Tailor-made composites by high pressure spray processes

The generation of powderous composites by the PGSS (Particles from Gas Saturated Solutions) process is topic of this investigation. The PGSS process, a high pressure spray process, is suitable for the micronisation of several substances and various polymers. With a couple of previous investigations it was shown, that fine powders with different morphologies can be manufactured [1-6]. Aim of this investigation was the generation of multi-phase composites by the use of the PGSS process. For this purpose, a substance to be encapsulated (core material) is mixed with a second component (shell material), which is intended to form a firm shell, in a static mixer at high pressure. A non stabilized emulsion is formed and supercritical carbon dioxide is admixed. Subsequently, the mixture is expanded through a nozzle in a spray tower. Fine droplets are formed and are rapidly cooled down below the solidifying temperature of the shell material, due to the Joule-Thomson effect of the expanded carbon dioxide. Thus fine powder is formed and can be easily separated from the gas e.g. by the help of a cyclone. Different material combinations were chosen in order to demonstrate property dependencies of the generated composites from the process parameters, the used material combinations and the emulsions stability. The investigation shows that open and closed composites can be manufactured by the PGSS spray process with stable and unstable emulsions. The probability to produce closed composites increases by using more stable emulsions. An increasing amount of the component to be encapsulated leads to the generation of increasingly more open composites. The experiments show also that with rising concentration of the bound component the bulk density is increased.