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.
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.