one. The difference between adulterated hydroxypropyl methylcellulose (HPMC) and pure hydroxypropyl methylcellulose (HPMC)
1. Appearance: Pure hydroxypropyl methylcellulose HPMC looks fluffy and has a low bulk density, ranging from 0.3-0.4g/ml; adulterated hydroxypropyl methylcellulose HPMC has better fluidity and feels heavier , and there is a significant difference in appearance from the genuine product.
2. Status: Pure hydroxypropyl methylcellulose HPMC powder is fibrous under a microscope or magnifying glass; while adulterated hydroxypropyl methylcellulose HPMC can be observed as granular solids or crystals under a microscope or magnifying glass.
3. Odor: Pure hydroxypropyl methylcellulose HPMC can not smell the smell of ammonia, starch and alcohol; adulterated hydroxypropyl methylcellulose HPMC can smell all kinds of smells, even if it is tasteless, it will Feel heavy.
4. Aqueous solution: pure hydroxypropyl methylcellulose HPMC aqueous solution is clear, high light transmittance, water retention rate ≥ 97%; adulterated hydroxypropyl methylcellulose HPMC aqueous solution is turbid, and the water retention rate is difficult to reach 80%.
Second, the water retention of hydroxypropyl methylcellulose HPMC, distinguish the advantages and disadvantages:
The water retention of methyl cellulose ether under high temperature conditions is an important indicator to distinguish the quality of methyl cellulose ether. Factors such as air temperature, temperature and wind pressure speed will affect the volatilization rate of water in cement mortar and gypsum-based products. Therefore, in different seasons, there are some differences in the water retention effect of products with the same amount of HPMC added. In the specific construction, the water retention effect of the slurry can be adjusted by increasing or decreasing the amount of HPMC added. Excellent hydroxypropyl methylcellulose HPMC products can effectively solve the problem of water retention under high temperature.
High-quality methylcellulose can be uniformly and effectively dispersed in cement mortar and gypsum-based products, and wrap all solid particles, and form a wetting film, the moisture in the base is gradually released for a long time, and the inorganic The hydration reaction of the gelled material ensures the bond strength and compressive strength of the material. High-quality hydroxypropyl methylcellulose HPMC, its uniformity is very good, its methoxy and hydroxypropoxy groups are evenly distributed along the cellulose molecular chain, it can increase the oxygen on the hydroxyl and ether bonds The ability of atoms to associate with water to form hydrogen bonds turns free water into bound water, thereby effectively controlling water evaporation caused by high temperature weather and achieving high water retention.
Therefore, in high-temperature summer construction, in order to achieve the water retention effect, it is necessary to add high-quality HPMC products in sufficient quantities according to the formula, otherwise, there will be insufficient hydration, reduced strength, cracking, hollowing and shedding caused by excessive drying. problems, but also increase the construction difficulty of workers. As the temperature drops, the amount of water HPMC added can be gradually reduced, and the same water retention effect can be achieved.
3. Dissolution of hydroxypropyl methylcellulose HPMC
In the construction industry, hydroxypropyl methylcellulose HPMC is often put into neutral water, and the HPMC product is dissolved alone to judge the dissolution rate. After being placed in neutral water alone, the product that quickly clumps without dispersing is a product without surface treatment; after being placed in neutral water alone, the product that can disperse and not clump together is a product with surface treatment. When the surface untreated hydroxypropyl methylcellulose HPMC is dissolved alone, its single particle dissolves rapidly and forms a film quickly, causing water to no longer enter other particles, resulting in agglomeration and agglomeration, which is currently called slow dissolution in the market product.
Surface-treated hydroxypropyl methylcellulose HPMC product particles, in neutral water, individual particles can be dispersed without agglomeration, but the product viscosity will not immediately. After soaking for a certain period of time, the chemical structure of the surface treatment is destroyed, and the water can dissolve the HPMC particles. At this time, the product particles have been fully dispersed and absorbed enough water, so the product will not agglomerate or agglomerate after dissolution. Dispersion speed and dissolution speed depend on the degree of surface treatment. If the surface treatment is slight, the dispersion speed is relatively slow and the sticking speed is fast; while the product with deep surface treatment has fast dispersion speed and slow sticking speed. If you want to make this series of products dissolve quickly in this state, you can drop a small amount of alkaline substances when they are dissolved alone. The current market is usually referred to as instant products. The characteristics of surface-treated HPMC products are: in aqueous solution, the particles can disperse with each other, can dissolve quickly in alkaline state, and dissolve slowly in neutral and acidic state.
The characteristics of untreated hydroxypropyl methylcellulose HPMC are: a single particle dissolves very quickly in acidic, alkaline, and neutral states, but cannot disperse between particles in the liquid, resulting in clustering and agglomeration . In actual operation, after physical dispersion of this series of products and solid particles such as rubber powder, cement, sand, etc., the dissolution rate is very fast, and there is no agglomeration or agglomeration. When it is necessary to dissolve HPMC products separately, this series of products should be used with caution, as it will agglomerate and hold together. If it is necessary to dissolve the non-surface-treated hydroxypropyl methylcellulose HPMC product separately, it needs to be uniformly dispersed with 95°C hot water, and then cooled to dissolve.
In actual production operation, this series of products often dissolve after being dispersed with other solid particle materials under alkaline conditions, and its dissolution rate is no different from that of untreated products. It is also suitable for use in products that are dissolved alone, without caking or lumps. The specific model of the product can be selected according to the dissolution rate required by the construction.
During the construction process, whether it is cement mortar or gypsum-based slurry, most of them are alkaline systems, and the amount of HPMC added is very small, which can be evenly dispersed among these particles. When water is added, HPMC will quickly dissolve.
Post time: Dec-02-2022