecting the transmittance of cellulose ether are: (1) the quality of raw materials; (2) the effect of alkalization; (3) the process Proportion; (4) solvent ratio; (5) neutralization effect.
According to the effect of use, the transmittance of the cellulose ether should be not less than 80%.
- Gel temperature of cellulose ether
Cellulose ethers are primarily used as tackifiers, plasticizers, and water retention agents in cement products, so viscosity and gel temperature are important metrics for characterizing the quality of cellulose ethers. The gel temperature is used to determine the cellulose ether type, which is related to the degree of substitution of the cellulose ether. In addition, salts and impurities can also affect the gel temperature. When the temperature of the solution rises, the cellulose polymer gradually loses water, and the viscosity of the solution decreases. When the gel point is reached, the polymer is completely dehydrated to form a gel. Therefore, the temperature of the cement product is usually controlled below the initial gel temperature. Under this condition, the lower the temperature, the higher the viscosity, and the more obvious the viscosity-increasing water retention effect