Thermal analysis of the droplet solidification in the PGSS-process

In this work, a manufacturing process for powders from polybutylenterephthalate (PBT) is analysed in terms of the formation of differently shaped particles. For the micronization of the polymer the particles from gas saturated solutions (PGSS) process is used. Several applications require specific particle shapes and particle size distributions. In particular, spherical particles are required to obtain a free flowing powder. To optimise the quality, powders were produced at different spray temperatures and pressures and with varying mass flows of polymer and gas. With different spray conditions, powders with various shapes, morphologies and apparent densities were obtained. The temperatures before and after the expansion appear to have the main influence on the sphericity. To obtain further knowledge about the solidification process, the temperature distribution in the spray was analysed. For this purpose, heat images of the spray were taken. Based on the results, a simple model is introduced, which is able to estimate the temperature field in a polymer droplet during the spray process. An explanation for the formation of differently shaped particles is proposed.