PAC & CMC knowledge Product Features

1、Product Overview

Product Name: CMC-Na (Sodium Carboxymethyl Cellulose), customarily shorten form CMC, the abbreviation is CMC. CMC is a representative cellulose ethers, its sodium salt used widely in industry, CMC belongs to anionic polymer electrolyte, besides CMC-Na, it has other salt, such as ammonium and aluminum salt. CMC sometimes can change to CMC acid. D.S, that is the average of the hydroxyl which reacts with substitute on each anhydrous glucose unit, when D.S is 1:00, its molecular formula is [C6H7O2(OH)2OCH2COONa]n,
Structure general wrote as follows:

2、Main Properties of Products
2.1 Appearance
CMC is odorless, tasteless, non-toxic white powder or micro-yellow fibrous in pure state.
2.2 Solubility
CMC is easy to absorb moisture, it dissolves easily in cold or hot water as colloidal solution, it can not dissolve in many organic solvents such as methanol, ethanol, acetone, chloroform, benzene and so on. The degree of substitution (D.S) is an important factor affects its water-soluble, the viscosity also affects its water-soluble greatly. CMC is usually alkali when viscosity between 25mPa.s-50000mPa.s, D.S is about 0.3. CMC is water-soluble when its D.S is more than 0.4. With the increase of D.S, the transparency of the CMC water substitution becomes much better. Like other macromolecule dielectric, when CMC dissolving, the first phenomenon is expansion, and then dissolved gradually. So in preparation solution, the particles should be uniform wetting, then the CMC can be dissolved quickly. Otherwise, the CMC are expansion in water solution, the particles form a strong involucres or plastic coating, so that the particles scattered difficulty resulting dissolution difficulty.
2.3 Hygroscopic Nature
The balance moisture of CMC with the increase of air humidity increased, with the rise in temperature decreases. At room temperature and the average humidity 80-85%, the balance of moisture more than 26 percent, however the moisture of products less than 10%, lower than the balance moisture. Even if the moisture content at about 15 percent, there have no difference in appearance. But when moisture content at more than 20 percent, some particles adhere to one another will be able to see, the higher the viscosity, the more obvious of the phenomenon.
The CMC is a polarity macromolecule compound, its degree of absorbing moisture dominated by the relative humidity, but also the number of polarity group. The higher the D.S, that is, if the number of polarity group is larger, the degree of absorbing moisture is bigger.
2.4 Solution Viscosity
2.4.1 The viscosity of CMC water solution is the specific performance of Polymerization Degree of the cellulose, it depends on the average degree of materials cellulose, and the degradation of polymerization degree in the course of basification and etherification reaction, including the reaction uniformity. The viscosity of the CMC solution with the increase of its concentration, and the increase trend was similar to a straight line. Solution viscosity have relative with the polymerization degree of the cellulose and its distribution, but also have relative with the solution concentration, pH value, temperature, velocity gradient, D.S and so on.
2.4.2 The Effect Factors of Viscosity
A, Concentration: Regardless of high, medium and low viscosity of the CMC, the viscosity increased with its concentration increase, the logarithm value about concentration and viscosity is approximating beeline.
B, pH Value: The viscosity of the 1% CMC solution is in the largest and most stable state when pH value at 6.5-9.0. Generally, the changes of the viscosity is not very large when the pH at 9.0-11.0. However, PH <6, the viscosity will decline rapidly, and began to form CMC acid, and decline entirely when PH ≌ 2.5; if PH> 9, the viscosity will decline also, at first decline slowly, but when the PH> 11.5, it began a sharp decline. This is because the un-substitution hydroxyls combined with the base molecules, and promote cellulose scattered.
C, Temperature: The viscosity of the CMC solution with increase of temperature. When cooling, the viscosity will rebound, but when the temperature rose to a certain extent, it will be in permanent lower viscosity state. The decline of the viscosity has a closely related to its degree of substitution, the higher the D.S, the viscosity less affected by temperature.
D, Impact of Salt: The existence of all kinds of inorganic salt ions would reduce the viscosity of CMC solution, the effect almost depends on the value of the cation. Generally, it is water-soluble salt when met one value cation, it is water-insoluble salt when met trivalent cation, the water-soluble is between one and trivalent when met bivalent cation.
E, Impact Velocity Gradient: Because the CMC solution is non-Newtonian fluid, but belongs to the pseudoplastic fluid. Their mobile properties can not be depicted by a simple Newton's formula, but the apparent viscosity of the solution is still the function of velocity gradient at determining.
For Newtonian fluid, the relationship of its velocity gradient and tangential force is direct proportional. For pseudoplastic fluid, the increase of the velocity gradient with the increase of tangential force is faster than a straight line, that is to see, the viscosity will reduce with the increase of the tangential force.
For the CMC solution, its viscosity changes with the velocity gradient can be explained: Because the dispersed phase of CMC is hydrophilic, after sopping water, at first it will expansion, and then dissolved as macromolecules. Because the volume of the molecules is large, the viscosity is great. If the tangential force is increasing, the macromolecules begin directional function, the long axis will be gradually transformed into the flow direction, and the tangential force bigger, the more complete the turning, so the viscosity resistance becoming smaller when the CMC solution flowing. At the same time, the solvent layer around the CMC can also be deformed due to tangential force changing, which is the reason for the resistance reducing. In low concentrations CMC solution, velocity gradient affect on the viscosity is very small, when the solution concentration increases, the velocity gradient affect on viscosity also increases.
F, The viscosity of the CMC solution will increase with the D.P increasing, but the increase rate of the viscosity is different because of the degree of substitution.
2.5 CMC will deposit when met with heavy metal salts, such as PbSO4, FeCl3, FeSO4, CuSO4, K2Cr2O7, AgNO3, SnCl2, and so on.

