A processing route to spherical polymer particles via controlled droplet retraction

In this work we describe the production of spherical polymer particles from thermoplastic polymers. A simple method is developed to transform rough powders into spherical particles. The polymer particles are molten in heated oil whereafter interfacial tension driven reduction of curvature and shape retraction induce a transformation to the equilibrium spherical shape. The sphericity of the particles is validated by determining the aspect ratio, roundness, as well as circularity. Furthermore, batches of narrow particle size distribution are attained by sieving on different mesh sizes. The effects of the material characteristics and processing conditions are investigated and rationalized based on the governing physical processes and their scaling relations. As a result, the processing conditions can a priori be tailored depending on the material characteristics. The versatility of the method is confirmed by generating spherical particles from various thermoplastic polymers including PS, LDPE, PP, PA12 and PA12 filled with carbon nanotubes.