The Preparation Of Redispersible Polymer Powder With Core-shell Structure And Its Application Performance

Redispersible polymer powder is a kind of powder which can be disperse in the water to reconstruct a stable and uniform emulsion with the same properties as the original emulsion. Redispersible polymer powders are usually prepared by spray drying, the original emulsions which are synthesized by emulsion polymerization. As a kind of additive for building materials, redispersible polymer powder could be used with cement to improve the flexibility and waterproofness of concrete or cement mortar. It also could be used in powder coating, powder adhesives, etc. One of the main advantages offered by redispersible powders over the ordinary liquid emulsions is their ability to be dry-mixed with hydraulic binders, aggregates, and other ingredients for the manufacturing of monocomponent formulations ready to use at the job sites. In addition, as a new and promising application field, redispersible polymer powders also could be used as solid binders for dry-powder coating.In the paper, the styrene-acrylate polymer emulsions with a latex pratical structure of soft core and hard shell were synthesized by emulsion polymerization with styrene-butyl acrylate-methyl methacrylate as co-monomers, and the redispersible polymer powders were prepared by spray drying of the prepared emulsions. The effects of structure of the latex particles, latex glass transition temperature, core-shell ratio of monomers, the content of initiator, styrene (St) hydroxypropyl methacrylate (HPMA), N-(hydroxymethyl) acrylamide (NMA) on latex properities, emulsion film performance as well as dispersible polymer powder properties were investigated. Fourier transform infrared spectrometer(FTIR), differential scanning calorimetry (DSC), nano-laser particle analyzer, high-speed centrifuge, transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric analysis (TG) and other laboratory equipments were used in the experiments to characterize the properties of the prepared emulsions and redispersible polymer powders.The results showed that the sybthesuzed emulsion with the structure of soft core and hard shell was appropriate for spays drying, and then the redispersible polymer powder with good performance could be obtianed. Under the conditions of the ratio of the core to shell was 2:1, the content of initiator was 0.5%, the content of St was 20% of shell- polymerization monomers, HPMA was 2%, and NMA was 2.5% of shell- polymerization monomers, the desined emulsion and redispersible polymer powders with good properties could be obtained.By mixing the styrene-acrylate redispersible polymer powders with inorganic pigments, cellulose ether, powder defoamers and dispersant agents, a new kind of dry-powder coating was prepared. The effects of redispersible polymer powder, cellulose ether and powder defoamers on the film-forming ability, workability, water-resistance and abrasive resistance of dry-powder coatings were tested and discussed. The experimental results showed that when the content of redispersible polymer powder was 30%, the dry-powder paints had excellent properties which could meet the technical requirements of national standard GB/T 9756-2009 for interior wall emulsion coatings, and no other volatile organic compounds (VOC) and toxic materials could be found. Therefore, the dry-powder coatings based on the redispersible polymer powders prepared in this experiment had the same properties as the traditional liquide emulsion paints,s and had broad and promising application prospects.