Quality identification of HPMC

At present, the quality and price of HPMC in China are different, which makes it difficult for customers to make a correct choice. The modified HPMC made by TongWai company is the result of many years' research. Adding trace substances can improve the construction performance and operability. Of course, it will affect some other properties, but generally speaking, it is highly efficient. The only purpose of HPMC made by domestic manufacturers is to reduce the cost and greatly reduce the water retention and adhesion properties of products, resulting in many construction projects Construction quality problems.

The differences between pure HPMC and adulterated HPMC are as follows:

1. The pure HPMC is fluffy in visual state, and the packing density is small, with the range of 0.3-0.4g/ml; the adulterated HPMC has better fluidity and heavier hand feeling, which is obviously different from the original appearance.

2. Pure HPMC aqueous solution is clear, with high transmittance, and water retention rate ≥ 97%; adulterated HPMC aqueous solution is turbid, and the 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 flavor, even if it is tasteless, it will feel heavy.

4. Pure HPMC powder is fibrous under microscope or magnifying glass, and granular solid or crystal can be observed in adulterated HPMC under microscope or magnifying glass.

200000 insurmountable height?

Many domestic experts and scholars have published papers that the production of HPMC is restricted by domestic equipment safety and sealing, slurry process and low-pressure production, and ordinary enterprises can not produce products with viscosity above 200000. In summer, we can't even produce products with viscosity above 80000. They believe that the so-called 200000 products must be fake products.

The expert's argument is not unreasonable, according to the domestic production situation before, can really draw the above conclusion.

The key to improve the viscosity of HPMC is the high sealing of reactor, high pressure reaction and high quality raw materials. The high sealing property avoids the degradation of cellulose by oxygen, and the high pressure reaction conditions promote the penetration of etherifying agent into cellulose and ensure the product uniformity.

The basic indexes of 200 000 cps HPMC were as follows

The viscosity of 2% aqueous solution is 200000cps

Product purity ≥ 98%

Methoxy content 19-24%

Hydroxypropoxy content: 4-12%

The characteristics of 200 000 cps HPMC are as follows

1. Excellent water retention and thickening performance to ensure complete hydration of slurry.

2. High bond strength and significant air entraining effect can effectively restrain shrinkage and cracking.

3. Delay the heat release of cement hydration, delay the setting time and control the workable time of cement mortar.

4. Improve the water consistency of the pumped mortar, improve the rheological property, and prevent segregation and bleeding.

5. Special products, in view of the high temperature construction environment in summer, to ensure the slurry efficient hydration and no stratification.

Due to the lax market supervision and the increasingly fierce competition in the mortar industry, some businesses, in order to cater to the market, mix a large number of low-cost materials to produce cheap cellulose ether. Here, the editor has the obligation to remind customers not to blindly pursue low prices, so as to avoid being cheated and lead to engineering accidents, and ultimately the gains outweigh the losses.

Common adulteration methods and identification methods:

(1) The viscosity of cellulose ether solution can be increased rapidly by adding amide cellulose ether, which can not be identified by viscometer.

Identification method: due to the properties of amides, the cellulose ether solution often has the phenomenon of drawing, but good cellulose ether will not appear after dissolution. The solution is like jelly, so-called sticky but not connected.

(2) Cellulose ether added with starch. Starch is generally insoluble in water, and the solution is often poor in light transmittance.

Identification method: iodine was added into cellulose ether solution, and starch could be considered to be added if the color turned blue.

(3) Add polyvinyl alcohol powder. It is well known that the market price of polyvinyl alcohol powder such as 2488 and 1788 is often lower than that of cellulose ether. The cost of cellulose ether can be reduced by mixing polyvinyl alcohol powder.

In this way, the density of cellulose is higher than that of ether. If the solution is dissolved rapidly with water and the solution is picked with a glass rod, the wire drawing phenomenon will be obvious.

Conclusion: due to its special structure and group, the water retention of cellulose ether can not be replaced by other materials. No matter what kind of filler is added, as long as it is mixed in a large amount, its water retention will be greatly reduced. The content of HPMC with normal 10W viscosity is 0.15 ~ 0.2 ‰ in ordinary mortar, and the water retention rate is more than 88%, and the water retention rate of poor quality cellulose ether added to 0.3 ‰ may not reach 88%, and the bleeding of mortar is often serious. Therefore, the water retention rate is an important index to measure the quality of HPMC, whether it is good or bad, as long as it is added into the mortar, it will be clear at a glance.