Study On Preparation And Performance Of Redispersible Polymer Powders

Redispersible polymer powders were a kind of powders which could disperse in the water to be a stable and uniform emulsion meanwhile could keep the same properties as the original latex. They were usually synthesized by emulsion polymerization, and then prepared by spray drying with some assistant agent mixed. Redispersible polymer powders were used as a kind of additive for building materials. They could be used with cement to improve the flexibility and waterproofness of concrete or cement mortar. They also could be used as powder coating, powder adhesive, etc.In the paper, vinyl acetate- butyl acrylate (VAc-BA) copolymer system and butyl acrylate-methyl methacrylate (BA-MMA) copolymer system were used for emulsion polymerization and preparing redispersible polymer powders.The Fourier transform infrared spectrometer(FT-IR), differential scanning calorimetry (DSC), nano-laser particle analyzer, instrument for viscosity, high-speed centrifuge, transmission electron microscope (TEM), scanning electron microscope (SEM)and other laboratory equipments were used in the experiments to characterize certain properties.To the VAc-BA system, The influence of the amount of acrylic monomer(AA), emulsifiers (DSB), protective colloid (PVA), and stabilizer (NaHCO₃) on the emulsion's performance were discussed. As the result showed, the optimum amounts of AA, DSB, PVA and NaHCO₃ were 2.5wt%, 0.2wt%, 4-6wt%, 0.3wt% separately basing the mass of monomers. And in this case, the latex present better stability and film-redispersibility. Because the film of Poly(VAc-BA) system was easy to form, it was difficult to collect enough polymer powders by spray drying. At last, the situation was improved by increasing the amount of anti-caking agent, adding more protective colloid and changing the proportion between VAc and BA.To BA-MMA system, the influence of content of emulsifier (DSB), the proportion between core and shell monomers and content of MAA in shell monomers on properties of latex were studied. It was found that, when the content of DSB over 0.5wt% of monomer, the latex was more stable; The soft core- hard shell structured latex particles by controlling the proportion between core and shell monomers; when the content of shell monomer was not more than 30wt% of total monomers and the mass proportion of BA to MMA to MAA in the shell monomers was 2:7:1, the minimum film forming temperature was lower than 30℃. And the redispersible polymer powders with average size in 1-40μm and good redispersiblility were prepared by the above structured copolymer system of BA-MMA-MAA. With the increase of the content of shell monomers, the film forming ability of the polymer powders worsen. So the proper content of shell monomers was lower than 30%.While the redispersiblity of the polymer powders was improved with the increase of the content of MAA.