Application characteristics of hydroxypropyl methylcellulose in putty powder
The application characteristics and precautions of hydroxypropyl methylcellulose in putty powder are briefly introduced.
In the putty powder, hydroxypropyl methyl cellulose plays three functions: thickening, water retention and construction.
1. Thickening: Cellulose can thicken to suspend, keep the solution uniform and consistent, and resist sagging.
2. Water retention: Make the putty powder dry slowly, and assist the reaction of lime calcium under the action of water.
3. Construction: Cellulose has lubricating effect, which can make putty powder have good construction.
How to choose its viscosity when producing putty powder, hydroxypropyl methylcellulose with a viscosity of 100,000 is generally enough in putty powder, and the requirements in mortar are higher, and HPMC with a viscosity of 150,000 is easy to use. Moreover, the most important role of hydroxypropyl methylcellulose HPMC is to retain water, followed by thickening. In putty powder, as long as the water retention is good and the viscosity is lower (70,000-80,000), it is also possible. Of course, the viscosity is higher, and the relative water retention is better. When the viscosity of hydroxypropyl methylcellulose exceeds 100,000, Viscosity has little effect on water retention.
Hydroxypropyl methylcellulose HPMC does not participate in any chemical reaction and only plays an auxiliary role. Adding water to the putty powder and putting it on the wall is a chemical reaction. Because of the formation of new substances, take the putty powder on the wall off the wall, grind it into powder, and use it again. It will not work, because new substances (calcium carbonate) have been formed. ) up. 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 in water and air Under the action of CO2, calcium carbonate is generated, while HPMC only retains water and assists the better reaction of ash calcium, and does not participate in any reaction itself.
The types of putty powder are: special putty for interior walls, special putty for interior walls, water-resistant putty for interior walls, water-mixed paint putty, high-elasticity patching putty, high-elasticity putty for exterior walls, flexible putty for exterior walls, anti-cracking putty for exterior walls, and putty for exterior walls. Wall tile putty, exterior wall fluorocarbon paint putty, furniture putty, putty paste, etc.
The selection points of putty are as follows:
Water-resistant putty is suitable for all indoor walls, basements, toilets and bathrooms and other damp engineering parts, as well as water-resistant scraping wall putty for initial residential decoration; it is not suitable for walls made of soft materials such as metal products, paper products, fabrics and polystyrene.
2. General putty is used in places that do not require water resistance; water-resistant putty is used in places that require water resistance and high bonding strength.
3. It is suitable for cement mortar plastering, mixed mortar plastering, concrete, gypsum board, decorative mortar, clay bricks and other new and old wall bases, so that it has good water resistance and air permeability. In the finishing project, it should be used together with the building interior wall paint.
4. The water-resistant putty is used on the inner side of the outer wall and in the interior walls of the kitchen and bathroom, etc., the class I products can be used; when the project is in a humid environment, such as basements, toilets and bathrooms, class II products should be preferred.
5. Putty is used for tile veneer, and the linear shrinkage index should be increased to avoid the tiles from being pulled and cracked. The line shrinkage value should be less than 1%.
6. The volatile organic compound (VOC) value should be less than 125g/L (tested according to GB 18582-2001 standard).
In the production of putty powder, customers generally choose hydroxypropyl methyl cellulose with a viscosity of 100,000. The cellulose with a viscosity of 100,000 has good water retention, which is very good in the construction of putty powder and easy to scrape.