The first step in producing a redispersible polymer powder is to produce a polymer dispersion, also known as an emulsion or latex. In this process, water-emulsified monomers (stabilized by emulsifiers or macromolecular protective colloids) react with initiators to initiate emulsion polymerization. Through this reaction, monomers are linked to form long-chain molecules (macromolecules), Namely polymers. During this reaction, monomer emulsion droplets transform into polymer “solid” particles. In such polymer emulsions, the stabilizers on the particle surfaces must prevent the latex from in any way coalescing and thus destabilizing. The mixture is then formulated for spray drying by adding different additives, and the addition of protective colloids and anti-caking agents allows the polymer to form a free-flowing powder that can be redispersed in water after spray drying.
The redispersible latex powder is distributed in the well-mixed dry powder mortar. After the mortar is mixed with water, the polymer powder is redispersed into the freshly mixed slurry and emulsified again; due to the hydration of the cement, surface evaporation and/or the absorption of the base layer, the internal pores are free The continuous consumption of water makes the latex particles dry to form a water-insoluble continuous film in water. This continuous film is formed by the fusion of single dispersed particles in the emulsion into a homogeneous body. In order to enable the redispersible latex powder to form a film in the hardened mortar, it must be ensured that the minimum film-forming temperature is lower than the curing temperature of the modified mortar.
The particle shape of the redispersible polymer powder and its film-forming properties after redispersion make it possible to have the following effects on the performance of the mortar in the fresh and hardened state:
1. Function in fresh mortar
◆ The “lubricating effect” of the particles makes the mortar mixture have good fluidity, so as to obtain better construction performance.
◆ The air-entraining effect makes the mortar compressible, making troweling easier.
◆ Adding different types of redispersible latex powder can obtain modified mortar with better plasticity or more viscous.
2. Function in hardened mortar
◆ The latex film can bridge the shrinkage cracks at the base-mortar interface and heal the shrinkage cracks.
◆ Improve the sealability of mortar.
◆ Improve the cohesive strength of mortar: the presence of highly flexible and highly elastic polymer regions improves the flexibility and elasticity of mortar,
Provides cohesive and dynamic behavior for rigid skeletons. When force is applied, due to the improved flexibility and elasticity the
Microcracks are delayed until higher stresses are reached.
◆ Interwoven polymer domains also hinder the coalescence of microcracks into penetrating cracks. Therefore, the redispersible polymer powder improves the failure stress and failure strain of the material.
It is necessary to add redispersible latex powder to dry cement mortar, because redispersible latex powder mainly has the following six advantages, and the following is an introduction for you.
1. Improve bonding strength and cohesion
Redispersible latex powder plays a great role in improving the bonding strength and cohesion of materials. Due to the penetration of polymer particles into the pores and capillaries of cement matrix, good cohesion is formed after hydration with cement. The polymer resin itself has excellent properties. It is more effective in improving the adhesion of cement mortar products to substrates, especially the poor adhesion of inorganic binders such as cement to organic substrates such as wood, fiber, PVC, and EPS.
2. Improve freeze-thaw stability and effectively prevent cracking of materials
Redispersible latex powder, the plasticity of its thermoplastic resin can overcome the damage caused by thermal expansion and contraction of cement mortar material caused by temperature difference. Overcoming the characteristics of large dry shrinkage and easy cracking of simple cement mortar, it can make the material flexible, thereby improving the long-term stability of the material.
3. Improve bending and tensile resistance
In the rigid skeleton formed after the cement mortar is hydrated, the polymer membrane is elastic and tough, and acts as a movable joint between the cement mortar particles, which can withstand high deformation loads and reduce the stress. Increased tensile and bending resistance.
4. Improve impact resistance
Redispersible latex powder is a thermoplastic resin. The soft film coated on the surface of mortar particles can absorb the impact of external force and relax without breaking, thus improving the impact resistance of mortar.
5. Improve hydrophobicity and reduce water absorption
Adding cocoa redispersible polymer powder can improve the microstructure of cement mortar. Its polymer forms an irreversible network during the cement hydration process, closes the capillary in the cement gel, blocks the penetration of water, and improves the impermeability.
6. Improve wear resistance and durability
Adding redispersible latex powder can increase the compactness between cement mortar particles and polymer film. The enhancement of the cohesive force correspondingly improves the ability of the mortar to withstand shear stress, reduces the wear rate, improves the wear resistance, and prolongs the service life of the mortar.