Modification of inorganic cementitious materials such as cement with polymer emulsion has been widely used. Since the water in the emulsion will immediately react with the cement after mixing the two and finally solidify, a two-component form is used in most cases. , measure and mix each component in proportion at the construction site. This brings inconvenience to the storage, transportation and construction of materials. The emergence of re-dispersible emulsion powder has changed the above phenomenon. Redispersible latex powder is a micron-sized thermoplastic resin powder obtained by spray-drying a polymer emulsion to remove water. It can be reduced to an emulsion after adding water.Due to this characteristic, it is widely used in single-component JS waterproof coatings, polystyrene board bonding mortars for building insulation, flexible surface protection mortars, polystyrene particle insulation coatings, ceramic tile adhesives, self-leveling mortars, dry-mix mortars, etc. It is widely used in fields that require modification of inorganic cementitious materials.
RDP is a polymer powder produced by spray drying of polymer emulsion. Polymer emulsions are mostly oil-in-water systems in which thermoplastic polymers with a solid content of about 50% are evenly distributed in water with fine particles (0.1-10 μm). After losing water, the polymer particles first form dense spheres and accumulate on the surface. Under the action of energy, discrete polymer particles form a continuous polymer body. To produce redispersible latex powder by the spray drying method, a layer of PVA protective film is added to the surface of the polymer in advance. Due to the existence of the protective film, the dry powders cannot merge. In order to prevent the rubber powder from agglomerating, some fine mineral powders are also added. , such as clay, etc. However, when redispersible latex powder is mixed with alkaline substances such as cement and water, the PVA will be saponified and adsorbed by the quartz in the sand and removed. The rubber powder that has lost its protective film can eventually form a continuous water-insoluble polymer. membrane.
The particle size of the rubber powder (5-250 μm) is much larger than the particle size of the polymer dispersed phase in the emulsion (0.1-10 μm), indicating that the latex particles will agglomerate during the spray drying process. In order to reduce the tendency of polymer powder to agglomerate during long-term storage, inert fluid materials such as clay, talc, silica and other fine particles are usually added to the dry powder as anti-stick fillers. The filler is determined according to the type of polymer and its glass transition temperature. The dosage is generally 8%-30% of the dry polymer powder, which is the main source of ash in redispersible latex powder. After redispersible latex powder is redispersed, the diameter of the latex particles becomes about (0.1-10μm).
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