HPMC For Cement Mortar
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Faq
What is the main function of HPMC in putty powder and does it undergo a chemical reaction?
HPMC can be divided into two types: instant soluble and heat soluble. Instant soluble HPMC quickly disperses in cold water, disappearing in the water. At this stage, the liquid does not have viscosity because HPMC is only dispersed in the water and not completely dissolved. After about 2 minutes, the viscosity of the liquid gradually increases, forming a transparent and viscous colloidal solution. Heat soluble HPMC tends to agglomerate in cold water but can rapidly disperse in hot water, disappearing in it. As the temperature decreases to a certain point, viscosity slowly appears until a transparent and viscous colloidal solution is formed. Heat soluble HPMC can only be used in putty powder and mortar, as it tends to agglomerate in liquid adhesives and coatings and cannot be used effectively. Instant soluble HPMC has a wider range of applications and can be used in putty powder, mortar, liquid adhesives, and coatings without any restrictions.
Why does hydroxypropyl methylcellulose (HPMC) have an odor?
For putty powder, a viscosity of around 100,000 is generally sufficient, while mortar requires a higher viscosity, around 150,000, to be effective. Moreover, the most important function of HPMC is water retention, followed by thickening. In putty powder, as long as it has good water retention and a lower viscosity (70,000-80,000), it can still be used. Of course, a higher viscosity provides relatively better water retention. However, when the viscosity exceeds 100,000, the impact of viscosity on water retention becomes less significant.
How many types does 2-Hydroxypropyl methylcellulose (HPMC) have, and what are the differences in their applications?
In the application of HPMC in putty powder, it plays three roles: thickening, water retention, and facilitating construction. Thickening: Cellulose can thicken the mixture, maintain uniform suspension, and prevent sagging. Water retention: It slows down the drying process of putty powder and assists in the reaction of lime and calcium in water. Construction: Cellulose acts as a lubricant, improving the workability of the putty powder. HPMC does not participate in any chemical reactions; it only serves as an auxiliary agent. When putty powder is mixed with water and applied to the wall, a chemical reaction occurs because new substances are formed. However, if the putty powder is scraped off the wall, ground into powder, and reused, it is not suitable because a new substance (calcium carbonate) has already formed. The main components of lime and calcium powder are Ca(OH)2, CaO, and a small amount of CaCO3. The reaction can be represented as: CaO + H2O = Ca(OH)2 — Ca(OH)2 + CO2 = CaCO3 ↓ + H2O. Under the action of water and carbon dioxide in the air, lime and calcium carbonate are formed. HPMC only assists in water retention and the better reaction of lime and calcium; it does not participate in any reactions itself.
What is the dosage of Hydroxypropyl Methylcellulose (HPMC) in putty powder?
The two main indicators most users are concerned about are the content of hydroxypropyl and viscosity. Higher hydroxypropyl content generally indicates better water retention. A higher viscosity also provides relatively better water retention (not absolute), and HPMC with higher viscosity is more suitable for cement mortar.