Views: 0 Author: Site Editor Publish Time: 2023-06-13 Origin: Site
Abstract: Using carboxymethyl starch, carboxymethyl cellulose and hydroxypropyl methyl cellulose to compound, study the synergistic effect of carboxymethyl polysaccharides and hydroxypropyl methyl cellulose, and its thickening effect mechanism research. The results showed that both sodium carboxymethyl starch and sodium carboxymethyl cellulose had a certain synergistic effect on increasing the viscosity of non-ionic cellulose mixed ethers, and starch carboxymethyl had a stronger viscosity increasing effect than cellulose carboxymethyl. obvious.
Key words: carboxymethyl starch: carboxymethyl cellulose: hydroxypropyl methyl cellulose; thickening effect
Hydroxypropyl methylcellulose (HPMC) is a typical nonionic cellulose alkyl hydroxyalkyl mixed ether obtained by alkalization of cellulose and etherification of propylene oxide and methyl chloride. HPMC is used as a dispersant, water retaining agent, thickener and binder in building materials, and is mainly used in the molding of cement mortar and gypsum products. It is used in cement mortar to increase its cohesion, reduce flocculation, improve viscosity and shrinkage, and has the functions of water retention, reducing water loss on the concrete surface, improving strength, preventing cracks and weathering of water-soluble salts, etc. At the same time, I-IPMC has thixotropy, and can be formulated as a low-fluidity one-time thick coating for mortar and stucco coatings on vertical walls. The amount of HPMC in building materials is very small (0.1% to 1%), but it has a great effect. It is used as a plasticizer, tackifier, water retention agent, air-entraining agent and retarder for paint, plaster, mortar and cement products. , to increase its workability, water retention or adhesion to the base layer.
Sodium carboxymethyl starch (CMS) and sodium carboxymethyl cellulose (CMC) are common ionic polysaccharides, which have been widely used in medicine, food, textile, printing, papermaking, metallurgy, ll training in the fields of petroleum, foundry and daily chemical industry. CMS is similar to CMC in structure, so there are many similarities in properties: CMS has a high viscosity, is stable in neutral to alkaline solutions, and is easy to precipitate in strong acidic solutions; CMS has the inherent chelating properties of carboxyl groups, Ion exchange and flocculation of polyanions also have the functions of thickening, gelatinization, water absorption and adhesion of macromolecular solutions.
In order to obtain a building mortar with better dispersion, water retention, thickening and cohesion, which is a topic of concern in the industry at present, this study attempts to use the method of compounding HPMC, CMS, and CMC to study non-ionic mixed ethers and polyanions through comparative analysis. The viscosity, salt resistance, temperature resistance and other properties of polysaccharide ethers have a synergistic effect. Therefore, it can be applied in construction mortar, improve the dispersion, water retention, thickening and cohesive properties of mortar, and reduce the cost of mortar manufacturing.
1.1 Materials and Instruments
Sodium carboxymethyl starch, the viscosity of 5% aqueous solution is 3 Pa s; sodium carboxymethyl cellulose, the viscosity of 2% aqueous solution is 10 Pa s; three kinds of hydroxypropyl methylcellulose with different viscosities, Hebei Zhicheng Provided by Fine Chemical Company, the viscosities of 2% aqueous solutions are 43.5 Pa·s(1·), 88.5 Pa·S(2·), 120 Pa·s(3·).
NDJ-1 viscometer; JA21002 electronic balance, the actual division value is 0.1 g; AL104 electronic balance, the actual division value is 0.0001 g.
1.2 Preparation of mixture solution
Take a certain amount of hydroxypropylmethyl cellulose, carboxymethyl starch and carboxymethyl cellulose dried at 105°C for 2 h, mix CMS with I-IPMC, CMC and HPMC according to the mass ratio of 1:1, 1 : 3, 1: 4, 1: 5, 1: 8 and 1: 9 were weighed (accurate to 0.0001 g), and made into a mixed sample; the mixture was weighed, accurate to 1 mg, and prepared according to the dissolution method of HPMC 1% and 2% aqueous solution of the mixture were placed in an ice-water bath, stirred until a certain viscosity was produced, and allowed to stand for 3 h.
1.3 Temperature resistance test of mixture solution
Use the NDJ-1 viscometer to measure the viscosity of the solution at 20°C; place the mixture solution in a 40°C water bath at a constant temperature for 30 minutes, and measure the viscosity when the solution temperature is 40°C; measure the solution at 50, 60, and 70°C according to the above method. Viscosity at °C; plot the obtained data and observe the slope of the line, the smaller the slope, the better the temperature resistance.
1.4 Salt resistance test of mixture solution
Take a certain amount of hydroxypropyl methylcellulose and carboxymethyl starch dried at 105°C for 2 h, according to the mass ratio of 1:1, 1:3, 1:4, 1:5, 1:8 and 1: 9 Prepare a mixture, weigh it accurately (accurate to 1 mg), use 1% saline solution to prepare a 1% saline solution of the mixture, put it in an ice-water bath, stir until a certain viscosity is produced, let it stand for 3 hours, and store it at 20°C Measure the viscosity; compare the measured viscosity value with the viscosity value of the mixture solution prepared with distilled water, and pay attention to the change value; the test result can be expressed by salt-viscosity ratio (SVR).
