Abstract: In a process for the thermal after-treatment of paste-forming homo- or copolymers of vinyl chloride, obtained by aqueous emulsion polymerization, followed by spray-drying to produce a spray-dried powder, an improvement is provided wherein 20 to 60 percent by weight of the spray-dried powder is warmed for 1 second to 30 minutes to a treating temperature of 75.degree.-110.degree. C., and then is recombined with the non heat-treated, 80-40 percent by weight portion of the powder.

Abstract: The method for preparing synthetic powders based upon polyvinyl chloride or vinyl chloride copolymers by spray drying the polymer dispersions is improved by using single material nozzles with atomizing pressures of about 550 to 1000 bars where a bar is a C.G.S. unit of pressure equal to 750 mm of Hg.

Abstract: The method of preparing synthetic powders containing emulsifiers having good paste qualities by spray-drying polymer dispersions through a two-fluid atomizer having a spray ratio of about 1.6 to 5.0 kg. of spray air for each kg. of dispersion is improved. The polymer dipersions are prepared by emulsifying vinyl chloride monomer or a mixture of vinyl chloride monomer and unsaturated polymerizable compounds and polymerizing the monomers to produce polymers and copolymers of vinyl chloride. The improvement in paste qualities of the powders is achieved by introducing the spray dried powder into an air jet having a velocity from about 330 to 550 meters per second and having a weight ratio of gas to solids ranging from 1:10 to 5:1.