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The quality of hydroxypropyl methyl cellulose is good and bad

January 4, 2022by admin0

Speaking of hydroxypropyl methylcellulose, people first think of putty powder, mortar, tile glue, etc. Hydroxypropyl methylcellulose as an additive for putty powder, mortar, tile glue can improve construction performance and improve workability. However, some manufacturers add a large amount of other ingredients in order to reduce costs, which greatly reduces the water retention and adhesion of their products. Let’s take a look at the difference between inferior hydroxypropyl methylcellulose and pure hydroxypropyl methylcellulose. .

1. The pure HPMC is fluffy and has a small bulk density in the range of 0.3-0.4g/ml; the adulterated HPMC has better fluidity and feels heavier, which is obviously different from the original appearance.
2. Pure HPMC should not smell the taste of ammonia, starch and alcohol; adulterated HPMC can often smell various tastes, even if it is tasteless, it will feel heavy.
3. The pure HPMC aqueous solution is clear, has high light transmittance, and the water retention rate is ≥97%; the adulterated HPMC aqueous solution is turbid, and the water retention rate is difficult to reach 80%.
4. The pure HPMC powder is fibrous under a microscope or magnifying glass; the adulterated HPMC can be observed in granular solids or crystals under a microscope or magnifying glass.
5. Look at the number of cellulose mesh, color and impurities: mesh (thickness) 80-120 meshes in various specifications, 80 mesh cellulose is mostly the finer the better, the particles are uniform, the color is white, the whiter the better, pay attention to bleaching the fiber Vegetarian deceptive.
6. The specific gravity of cellulose soluble in water. The greater the specific gravity, the better the quality of the cellulose. The experimental method is to put two water-soluble cellulose comparison samples into the same float. The greater the buoyancy, the better the quality.
7. Dissolve in water at a ratio of 1 to 10, and check the transparency under light. The more transparent the better, and the turbidity is a defective product.
8. Although the whiteness cannot determine whether the hydroxypropyl methyl cellulose is easy to use, and if a brightener is added in the production process, it will affect its quality. However, most good products have good whiteness.

Common adulteration methods and identification methods:

1. Adding amide cellulose ether can make the solution viscosity of cellulose ether increase rapidly, making it impossible to identify with a viscometer.
Identification method: Due to the characteristics of amides, this kind of cellulose ether solution tends to show the phenomenon of stringing, but after the dissolution of a good cellulose ether, there will be no stringing phenomenon. The solution is like jelly, so-called stickiness.

2. Add the cellulose ether of starch. Starch is generally insoluble in water, and the solution often has poor light transmittance.
Identification method: Drop iodine into the cellulose ether solution. If the color turns blue, it can be considered that starch has been added.

3. Add polyvinyl alcohol powder. As we all know, the market price of polyvinyl alcohol powder such as 2488 and 1788 is often lower than that of cellulose ether. Mixing polyvinyl alcohol powder can reduce the cost of cellulose ether.
Identification method: This kind of cellulose ether is often granular and dense. It dissolves quickly with water. Pick the solution with a glass rod, and there will be more obvious wire drawing.

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