Authenticity of hydroxypropyl methylcellulose (HPMC)?

Update:03-01-2020
Summary:

Now with the country's requirements for building energy […]

Now with the country's requirements for building energy conservation and environmental protection, the construction additive hydroxypropyl methylcellulose has gained the trust of more and more builders. At present, the quality of hydroxypropyl methylcellulose in China is uneven, and the prices are different. The disparity has caused the product's water retention and adhesion properties to be greatly reduced, causing many building quality problems, making it difficult for customers to make the right choice.
There are the following differences between pure HPMC and adulterated HPMC:
1. Pure HPMC has a fluffy visual state and a small bulk density, ranging from 0.3-0.4g / ml; adulterated HPMC has better fluidity and heavier feel, which is significantly different from the original appearance.
2. Pure HPMC aqueous solution is clear, high light transmittance, water retention rate ≥97%; adulterated HPMC aqueous solution is cloudy, and water retention rate is difficult to reach 80%.
3. Pure HPMC should not smell the smell of ammonia, starch and alcohol; adulterated HPMC can often smell all kinds of taste, even if it is tasteless, it will feel heavy.
4. Pure HPMC powder is fibrous under a microscope or magnifier; adulterated HPMC can observe granular solids or crystals under a microscope or magnifier.
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 cellulose ether solution tends to have stringing phenomenon, and good cellulose ether does not have stringing after dissolution. The solution is like jelly, so-called sticky but not connected.
2. Add starch cellulose ether. Starch is generally insoluble in water, and solutions often have poor light transmission.
Identification method: The cellulose ether solution was dripped with iodine, and the color turned blue.
3. Add polyvinyl alcohol powder. As we all know, the market price of polyvinyl alcohol powders such as 2488 and 1788 is often lower than cellulose ether, and mixing polyvinyl alcohol powder can reduce the cost of cellulose ether.
Identification method: This cellulose ether is often granular and has a high density. Quickly dissolve with water, pick the solution with a glass rod, there will be obvious stringing phenomenon.
to sum up:
Because of its special structure and group, cellulose ether cannot retain the water retention of other substances. No matter what kind of filler is incorporated, as long as it is incorporated in a large amount, its water retention will be greatly reduced. The normal 10W viscosity of HPMC in ordinary mortar is 0.15 ~ 0.2 ‰, and the water retention rate is> 88%. It is not a problem, and the inferior cellulose ether may not reach 88% when it is added to 0.3 ‰. Mortar often Bleeding is severe. Therefore, the water retention rate is an important indicator of HPMC's pros and cons, whether it is good or bad, as long as it is added to the mortar, it will be clear at a glance.

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