hydroxypropyl methylcellulose HPMC in Plastering MortarFebruary 2nd 2023
1. basic concept
Redispersible polymer powder is the main additive for dry powder ready-mixed mortar such as cement-based or gypsum-based.
Redispersible latex powder is a polymer emulsion that is spray-dried and aggregated from the initial 2um to form spherical particles of 80~120um. Because the surfaces of the particles are coated with an inorganic, hard-structure-resistant powder, we obtain dry polymer powders. They are extremely easy to pour and bag for storage in warehouses. When the powder is mixed with water, cement or gypsum-based mortar, it can be redispersed, and the basic particles (2um) in it will re-form into a state equivalent to the original latex, so it is called redispersible latex powder.
It has good redispersibility, re-disperses into an emulsion on contact with water, and has the exact same chemical properties as the original emulsion. By adding dispersible polymer powder to cement-based or gypsum-based dry powder ready-mixed mortar, various properties of the mortar can be improved, such as:
Improve the adhesion and cohesion of mortar;
Reduce the water absorption of the material and the elastic modulus of the material;
Flexural strength, impact resistance, abrasion resistance and durability of reinforcement materials;
Improve the construction performance of materials, etc.
2. Types of dispersible polymer powders
At present, the main applications in the market can be divided into disperse latex:
Vinyl acetate and ethylene copolymer rubber powder (Vac/E), ethylene and vinyl chloride and vinyl laurate ternary copolymer rubber powder (E/Vc/VL), vinyl acetate and ethylene and higher fatty acid vinyl ester terpolymerization Rubber powder (Vac/E/VeoVa), vinyl acetate and higher fatty acid vinyl ester copolymer rubber powder (Vac/VeoVa), acrylate and styrene copolymer rubber powder (A/S), vinyl acetate and acrylate and higher fatty acid Vinyl ester terpolymer rubber powder (Vac/A/VeoVa), vinyl acetate homopolymer rubber powder (PVac), styrene and butadiene copolymer rubber powder (SBR), etc.
3. The composition of dispersible polymer powder
Dispersible polymer powders are usually white powders, but a few have other colors. Its ingredients include:
Polymer resin: It is located in the core part of the rubber powder particles, and it is also the main component of the redispersible polymer powder.
Additive (internal): together with the resin, it plays the role of modifying the resin.
Additives (external): Additional materials are added to further expand the performance of the dispersible polymer powder.
Anti-caking agent: fine mineral filler, mainly used to prevent the rubber powder from caking during storage and transportation and to facilitate the flow of the rubber powder (dumping from paper bags or tankers).
4. The role of dispersible polymer powder in mortar
The redispersible latex powder is dispersed into a film and acts as a reinforcing agent as the second adhesive;
The protective colloid is absorbed by the mortar system (it will not be destroyed by water after film formation, or “secondary dispersion”;
The film-forming polymer resin is distributed throughout the mortar system as a reinforcing material, thereby increasing the cohesion of the mortar;
5. The role of dispersible polymer powder in wet mortar:
Improve construction performance;
Improve flow properties;
Increase thixotropy and sag resistance;