HPMC can be divided into construction grade, food grade and pharmaceutical grade according to the purpose. At present, most of the domestic products are construction grades, and in the construction grades, the amount of putty powder is very large. Mix HPMC powder with a large amount of other powdery substances, mix them thoroughly with a mixer, and then add water to dissolve, then HPMC can be dissolved at this time without agglomeration, because every tiny corner, a little bit of HPMC powder, meets water. will dissolve immediately. Putty powder and mortar manufacturers mostly use this method. Hydroxypropyl methylcellulose (HPMC) is used as a thickener and water retention agent in putty powder mortar.
The gel temperature of HPMC is related to its methoxy content, the lower the methoxy content ↓, the higher the gel temperature ↑. The cold water instant type of HPMC is surface-treated with glyoxal, and it disperses quickly in cold water, but it does not really dissolve. It only dissolves when the viscosity increases. Hot melt types are not surface treated with glyoxal. If the amount of glyoxal is large, the dispersion will be fast, but the viscosity will increase slowly, and if the amount is small, the opposite will be true. HPMC can be divided into instant type and hot-dissolution type. The instant type product disperses quickly in cold water and disappears into the water. At this time, the liquid has no viscosity because HPMC is only dispersed in water without real dissolution. About 2 minutes, the viscosity of the liquid gradually increases, forming a transparent viscous colloid. Hot-melt products, when met with cold water, can disperse quickly in hot water and disappear in hot water. When the temperature drops to a certain temperature, the viscosity will slowly appear until it forms a transparent viscous colloid. The hot-melt type can only be used in putty powder and mortar. In liquid glue and paint, there will be grouping phenomenon and cannot be used. The instant type has a wider range of applications. It can be used in putty powder and mortar, as well as liquid glue and paint, without any contraindications.
The HPMC produced by the solvent method uses toluene and isopropanol as solvents. If the washing is not very good, there will be some residual smell. Application of putty powder: the requirements are low, the viscosity is 100,000, it is enough, the important thing is to keep water well. Application of mortar: higher requirements, high viscosity, 150,000 is better. Application of glue: instant products with high viscosity are required. The amount of HPMC used in practical applications varies depending on the climate environment, temperature, local ash calcium quality, putty powder formula and “quality required by customers”. The viscosity of hydroxypropyl methylcellulose (HPMC)-putty powder is generally 100,000, and the requirement for mortar is higher, and it needs 150,000 to be easy to use. Moreover, the main function of HPMC is water retention, followed by thickening. In the putty powder, as long as the water retention is good and the viscosity is low (70,000-80,000), it is also possible. Of course, the higher the viscosity, the better the relative water retention. When the viscosity exceeds 100,000, the viscosity will affect the water retention. Not too much; those with high hydroxypropyl content generally have better water retention. The one with high viscosity has relatively better water retention, and the one with high viscosity is better used in cement mortar.
In putty powder, HPMC plays three roles of thickening, water retention and construction. Do not participate in any reactions. The reason for the bubbles may be that too much water is put in, or it may be that the bottom layer is not dry, and another layer is scraped on top, and it is easy to foam. Thickening effect of HPMC in putty powder: cellulose can be thickened to suspend, keep the solution uniform and consistent, and resist sagging. The water retention effect of HPMC in putty powder: make the putty powder dry slowly, and assist ash calcium to react under the action of water. The construction effect of HPMC in putty powder: cellulose has a lubricating effect, which can make putty powder have good construction. HPMC does not participate in any chemical reactions, but only plays an auxiliary role.
The powder loss of putty powder is mainly related to the quality of ash calcium, and has little to do with HPMC. The low calcium content of gray calcium and the improper ratio of CaO and Ca(OH)2 in gray calcium will cause powder loss. If it has something to do with HPMC, then if the water retention of HPMC is poor, it will also cause the powder to fall off. Adding water to the putty powder and putting it on the wall is a chemical reaction, because new substances are formed, and the putty powder on the wall is removed from the wall. Down, ground into powder, and reuse, it will not work, because new substances (calcium carbonate) have been formed. The main components of ash calcium powder are: a mixture of Ca(OH)2, CaO and a small amount of CaCO3, CaO+H2O=Ca(OH)2—Ca(OH)2+CO2=CaCO3↓+H2O Ash calcium is in water and air Under the action of CO2, calcium carbonate is generated, while HPMC only retains water, assisting the better reaction of ash calcium, and does not participate in any reaction itself.
Post time: Mar-18-2023