Classification and Functions of Cellulose Ethers
The cellulose ether is a general term for a series of products produced by reactions of alkali celluloses and etherifying agents under certain conditions. Different cellulose ethers will be obtained when alkali celluloses are substituted by different etherifying agents.
According to the ionizing performance of substituents, cellulose ethers can be divided into two categories: ionic(e.g. carboxymethylcellulose) and non-ionic (e.g. methyl cellulose).
According to the kinds of the substituents, cellulose ethers can be divided into monoethers (e.g. methyl cellulose), and mixed ethers (e.g. hydroxypropyl methylcellulose HPMC).
According to the difference of solubility, cellulose ethers can be divided into water-soluble type (e.g. Hydroxy ethyl cellulose) and the type of being soluble in organic solvents (e.g. ethyl cellulose). Dry-mixed mortar mainly use water-soluble celluloses, and water-soluble celluloses can be further divided into the instant type and the delayed dissolution type after the surface treatment.
The mechanism of action of cellulose ethers is as follows.
1). When the cellulose ethers in the mortar have dissolved in water, the surface activity effects ensure the gelling materials to be effectively and uniformly distributed in the system, and the cellulose ether, as a kind of protective colloid, can wrap solid particles and form a layer of lubricating film on the outer surface. Consequently, this helps to make the mortar system more stable and to improve the fluidity of mortar in the mixing process and the smoothness of construction.
2). Due to its own molecular structural features, the cellulose ether solution makes the moisture in the mortar not easy to lose and gradually release in a longer period of time, so gives mortar good water retention property. read…