There are the following differences between pure HPMC and adulterated HPMC:
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. The pure HPMC aqueous solution is clear, has high light transmittance, and the water retention rate is ≥97%; the adulterated HPMC water solution is turbid, and the water retention rate is difficult to reach 80%.
3. Pure HPMC should not smell ammonia, starch and alcohol; adulterated HPMC can often smell various tastes, even if it is tasteless, it will feel heavy.
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.
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 wire drawing, while a good cellulose ether does not show wire drawing after being dissolved. The solution is like jelly, so-called stickiness and non-connection.
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.