2. Results and Discussion
2.1 Variation law of compound viscosity of mixture solution
As the amount of CMS added increases, the viscosity of the mixture solution increases. When the mass ratio of CMS to HPMC is about 1:3, the solution viscosity reaches the maximum and then decreases.
After adding CMS, the viscosity of the mixture increases obviously; after adding CMC, the viscosity of the compound sample has been decreasing, but it is not a simple addition of viscosity, because the viscosity of CMC itself is very low, and after compounding with HPMC, there is also a synergistic viscosity increase effect , just not as obvious as CMS. In addition, it was found during the dissolution process that the dissolution rate and dissolution quality of the mixture added with CMS were much better than those with CMC added. And by observation, the light transmittance of the CMS mixture is also better than that of the CMC mixture, which also shows from another perspective that the solubility of the CMS mixture is better than that of the CMC mixture.
From a structural point of view, the similarities between CMC and CMS are that both are ionic polysaccharides, both belong to polyanionic polymers, and both contain a certain number of carboxymethyl groups, but the difference is that the two are in the link of the unit ring. One is β-1,4-glycosidic linkage (CMC), and the other is α-1,4-glycosidic linkage (CMS).
First of all, CMC and HPMC are both cellulose derivatives, the structure of the molecular chain is similar, and they are all connected by β-1,4-glucosidic bonds. The difference is that CMC is an anionic cellulose, which is an ionic type. Ether, while HPMC is a non-ionic ether. Because of this similar chain structure, macromolecules attract each other, complement each other, and intertwine with each other, which plays a certain role in increasing viscosity. The biggest difference between CMS and cellulose is the connection of glucose residues. CMS is composed of D-glucose residues connected by α-1,4-glycosidic bonds, while CMC is composed of D-glucose residues connected by β-1 , formed by 4-glycosidic linkages. Starch chains are more rigid due to the arrangement of the surrounding electron cloud. At the same time, the starch also contains a branched chain structure, which intertwines with HPMC to lock more water and increase the viscosity of the compound sample.
When the compound ratio of CMS and HPMC is about 1:3 (mass ratio), there is a maximum viscosity value, which may be due to the relationship between the carboxymethyl group and the hydroxyl, hydroxypropyl, and methoxy groups in starch There is a best compounding ratio, which makes the viscosity the largest, and when this ratio is exceeded, the viscosity begins to decrease.
2.2 Temperature resistance of the mixture solution
The slope of the straight line of the sample with the compound ratio of CMS/HPMC of 1:3 is the largest, while the slope of the straight line of the CMC sample is the smallest. This shows that the temperature resistance of the CMC sample is the best. And the compound sample of CMC and HPMC has better temperature resistance than the compound sample of CMS and HPMC. The slope of the sample with a CMS/HPMC compound ratio of 1:1 is smaller than that of the sample with a CMS/HPMC compound ratio of 1:3. It can be seen that increasing the CMS content can improve the temperature resistance of the sample. Since HPMC has a gel temperature, the solubility will decrease with the increase of temperature. When the temperature reaches the gel temperature of about 60°C, HPMC begins to swell, and the solution begins to turn milky white. At this time, the viscosity reaches a critical value.
When the temperature reaches 70°C, HPMC has basically swelled, and the slope of the pure HPMC curve is 0, but only CMS plays a role in the viscosity of the CMS/HPMC compound solution. CMS is an ionic starch ether, which can be dissolved in both cold water and hot water, so the temperature has little effect on its solubility, because in the sample with a compound ratio of 1:1, the amount of CMS is higher than that of the sample with a ratio of 1:3 There are many in it, so its temperature resistance is better than the sample with a compound ratio of 1:3.
2.3 Salt resistance of the mixture solution
With the increase of CMS and CMC addition, the salt tolerance of the samples gradually decreased. Because CMS and CMC are ionic ethers, charged groups are formed due to hydrolysis in the solution. The charge shielding effect of the inorganic salt on the charged group weakens the electrostatic repulsion along the macromolecular chain extension, and the extension of the macromolecular chain is limited at this time. At the same time, in the salt solution, the dehydration of the inorganic salt causes the hydration of the macromolecular chain to be weakened, and the hydration of the hydration group is limited to a certain extent, so the macromolecular chain shrinks and curls, and the viscosity decreases. The viscosity of CMS and CMC decreases with the increase of salt concentration. In the mixture, with the increase of the addition of CMS and CMC, the viscosity will decrease in the same salt solution, and the salt-to-viscosity ratio will decrease.
The viscosity of the mixture solution increases with the addition of CMS and CMC, and it is close to the maximum viscosity when the compounding ratio is 1:3. related. CMS has a viscosifying effect on HPMC, and the effect is more obvious than that of CMC. When the ratio of CMS/HPMC was 1:1, the viscosity of the solution began to decrease, but the viscosity of the solution was still greater than that of a single HPMC solution.
Compared with CMC, low-viscosity CMS can increase the viscosity of HPMC, and it is stronger than the mixture of CMC and HPMC in terms of dissolution rate, dissolution quality and light transmittance of the mixture.
CMS can improve the temperature resistance of HPMC, but because CMS is an ionic starch ether, the salt tolerance of the mixture decreases with the increase of CMS addition.