Sodium carboxymethylcellulose, or simply carboxymethyl cellulose (CMC), is a highly polymeric cellulose ether made by natural cellulose through chemical modification. Whose structure is mainly composed of D-glucose units connected by (14) glycosidic bonds.CMC is a white or milky white fibrous powder or particles with a density of 0.5-0.7 g / cm cm. It is easily dispersed in water into a transparent colloidal solution, insoluble in organic solvents such as ethanol. The 1% aqueous solution pH was 6.5 to 8.5, and the plasp viscosity was significantly reduced when pH> 10 or.
The main reaction is:
natural cellulose first alkalization reaction with NaOH, with the addition of chloroacetic acid, the hydrogen on the hydroxyl group on the glucose unit and the carboxymethyl group in chloroacetic acid substitution reaction.It can be seen from the structure of three units on each unit hydroxyl, namely C2, C3, C6 hydroxyl, glucose unit on the hydroxyl hydrogen by carboxymethyl substitution represented by the hydrogen on each unit by carboxymethyl, defined as the substitution is 3, the size of CMC substitution directly affect the CMC solubility, emulsification, thickening, stability, acid resistance and salt resistance performance.
It is generally believed that the emulsification performance is better when the substitution degree is around 0.6~0.7. But with the improvement of the substitution degree, other properties are improved accordingly. When the substitution degree is greater than 0.8, its acid resistance and salt resistance are significantly enhanced.In addition, the above also mentioned a total of three hydroxyl on each unit, C2, C3 and C6, theoretically more activity than secondary hydroxyl, but according to the isotopic effect of C, -OH group on C2 is more acidic, especially in the environment of strong base its vitality is stronger than C3, C6, so more prone to substitution reaction, C6 times, C3 is the weakest.
In fact, the performance of CMC is not only related to the size of the substitution degree. But also related to the uniformity of the distribution of the carboxyl methyl groups in the whole cellulose molecule and the uniformity of the hydroxyl methyl group in each molecule with C2, C3 and C6 substitution in each unit. Because CMC is highly polymerization linear compound, and its carboxymethyl group in the molecule substitution inhomogeneity. So when the solution has different orientation, when the solution shear force. The long axis of the linear molecule to the flow direction, and the trend as the shear rate is stronger, until the final completely directional arrangement. This property of CMC is called pseudoplastic.