Sodium carboxymethyl cellulose, referred to as carboxymethyl cellulose (CMC) is a kind of high-polymer fiber ether prepared by chemical modification of natural cellulose. Its structure is mainly D-glucose unit through β (1→4) The keys are linked together.
CMC is white or milky white fibrous powder or granules, with a density of 0.5-0.7 g/cm3, almost odorless, tasteless, and hygroscopic. Easily dispersed in water to form a transparent colloidal solution, insoluble in organic solvents such as ethanol. The pH of 1% aqueous solution is 6.5-8.5, when the pH>10 or <5, the viscosity of the mucilage decreases significantly, and the performance is the best when the pH=7. Stable to heat, the viscosity rises rapidly below 20°C, and changes slowly at 45°C. Long-term heating above 80°C can denature the colloid and significantly reduce the viscosity and performance. It is easily soluble in water and the solution is transparent; it is very stable in alkaline solution, but it is easily hydrolyzed when it encounters acid, and it will precipitate when the pH value is 2-3, and it will also react with multivalent metal salts.
Structural formula: C6H7(OH)2OCH2COONa Molecular formula: C8H11O5Na
The main reaction is: the natural cellulose first undergoes alkalinization reaction with NaOH, and with the addition of chloroacetic acid, the hydrogen on the hydroxyl group on the glucose unit undergoes a substitution reaction with the carboxymethyl group in the chloroacetic acid. It can be seen from the structural formula that there are three hydroxyl groups on each glucose unit, that is, C2, C3, and C6 hydroxyl groups. The hydrogen on each hydroxyl group is substituted by carboxymethyl, which is defined as a degree of substitution of 3. The degree of substitution of CMC directly affects the solubility, emulsification, thickening, stability, acid resistance and salt resistance of CMC .
It is generally believed that when the degree of substitution is around 0.6-0.7, the emulsifying performance is better, and with the increase of the degree of substitution, other properties are improved accordingly. When the degree of substitution is greater than 0.8, its acid resistance and salt resistance are significantly enhanced. .
In addition, it is also mentioned above that there are three hydroxyl groups on each unit, that is, the secondary hydroxyl groups of C2 and C3 and the primary hydroxyl group of C6. In theory, the activity of the primary hydroxyl group is greater than that of the secondary hydroxyl group, but according to the isotopic effect of C, the -OH group on C2 It is more acidic, especially in the environment of strong alkali, its activity is stronger than C3 and C6, so it is more prone to substitution reactions, followed by C6, and C3 is the weakest.
In fact, the performance of CMC is not only related to the degree of substitution, but also to the uniformity of the distribution of carboxymethyl groups in the entire cellulose molecule and the substitution of hydroxymethyl groups in each unit with C2, C3, and C6 in each molecule. related to uniformity. Since CMC is a highly polymerized linear compound, and its carboxymethyl group has inhomogeneous substitution in the molecule, the molecules have different orientations when the solution is left standing, and the length of the linear molecule is different when there is a shear force in the solution. The axis has a tendency to turn to the flow direction, and this tendency becomes stronger with the increase of the shear rate until the final orientation is completely arranged. This characteristic of CMC is called pseudoplasticity. The pseudoplasticity of CMC is conducive to homogenization and pipeline transportation, and it will not taste too greasy in liquid milk, which is conducive to the release of milk aroma. .
To use CMC products, we need to have a good understanding of the main parameters such as stability, viscosity, acid resistance, and viscosity. Know how we choose the right product.
Low-viscosity CMC products have a refreshing taste, low viscosity, and almost no thick feeling. They are mainly used in special sauces and beverages. Health oral liquids are also a good choice.
Medium-viscosity CMC products are mainly used in solid drinks, ordinary protein drinks and fruit juices. How to choose depends on the personal habits of engineers. In the stability of dairy beverages, CMC has contributed a lot.
High-viscosity CMC products have a relatively large application space. Compared with starch, guar gum, xanthan gum and other products, the stability of CMC is still relatively obvious, especially in meat products, the water retention advantage of CMC is more obvious! Among stabilizers such as ice cream, CMC is also a good choice.
The main indicators to measure the quality of CMC are degree of substitution (DS) and purity. Generally, the properties of CMC are different if the DS is different; the higher the degree of substitution, the stronger the solubility, and the better the transparency and stability of the solution. According to reports, the transparency of CMC is better when the degree of substitution is 0.7-1.2, and the viscosity of its aqueous solution is the largest when the pH value is 6-9.
In order to ensure its quality, in addition to the choice of etherification agent, some factors that affect the degree of substitution and purity must also be considered, such as the relationship between the amount of alkali and etherification agent, etherification time, water content in the system, temperature, DH value, solution Concentration and salt etc.
The quality of CMC finished products mainly depends on the solution of the product. If the solution of the product is clear, there are few gel particles, free fibers, and black spots of impurities, it is basically confirmed that the quality of CMC is good. If the solution is left for a few days, the solution does not appear. White or turbid, but still very clear, that is a better product!
Post time: Dec-14-2022