At present, the quality of domestic hydroxypropyl methylcellulose varies greatly, and the price varies greatly, making it difficult for customers to make the right choice. The modified HPMC of the same foreign company is the result of many years of research. The addition of trace substances can improve the construction performance and improve the operability. Of course, it will affect some other properties, but generally speaking it is efficient; The only purpose of adding other ingredients is to reduce costs, resulting in greatly reduced water retention, cohesiveness and other properties of the product, resulting in many construction quality problems.
There are following differences between pure HPMC and adulterated HPMC:
1. Pure HPMC is visually fluffy and has a low bulk density, ranging from 0.3-0.4g/ml; adulterated HPMC has better fluidity and feels heavier, which is obviously different from the genuine product in appearance.
2. Pure HPMC aqueous solution is clear, high light transmittance, and water retention rate ≥ 97%; adulterated HPMC aqueous solution is cloudy, 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 all kinds of smells, even if it is tasteless, it will feel heavy.
4. Pure HPMC powder is fibrous under a microscope or magnifying glass; adulterated HPMC can be observed as granular solids or crystals under a microscope or magnifying glass.
An insurmountable height of 200,000?
Many domestic experts and scholars have published papers that believe that HPMC production is restricted by domestic equipment safety and sealing, slurry process and low-pressure production, and ordinary enterprises cannot produce products with a viscosity of more than 200,000. In summer, it is even impossible to produce products with a viscosity of more than 80,000. They believe that the so-called 200,000 products must be fake products.
The expert’s arguments are not unreasonable. According to the previous domestic production situation, the above conclusions can indeed be drawn.
The key to increasing the viscosity of HPMC is the high sealing of the reactor and high-pressure reaction as well as high-quality raw materials. The high airtightness prevents the degradation of cellulose by oxygen, and the high-pressure reaction condition promotes the penetration of the etherification agent into the cellulose and ensures the uniformity of the product.
The basic index of 200000cps hydroxypropyl methylcellulose:
2% aqueous solution viscosity 200000cps
Product purity ≥98%
Methoxy content 19-24%
Hydroxypropoxy content: 4-12%
200000cps hydroxypropyl methylcellulose features:
1. Excellent water retention and thickening properties to ensure complete hydration of the slurry.
2. High bonding strength and significant air-entraining effect, effectively inhibit shrinkage and cracking.
3. Delay the heat release of cement hydration, delay the setting time, and control the operable time of cement mortar.
4. Improve the water consistency of pumped mortar, improve rheology, and prevent segregation and bleeding.
5. Special products, aiming at the high temperature construction environment in summer, to ensure efficient hydration of the slurry without delamination.
Due to the lax market supervision, the competition in the mortar industry is becoming increasingly fierce. In order to cater to the market, some merchants have mixed a large amount of low-cost substances to produce cheap cellulose ether. Here, the editor is obliged to remind customers not to blindly pursue low prices, so as not to be fooled Be deceived, lead to engineering accidents, and ultimately the losses outweigh the gains.
Common adulteration methods and identification methods:
(1) The addition of amide to cellulose ether can rapidly increase the viscosity of the cellulose ether solution, making it impossible to identify it with a viscometer.
Identification method: Due to the characteristics of amides, this kind of cellulose ether solution often has stringing phenomenon, but good cellulose ether will not appear stringing phenomenon after dissolution, the solution is like jelly, so-called sticky but not connected.
(2) Add starch to cellulose ether. Starch is generally insoluble in water, and the solution often has poor light transmittance.
Identification method: Drop cellulose ether solution with iodine, 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, and mixing polyvinyl alcohol powder can reduce the cost of cellulose ether.
Identification method: This kind of cellulose ether is often granular and dense. Dissolves quickly with water, pick the solution with a glass rod, there will be a more obvious stringing phenomenon.
Summary: Due to its special structure and groups, the water retention of cellulose ether cannot be replaced by other substances. No matter what kind of filler is mixed in, as long as it is mixed in a large amount, its water retention will be greatly reduced. The amount of HPMC with a normal viscosity of 10W in the ordinary mortar is 0.15~0.2‰, and the water retention rate is >88%. Bleeding is more serious. Therefore, the water retention rate is an important indicator to measure the quality of HPMC, whether it is good or bad, as long as it is added to the mortar, it will be clear at a glance.
Post time: May-10-2023