hydroxypropyl methylcellulose HPMC in Plastering MortarFebruary 2nd 2023
Redispersible polymer powder can improve the bending strength and adhesion strength of the mortar because it can form a polymer film on the surface of the mortar particles, and there are pores on part of the surface of the film, and the pore surface is filled with the mortar, which reduces the stress concentration. And under the action of external force, it will relax without breaking.
The mortar forms a rigid skeleton after the cement is hydrated, and the polymer in the skeleton acts as a movable joint, similar to the tissue of the human body. The membrane formed by the polymer can be compared to joints and ligaments to ensure the elasticity and toughness of the rigid skeleton.
In the polymer-modified cement mortar system, the continuous and complete polymer film is interwoven with the cement paste and sand particles to make the whole mortar denser. At the same time, the whole is filled with capillaries and cavities to make the whole a flexible network. Therefore, the polymer membrane can effectively transmit pressure and elastic tension.
The polymer film can bridge the shrinkage cracks at the polymer-mortar interface, heal the shrinkage cracks, and improve the sealing and cohesive strength of the mortar. Among them, the presence of highly flexible and highly elastic polymer regions improves the flexibility and elasticity of the mortar, and provides cohesion and dynamic behavior for the rigid skeleton.
When an external force is applied, due to the improvement of flexibility and elasticity, the propagation of micro-cracks will be delayed until a higher stress is reached. The interwoven polymer regions also play a certain role in preventing micro-cracks from merging into through-cracks. Therefore, the redispersible polymer powder increases the failure stress and failure strain of the material.
The redispersible polymer powder has good redispersibility. When it comes into contact with water, it redisperses into an emulsion, and its chemical properties are almost the same as the initial emulsion. Adding dispersible emulsion polymer powder to cement or gypsum-based dry powder ready-mixed mortar can improve the various properties of the mortar, such as: improving the material’s cohesive force and cohesive force; reducing the water absorption of the material and the elastic modulus of the material; strengthening the material flexural strength, impact resistance, abrasion resistance and durability; improve the construction performance of materials, etc.