Influence of degree of substitution (DS) on CMC Quality
Sodium carboxymethylcellulose (CMC for short) is a kind of high-polymer cellulose ether made from natural cellulose by chemical modification. CMC thickener is a widely used and the most cost-effective thickening agent.
As can be seen from the structure formula, there are three hydroxyl groups in each glucose unit, namely C2, C3, and C6 hydroxyl groups. The number of hydrogen in hydroxyl group of glucose unit replaced by carboxymethyl can be expressed by degree of substitution (DS). If all the three hydroxyl groups in each glucose unit are replaced by carboxymethyl, the degree of substitution can be defined as 3. The degree of substitute has a direct impact on the solubility, emulsibility, thickening property, stability, acid resistance and salt tolerance.
It is generally thought that Sodium carboxymethylcellulose has better emulsifying property when the degree of substitution is 0.6-0.7. Furthermore, with the increase of DS, other properties can be improved accordingly. When the degree of substitution is over 0.8, the resistance to acids and salts can be remarkably enhanced.
Since Sodium carboxymethylcellulose is a high-polymer linear compound and there exists substitutional inhomogeneity of carboxymethyl in the molecule, the molecules have different orientations when the solution is let sit. When there is shearing force in the solution, the long axis of linear molecule will have a tendency of turning to the flow direction.
Moreover, the tendency will become stronger with the increase of shearing rate till it finally completes the directional alignment. This property of Sodium carboxymethylcellulose is called pseudo plasticity. The pseudo plasticity of Sodium carboxymethylcellulose helps to reduce the energy consumption of liquid milk production and is beneficial for homogeneous and channelization delivery. In addition, the taste of liquid milk won’t be too greasy and it is also good for the release of milk fragrance.
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