Sabine Kareth

Particle Formation from Gas-Enriched Polymeric Melts and Polymeric Solutions

Within the scope of this subproject, a gas-assisted high-pressure spray process (PGSS—Particles from Gas-Saturated Solutions) was investigated. The gas used for the atomization is carbon dioxide (CO2) which for the most purposes is in supercritical state. In the spray process, the gas is partly dissolved into the liquid before the atomization. The dissolved CO2 changes the physical properties of the liquid such as viscosity and surface tension and enables high-viscous substances to be atomized. Several authors were able to atomize high-viscous substances such as polymers, fats, and waxes with such a spray process. Nevertheless, till now the fundamental influence of the CO2 on the atomization phenomena has not been taken into account. For this reason, experiments which shall clarify how the CO2 affects the spray and particle formation have been carried out systematically within this project. Sprays of water, polymers, and aqueous polymeric solutions were observed and investigated. The liquids were sprayed as pure substances as well as CO2-enriched substances from an autoclave in a batch wise working process. To get a deeper understanding of the observed effects, optically transparent spray geometries were developed. Observations of the flow regime of the gas-enriched liquids gave explanations of the governing atomization phenomena. The results of the experiments show that the working principle of the PGSS process is based on the phenomena of flash atomization. Classical phenomena such as jet and lamella breakup can be neglected for the continuously working process. In further experiments, powders of polyethyleneglycols (PEG 6000) were generated using the continuously working process. Several spray devices were used such as hollow cone nozzles, capillaries, and orifices. The results show that powders with average particle size distributions in the order of 100 μm can be generated independently from the design of the spray device. Therefore, it is proven, that the flash atomization is the governing working principle in the PGSS process.