Study On Preparation Of Re-dispersible Styrene-acrylic Polymer Powders

Re-dispersible emulsion powder is a kind of polymer powders made from special emulsion by means of spray- drying. It can be easily re-dispersed in water and reform liquid emulsion with essentially identical properties to the original emulsion. Styrene-acrylate polymer emulsion are widely used in coatings and adhesives, because of its excellent application properties, such as acid-alkali resistance and corrosion resistance. Therefore, it's of great significance to prepare re-dispersible styrene-acrylate emulsion powders.In this research, the core-shell structure styrene-acrylate polymer emulsion was synthesized on the basis of"the latex particle design", and re-dispersible emulsion powders were produced by spray-drying.Seeded emulsion polymerization based on semi-continuous process was used to produce a kind of styrene-acrylate emulsion with"soft core and hard shell"structure, low viscosity and good performance. The effects of some factors, including of emulsifier, initiator, mass ratio of core to shell and functional monomer (MAA, NMA), on properties of styrene-acrylate emulsion were mainly discussed. The results showed that when the content of emulsifier, initiator was 1% (mass fraction based on the whole monomer, the same after) and 0.6% respectively, and the mass ratio of core to shell was 2/1, the stale styrene-acrylate emulsion was prepared with a narrow size distribution. The solid content was 45.2%, the viscosity was 91.5 mPa.s, the average size was 122 nm. It had been confirmed that the emulsion had an obvious core-shell structure through a series of analysis, such as Differential scanning calorimetry (DSC), Transmission election microscopy (TEM). The emulsion with good performance was suitable for spray - drying.NaOH was used to adjust the emulsion pH value, and protective colloid (PVA) was put into emulsion to improve its drying properties before spray - drying. The re-dispersible emulsion powders were obtained by spray-drying. The influence of the pH value, the content of protective colloid and the inlet temperature on re-dispersible powders properties were studied. The results showed that when the pH value was about 9, the content of PVA was between 6% and 8%( mass fraction based on re-dispersible emulsion powders, the same after), the inlet temperature was between 120℃and 140℃, the styrene-acrylate re-dispersible powders could be prepared with good redispersibility and good flowability. For the final products, the water content was 2.3-2.7%, the average size was 38-39μm. It was confirmed that the re-dispersible powders could be easily re-emulfied into liquid emulsion with good film-forming properties by scanning electron microscopy (SEM).Re-dispersible emulsion powders were widely used in powdered architecture materials, but it was seldom used to prepare zero VOC powder coatings. In this paper,zero VOC powder coatings based on the prepared re-dispersible emulsion powers were made successfully, to reduce the VOC content in common architecture coatings, which was very meaningful both in academic and in practice.