Cellulose ether plays an irreplaceable role in the production of building materials, especially dry mixed mortar. Especially in the production of special mortar (modified mortar). It is an indispensable and important part.
The important role of water-soluble cellulose ether in mortar mainly has three aspects. One is excellent water retention ability. The second is the influence of mortar consistency and thixotropy. And the third is the interaction with cement.
Cellulose ether water retention depends on the base of hygroscopicity, composition of mortar, mortar layer thickness, mortar water demand, condensation material condensation time. The water retention of cellulose ether comes from the solubility and dehydration of cellulose ether itself.
It is well known that cellulose molecular chains, although they contain a large number of highly hydrated OH groups. They are insoluble in water because of their highly crystalline structure. The hydration ability of hydroxyl groups alone is not enough to pay for the strong intermolecular hydrogen bonds and van der Waals forces.
So, in water it only expands and does not dissolve. When substituents are introduced into a molecular chain. Not only the substituents destroy the hydrogen chain, but also the interchain hydrogen bonds are broken due to the wedging of substituents between adjacent chains. The greater the destruction of hydrogen bond effect, cellulose lattice expansion. The solution into the cellulose ether becomes water-soluble, the formation of high viscosity solution.
As the temperature rises, the hydration of the polymer decreases and the water between the chains is driven out. When the dehydrating effect is sufficient, the molecules begin to aggregate and the gel folds out in a three-dimensional network. The factors affecting the water retention of mortar include cellulose ether viscosity, dosage, particle fineness and service temperature.
The greater the viscosity of cellulose ether, the better the water retention performance, the viscosity of polymer solution. The molecular weight (degree of polymerization) of polymer is also determined by the length and morphology of the molecular structure of the chain. And the distribution of the number of substituents directly affects the viscosity range. [η] = Km alpha
[η] Intrinsic viscosity of polymer solutions
M polymer molecular weight
α polymer characteristic constant
K viscosity solution coefficient
The viscosity of polymer solution depends on the molecular weight of the polymer. The viscosity and concentration of cellulose ether solutions are related to various applications. Therefore, each cellulose ether has many different viscosity specifications. Viscosity regulation is also mainly through the degradation of alkali cellulose, namely the fracture of cellulose molecular chain to achieve.
As can be seen from Figure 1.2, the greater the amount of cellulose ether added to the mortar, the better the water retention performance. The higher the viscosity, the better the water retention performance.
For particle size, the finer the particle, the better the water retention is, as shown in Figure 3. When large particles of cellulose ether come into contact with water. The surface dissolves and forms a gel that wraps the material and prevents further infiltration of water molecules. Sometimes a long time stirring can not be evenly dispersed dissolution, the formation of a muddy flocculent solution or agglomerate. The solubility of cellulose ether is one of the factors to choose cellulose ether.