(30c) Micro Particles Filled with Liquid Using the Particles from Gas Saturated Solutions Technology

Encapsulation of products forms an effective protection against stress factors like oxidation or light. In addition encapsulation allows influencing the release of active substances. High pressure technologies offer new advanced possibilities for the production of fluid-filled micro particles. One of these high pressure technologies is a process called Particles from Gas Saturated Solutions (PGSS). 

Basically for the generation of fluid-filled particles using the PGSS process a shell material is provided in melted form. The liquid and an auxiliary material (a supercritical gas) are admixed in a mixing system, where the liquid is dispersed in the liquefied shell material. This dispersion is expanded through a nozzle into a spray tower to ambient pressure, forming fine droplets. Simultaneously, the Joule-Thomson phenomenon of the expanding gas causes the solidification of the droplets. Finally fine powders are obtained, which consist of the dispersed liquid encapsulated by the shell material. No organic solvents, emulsifying agents or other additives are necessary for the production of these micro composites. 

The production of fluid-filled particles has been demonstrated in the last years with many different systems. Dry and free flowing powders with a fluid content of up to 65 wt.-% were achieved. Composite powders with waxes, polymers and fats as shell material and phase change materials, water, honey and other substances as bound liquid were produced. The present research is thereby focused on systems which are forming highly instable emulsions. The experiments show that with rising liquid concentration more open composites are formed and the tap density of the powders is increased. In contrast a rising medium particle diameter is caused by rising product mass flow and a decrease of the amount of used gas. 

To study the influences of emulsion stability of the particle formation additional systems with higher emulsion stabilities were used. Compared to the instable systems, the generation of open composites could be shifted to higher amounts of liquid concentration. The dependencies of the tap density were comparable, but also moved to higher values of liquid concentration. 

The investigation shows that open and closed composites, see pictures below, can be manufactured by the PGSS process with stable as well as unstable emulsions without using emulsifiers.

Figure 1: SEM pictures of composite particles  

In Figure1 closed composites, agglomerates and porous particles filled with a liquid polymer are displayed. With increasing concentrations of the liquid the formation of open composite structures is favoured. A rising concentration of the liquid leads to the generation of open composites and rising tap densities. The possibility to produce closed composites is increased by using more stable emulsions.