What are the properties of carboxymethyl cellulose?

Answer: Carboxymethyl cellulose also has different properties due to its different degrees of substitution. The degree of substitution, also known as the degree of etherification, means the average number of H in the three OH hydroxyl groups replaced by CH2COONa. When the three hydroxyl groups on the cellulose-based ring have 0.4 H in the hydroxyl group replaced by carboxymethyl, it can be dissolved in water. At this time, it is called 0.4 substitution degree or medium substitution degree (substitution degree 0.4-1.2) .

Properties of carboxymethyl cellulose:

(1) It is white powder (or coarse grain, fibrous), tasteless, harmless, easily soluble in water, and forms a transparent sticky shape, and the solution is neutral or slightly alkaline. It has good dispersion and binding power.

(2) Its aqueous solution can be used as an emulsifier of oil/water type and water/oil type. It also has emulsifying ability for oil and wax, and is a strong emulsifier.

(3) When the solution encounters heavy metal salts such as lead acetate, ferric chloride, silver nitrate, stannous chloride, and potassium dichromate, precipitation can occur. However, except for lead acetate, it can still be re-dissolved in sodium hydroxide solution, and the precipitates such as barium, iron and aluminum are easily soluble in 1% ammonium hydroxide solution.

(4) When the solution encounters organic acid and inorganic acid solution, precipitation can occur. According to the observation, when the pH value is 2.5, turbidity and precipitation have begun. Therefore pH 2.5 can be considered as the critical point.

(5) For salts such as calcium, magnesium and table salt, no precipitation will occur, but the viscosity should be reduced, such as adding EDTA or phosphate and other substances to prevent it.

(6) Temperature has a great influence on the viscosity of its aqueous solution. The viscosity decreases correspondingly when the temperature rises, and vice versa. The stability of the viscosity of the aqueous solution at room temperature remains unchanged, but the viscosity can gradually decrease when heated above 80°C for a long time. Generally, when the temperature does not exceed 110°C, even if the temperature is maintained for 3 hours, and then cooled to 25°C, the viscosity still returns to its original state; but when the temperature is heated to 120°C for 2 hours, although the temperature is restored, the viscosity drops by 18.9%. .

(7) The pH value will also have a certain influence on the viscosity of its aqueous solution. Generally, when the pH of a low-viscosity solution deviates from neutral, its viscosity has little effect, while for a medium-viscosity solution, if its pH deviates from neutral, the viscosity begins to decrease gradually; if the pH of a high-viscosity solution deviates from neutral, its viscosity will decrease. A sharp decline.

(8) Compatible with other water-soluble glues, softeners and resins. For example, it is compatible with animal glue, gum arabic, glycerin and soluble starch. It is also compatible with water glass, polyvinyl alcohol, urea-formaldehyde resin, melamine-formaldehyde resin, etc., but to a lesser degree.

(9) The film made by irradiating ultraviolet light for 100 hours still has no discoloration or brittleness.

(10) There are three viscosity ranges to choose from according to the application. For gypsum, use medium viscosity (2% aqueous solution at 300-600mPa·s), if you choose high viscosity (1% solution at 2000mPa·s or more), you can use it in the dosage should be appropriately lowered.

(11) Its aqueous solution acts as a retarder in gypsum.

(12) Bacteria and microorganisms have no obvious effect on its powder form, but they have an effect on its aqueous solution. After contamination, the viscosity will drop and mildew will appear. Adding an appropriate amount of preservatives in advance can maintain its viscosity and prevent mildew for a long time. Available preservatives are: BIT (1.2-benzisothiazolin-3-one), racebendazim, thiram, chlorothalonil, etc. The reference addition amount in the aqueous solution is 0.05% to 0.1%.

How effective is hydroxypropyl methylcellulose as a water-retaining agent for anhydrite binder?

Answer: Hydroxypropyl methylcellulose is a high-efficiency water-retaining agent for gypsum cementitious materials. With the increase of the content of hydroxypropyl methylcellulose. The water retention of gypsum cemented material increases rapidly. When no water retaining agent is added, the water retention rate of gypsum cemented material is about 68%. When the amount of water retaining agent is 0.15%, the water retention rate of gypsum cemented material can reach 90.5%. And the water retention requirements of the bottom plaster. The dosage of water-retaining agent exceeds 0.2%, further increase the dosage, and the water retention rate of gypsum cementitious material increases slowly. Preparation of anhydrite plastering materials. The suitable dosage of hydroxypropyl methylcellulose is 0.1%-0.15%.

What are the different effects of different cellulose on plaster of paris?

Answer: Both carboxymethyl cellulose and methyl cellulose can be used as water-retaining agents for plaster of paris, but the water-retaining effect of carboxymethyl cellulose is much lower than that of methyl cellulose, and carboxymethyl cellulose contains sodium salt, so it is suitable for Plaster of Paris has a retarding effect and reduces the strength of the plaster. Methyl cellulose is an ideal admixture for gypsum cementitious materials integrating water retention, thickening, strengthening, and viscosifying, except that some varieties have a retarding effect when the dosage is large. higher than carboxymethyl cellulose. For this reason, most gypsum composite gelling materials adopt the method of compounding carboxymethyl cellulose and methyl cellulose, which not only exert their respective characteristics (such as the retarding effect of carboxymethyl cellulose, the reinforcing effect of methyl cellulose ), and exert their common advantages (such as their water retention and thickening effect). In this way, both the water retention performance of the gypsum cementitious material and the comprehensive performance of the gypsum cementitious material can be improved, while the cost increase is kept at the lowest point.