Research On Re-dispersible Styrene-Acrylic Polymer Powders By Spray Drying

Re-dispersible polymer powders is a kind of polymeric powders which can easily re-emulsified in water to reform liquid emulsion with essentially identical properties similar to the original emulsion. It is made by means of spray- drying from the emulsion. modified by protective colloids. It can be added into many cement-based architecture materials to improve its performances, and therefore it has been widely used in many industrial fields. With the development of powdered architecture material and the more rigorously demand of people for the qualities of architecture material, the requirement of high-performance redispersible powdered emulsion became more and more .A kind of styrene-acrylate emulsion with"soft core and hard shell"structure was synthesized on the basis of"the latex particle design", and and re-dispersible polymer powders were produced by spray-drying. The effects of spray drying process that influence the properties of re-dispersible styrene-acrylate polymer powders were mainly discussed.(1) Seeded emulsion polymerization based on semi-continuous process was used to produce styrene-acrylate emulsion with"core and shell"structure. MMA and St were applied as hard monomers, BA and 2-EHA acrylate were applied as soft monomers, MAA and HPMA were applied as functional monomers. The results showed that when shell Tg was 65℃~ 75℃, the total was Tg 0℃~ 5℃, emulsion viscosity was 91.5 mPa ? s, particle size was 114nm, and solid content was 45%, the emulsion was more suitable for spray drying.(2) Styrene-acrylate emulsion was modified by protective colloid and alkali. The results showed that the polyvinyl alcohol(PVA-205) should be chosen as protective colloid, in that the degree of polymerization was 500 and the degree of hydrolysis was 88%, and the concentration of 5 wt % NaOH solution should be used. When the PVA-content was 4%～6% (mass fraction based on re-dispersible polymer powders, the same below), the pH value of spray liquid was 9, the storage time was 5 hours, and the viscosity of spray liquid was controlled in15～20s, The spray liquid was suitable for spray - drying.(3) Inorganic anti-caking agents were added into re-dispersible polymer powders in order to avoid coalescence, to improve storage stability and to reduce the cost of re-dispersible powder. The results showed that when 10～12wt% ultra-fine aluminum silicate were added into re-dispersible polymer powders, the storage stability of the powders could be significantly improved.(4) Various parameters of spray drying tower were adjusted to optimize the drying process. The showed that inlet temperature of 120～140℃, outlet temperature of 70～80℃, atomizing disc running of 24000 r·min-1and feeds of 30～35 rpm were chosen as the optimal process condition.Re-dispersible styrene-acrylate polymer powders prepared by spray-drying showed superior redispersion, fine fluidity, high-quality storage stability, excellent alkali resistance and high performance-price ratio..