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Main properties and product introduction of sodium carboxymethyl cellulose

2021-06-04

Ⅰ. Properties and product introduction of sodium carboxymethyl cellulose

Sodium carboxymethyl cellulose (CMC) is a highly polymerized cellulose ether made from natural cellulose through chemical modification. Its structure is mainly composed of D-glucose units connected by β(1→4) glycosidic bonds.

CMC is white or creamy white fibrous powder or granule, density 0.5-0.7g/cm3, almost odorless and tasteless, with hygroscopicity. It is easily dispersed in water into transparent gel solution, insoluble in organic solvents such as ethanol. The pH of 1% aqueous solution is 6.5~8.5. When pH>10 or <5, the viscosity of the slurry decreases significantly, and the performance is best at pH=7. Stable to heat, viscosity rises rapidly below 20℃, changes slowly at 45℃, prolonged heating above 80℃ can make its colloid denatured and viscosity and performance decrease. It is easily soluble in water. The solution is transparent; it is stable in alkaline solution but easily hydrolyzed when it meets acid. It will precipitate when the pH value is 2-3 and will react with multivalent metal salts to sink.

Structural formula: C6H7(OH)2OCH2COONa      
Molecular formula: C8H11O5Na

The main reaction is that natural cellulose firstly reacts with NaOH by alkylation. With the addition of chloroacetic acid, the hydrogen on the hydroxyl group on its glucose unit reacts with the carboxymethyl group in chloroacetic acid by substitution. It can be seen from the structural formula that there are three hydroxyl groups on each glucose unit, namely C2, C3, and C6 hydroxyl groups. The number of hydrogens on the hydroxyl groups of glucose units substituted by carboxymethyl is expressed by the degree of substitution. If the hydrogens on all three hydroxyl groups on each unit are substituted by carboxymethyl, the degree of substitution is defined as 3. The size of the degree of substitution of CMC directly affects the solubility, emulsification, thickening, stability, acid resistance, and salt resistance of CMC. 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 the emulsification performance is better when the degree of substitution is around 0.6~0.7, and other properties will be improved accordingly with the increase of the degree of substitution. When the degree of substitution is more than 0.8, the acid and salt resistance will be enhanced significantly.

In addition, it is also mentioned above that there are three hydroxyl groups on each unit, namely C2, the secondary hydroxyl group of C3, and the C6 primary hydroxyl group. Theoretically, the primary hydroxyl group is more active than the secondary hydroxyl group. Still, according to the homotopy effect of C, the -OH group on C2 is more acidic, especially in the environment of strong bases its vitality is stronger than C3 and C6, so it is more likely to undergo substitution reactions, C6 is the second and C3 is the weakest.


CMC's performance is related to the size of substitution and the uniformity of the distribution of carboxymethyl groups in the whole cellulose molecule and the uniformity of hydroxymethyl substitution with C2 C3 and C6 in each unit of each molecule. Since CMC is a highly polymerized linear compound, and there is the unevenness of substitution of carboxymethyl groups in the molecule, the molecules have different orientations when the solution is stationary. When there is a shear force in the solution, the long axis of the linear molecules tends to turn to the flow direction. With the increase of shear rate, the stronger this tendency is, until the final completely oriented arrangement, this characteristic of CMC is called pseudoelasticity. This property of CMC is called pseudoelasticity. Neuroplasticity is good for homogenization and pipeline transport, not too greasy in liquid milk, and good for releasing milk aroma.


Using CMC products, the main thing is that we need to have enough understanding of the stability, viscosity, acid resistance, viscosity, and other major index parameters. Know how we can choose the right product.

Low viscosity CMC products, refreshing taste, low viscosity, almost no thick feeling, mainly used in special sauces and beverages, health care oral liquid is also a good choice.

Medium viscosity CMC products, mainly used in solid drinks, ordinary protein drinks, and fruit juices, how to choose, according to the engineer's habits.

High viscosity CMC products, application space, is relatively large, compared to starch, guar gum, xanthan gum, and other products, the stability of CMC is still more obvious, especially in meat products, CMC's water retention advantage is more obvious! Ice cream and other stabilizers, CMC is also a good choice.

The main indicators to measure the quality of CMC are the degree of substitution (DS) and purity. Generally, DS is different, the properties of CMC are also different; the degree of substitution increases, the solubility is enhanced, and the transparency and stability of the solution are better. CMC's transparency is better when the degree of substitution is 0.7~1.2, and the viscosity of its aqueous solution is maximum when the pH is 6~9.

To ensure its quality, in addition to the choice of etherizing agent, some factors affecting the degree of substitution and purity must be considered, such as the relationship between the amount of alkali and etherizing agent, etherification time, system water content, temperature, DH value, solution concentration, and salts, etc.

CMC finished product quality mainly depends on the product solution. If the product solution clear, gel particles less, less free fiber, fewer impurities black spot, basically determine the quality of CMC good, if the solution is placed for a few days, the solution does not appear whitish or turbid, or very clear, that is a better product minion!



Ⅱ. Dissolution and dispersion of CMC products

Mix CMC directly with water and prepare it into paste gum, and then set aside. When configuring the CMC paste, first add a certain amount of clean water into the batching cylinder with a stirring device, and then spread the CMC slowly and evenly into the batching cylinder with the stirring device on, constantly stirring so that the CMC and water are completely integrated, and the CMC can be fully dissolved.



Ⅲ.  Answers to the questions in the use of CMC

Q: How do low viscosity, medium viscosity, and high viscosity differentiate from each other in terms of structure, and will the consistency be different?
A:It is understood that the molecular chain length is different, or the molecular weight is different, divided into low, medium, and high viscosity, the macro performance, of course, corresponds to the viscosity is different, the same concentration, viscosity has high and low, the stability of the product and acid ratio and so on is not directly related, mainly depends on the product solution.




Q: What is the specific performance of the products with the substitution degree of 1.15 or above, or the higher the substitution degree, the specific performance of the products is enhanced.

A: Product substitution degree is high, liquidity increases, pseudo-plasticity is reduced, the same viscosity of the product, high substitution degree, slipperiness is more obvious, high substitution degree product solution has a glossy, general substitution degree product, solution whitish.

Q: Is it enough to choose medium viscosity to make fermented protein drinks?

A:Medium to low viscosity products, substitution degree of about 0.90, and better acid resistance products.


Q: How can CMC dissolve quickly? I sometimes use it and boil it, but it still dissolves more slowly?

A: Use other colloids miscible, or use 1000-1200 speed stirrer to disperse, CMC dispersion is not good, good hydrophilicity, easy to clump, high degree of substitution products more obvious! Warm water dissolves faster than cold water dissolve speed, generally do not recommend boiling, CMC products for a long time boiling will destroy the molecular structure, the product will lose viscosity!