Cellulose ether refers to cellulose derivatives on which hydroxyl groups are partially or completely substituted by ether groups. In dry mixed mortar products, the addition of cellulose can significantly improve the performance of mortar. Therefore it is an important additive in dry mixed mortar products.
Cellulose ether can be divided into anionic type, cationic type and non-ionic type according to the different chemical structure of ether substituents. Nonionic ether, which is mostly used in mortar products, can also be divided into water-soluble ether and oil-soluble ether. Monosubstituted ether refers to the kind where there is only one type of substituent on the cellulose ether molecular chain, while mixed ether refers to where there are two or more different substituents on the subchains
Cellulose ethers used in the building materials are mainly methyl cellulose ether (MC), hydroxypropyl methyl cellulose ether (HPMC), hydroxyethyl methyl cellulose ether (HEMC), hydroxyethyl cellulose ether (HEC), hydroxyethyl ethy cellulose ether (EHEC), etc. Among them, HPMC and HEMC have been widely used in dry mixed mortar products due to their excellent characteristics.
Cellulose ether etherification is carried out under alkaline conditions. Cellulose reacts with alkali solution to produce swelling alkali cellulose, and then reacts with etherification reagent. The mixed cellulose ether can be prepared by adding different etherification reagents simultaneously or in sections during the reaction.
The mechanism of cellulose ether in mortar mainly depends on its water retention ability which comes from the solubility and dehydration of cellulose ether itself. Cellulose molecular does not dissolve in water although it contains a large number of hydroxyl groups. This is because the hydroxyl groups are not strong enough to break the strong hydrogen bonds and van der Waals forces between molecules. Cellulose only swells in water but not dissolve.
After introduction of substituent in molecular chain, the hydrogen bonds inside and between the molecular structures are destroyed. The bigger effect of destruction of hydrogen bond, the greater viscosity of cellulose ether solution you will get. When temperature increases, the hydration of the polymer decreases and the molecule begins to aggregate, forming a three-dimensional network structure gel to precipitate from solution.
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