Relationship between water retention of cellulose and use temperature

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The greater the amount of cellulose ether added in the mortar, the better the water retention performance, the higher the viscosity, the better the water retention performance.

For particle size, the finer the particles, the better the water retention. Large particles of cellulose ether and water contact, the surface immediately dissolved to form a gel material wrapped up to prevent water molecules continue to penetrate, sometimes long time stirring can not be evenly dispersed dissolved, the formation of a turbid flocculent solution or agglomeration. Greatly affect the water retention effect of cellulose ether, solubility is one of the elements of the choice of cellulose ether. Fineness is also an important performance index of methyl cellulose ether. The cellulose used for dry powder mortar is required to be powder with low water content, and the fineness also requires that the particle size of 20% to 60% is less than 63um. The fineness affects the solubility of the methyl cellulose ether. Coarse cellulose is usually granular, it is easy to dissolve in water without caking, but the dissolution rate is very slow, it is not suitable for use in dry mortar. In dry mortar, cellulose is dispersed between cementitious materials such as aggregate, fine filler and cement. Only fine enough powder can avoid methyl cellulose ether agglomeration when mixing with water. When cellulose is added with water to dissolve the agglomerates, it is difficult to dissolve in dispersion. The fineness of the coarse cellulose not only waste, but also reduce the local strength of the mortar, such dry mortar large area construction, the performance of the local dry mortar curing speed is significantly reduced, due to different curing time caused by cracking. For the use of mechanical construction of spray mortar, due to the mixing time is shorter, the fineness of the requirements are higher.

The fineness of cellulose also has a certain effect on its water retention. Generally speaking, for methyl cellulose ethers with the same viscosity and different fineness, the finer the water retention effect is better under the same addition amount.

The water retention of cellulose is also related to the temperature of use, and the water retention of methyl cellulose ether decreases with the increase of temperature. However, in the actual application of materials, dry mortar in many environments is often constructed on hot substrates at high temperatures (higher than 40 degrees), such as exterior putty plastering in the case of sun in summer, which often accelerates the curing of cement and the hardening of dry mortar. The decrease of water retention rate leads to the obvious feeling that both workability and cracking resistance are affected. Under this condition, it is particularly critical to reduce the influence of temperature factors. Although methyl hydroxyethyl cellulose ether additives are currently considered to be at the forefront of technological development, their dependence on temperature still leads to a weakening of the performance of dry mortar. Despite increasing the amount of methyl hydroxyethyl cellulose (summer formula), the workability and anti-cracking properties still cannot meet the needs of use. Cellulose through some special treatment, such as improving the degree of etherification, can make its water retention effect in the case of higher temperature to maintain a better effect, so that it provides better performance in harsh conditions.

Key words:

Mortar additive