1、The structure of PAC

The difference of structure between PAC and CMC was analyzed by the technology of H-NMR, the result shown in Figure 1.


Figure 1 The H-NMR NMR spectrum of CMC and the PAC

Chemical shift 3.0-4.0 is the peak of the proton on glucose units, 4.0-4.5 is the characteristic peak of -CH2COO, 4.5-5.5 is resonance peak caused by the proton on the reduction of terminal C(1) of glucose unit. Use Dolby DS value and the changes of proton displacement signal strength on C(1) to find that carboxymethylation of the hydroxyl on C(2) led to C(1) proton displacement decline. The distribution of - CH2COO on three positions of PAC linked glucose molecules unit is more uniformity than CMC. There are two reasons, on the one hand the solid-liquid mass transfer fully and complete alkalization during the production process of the PAC, under the strong attack of cellulose conformation change, the hydrogen bonds of macromolecules were weaken uniformity, or even open, see Figure 2, reduced the alkalization and etherification reaction barriers of on C(2), C(3), C(6), averaged the response capability, and has effectively improved the reaction speed and capacity. On the other hand, due to the adjustment of techniques to ensure that the heat of the reaction proliferated by time of alkalization reaction and in the initial of etherification reaction, to avoid local alkalization reaction blind spots and reduce the side reactions, greatly enhance the uniformity of the distribution of - CH2COONa in product at the macro (the different regions of reactor) and micro (on the different Central of the macromolecules linked cellulose) .


Figure 2 Macromolecular Conformation


Compared with the CMC, the distribution of CH2COO- group within macromolecules chain of PAC are more uniformly, in the acidic environment ,the ability and extent tend to curl of the CH2COO-group within difference glucose units of the whole macromolecules chain are same, in different macromolecules chain also similar. The degree of the reducing of overall viscosity is lessening, and good performance for the antacid. From the test results of milk application, PAC has the better application performance than CMC.

2、Molecular weight

The produce of PAC using special technology and process, at the same degree of substitution and viscosity, PAC molecular weight is lager than the CMC, about one magnitude. 

3、Distribution uniformity of the substitute groups

Macromolecules chain can be regard as embed copolymer composed of glucose-ring with substitute groups (expressed by A) and non-substitute groups (expressed by B). -CH2COONa on glucose-ring with substitute groups represents anions. The uniform distribution of characteristics groups in structure of PAC shown in Figure 3.

Figure 3 The sketch map of uniform distribution of charcteristics groups

4、Rheological property


Rheological property tested by RHEOTEST-2-spin-viscosity, at 25 ℃.
Same as the conventional polymer-electrolyte solution, the molecular chain of PAC will degradation and chain-cutting with the shear stress occurs, or strong stirring in solution will make the inter-space network formed from macromolecules damage. The results shows, compared with the CMC, the extent of PAC solution properties change is smaller, the compared results shown in Figure 4.



Figure 4 PAC and CMC rheological properties

In solid-state, the cellulose molecule chain-gathering forming different levels of the original fiber structure, normally, we used the theory of “tassel-cellulose” structure to describe the cellulose-gathering structure of the original cellulose, molecule chain can get through crystal areas and amorphous crystal areas continuously, crystal areas and amorphous crystal areas have no clear boundaries, but by the order of high-order state to low-order state gradually. This determines the chemical reactions from low-order area and began a gradual transition to high sequence, it cause that the different water loss glucose units on the same molecular chain have different D.S, and some of them can not be Substituted. For the partly substitution cellulose, there must exist un-substituted glucose units, and caused the products have a certain degree crystallization, it has been confirmed by using X-ray diffraction to determine the carboxyl. On the cellulose molecule chain, the primary hydroxyl group, the second hydroxyl group and the aglycon bond within water loss glucose unit have relate with the chemical nature, the aglycon bond is very stable and not easily broken, also do not form hydrogen bonds with other hydrogen-bond, therefore, the chemical reaction and reaction uniformity of cellulose usually come down to three hydroxyl. Generally, three hydroxyl of water loss glucose (AGU) can not be fully transformed, it only can be received partly substituted product, it is because:
(1) When one or two hydroxyl on AGU be substituted, three-dimensional obstacle effect will make the remaining hydroxyl not fully react;
(2) to the special reagents and reaction conditions, not all the hydroxyl can be attacked ;
(3) and in all the attacked hydroxyl, to different hydroxyl, the reactive properties and reactive rate are difference. Therefore, it causes the substitution proportion of the three hydroxyls on each of the AGU not equality. D.S, and the uniformity of the substitution group distribution are the key factor impact on product performance, they are also the decisive factor to distinguish PAC and CMC, The D.S and purity of CMC are lower, but impurities is higher, substituted group on the AGU are distribution non-serious; however, The D.S and purity of PAC are higher, but impurities is lower, substituted group on the AGU are distribution more uniform.