 | Cellulose is a biopolymer made up of glucose units linked in a linear chain formation. For each anhydroglucose unit there are three hydroxyl groups (OH groups) which provide reactive centres where a variety of chemical reactions can take place.
Unmodified cellulose is not soluble in water or in conventional solvents. By etherifying the hydroxyl groups it is possible to use so-called substituents to convert the cellulose into water-soluble or in some specific cases into organo-soluble derivatives
| WalocelŪ M - type of substitution | Abbreviation | Manufacture | Graphic formula of a possible glucose unit |
| Methylhydroxypropyl cellulose | MHPC | Conversion of alkali cellulose using methyl chloride and propylene oxide |  |
| Methylhydroxyethyl cellulose | MHEC | Conversion of alkali cellulose using methyl chloride and ethylene oxide |  |
By controlling the reaction conditions it is possible to regulate the degree of etherification very precisely.
As a measure of the degree of conversion, two characteristics of methylhydroxyalkyl cellulose are specified:
- the degree of substitution (DS)
- the molar degree of substitution (MS)
The degree of substitution indicates the average number of etherified hydroxyl groups in a glucose unit, whereas the molar degree of substitution indicates the average number of bonded hydroxyalkyl groups per anhydroglucose unit. As an anhydroglucose unit has three hydroxyl groups available for conversion, the maximum obtainable degree of substitution DS = 3. Since ethylene oxide and propylene oxide can form side chains during the reaction, there is theoretically no limit to the value of the molar degree of substitution.
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