Crystallization & Encapsulation in multicomponent mixtures (COMPLETED)

In this project, the crystallization and microencapsulation in multicomponent mixtures are studied.

Introduction

Microencapsulationof powders is applied in many fields of research, for example in food, pharmaceutical and consumer products. It is a process in which particles or droplets are surrounded by a layer of coating material. Using encapsulation, the surface of particles can be tailored to specific properties, like compatibility or reactivity with other materials, protection from degradation, controlled release of core material and improved shelf life. When the materials are sensitive, e.g. reactive/explosive or unstable at higher temperature, the encapsulation technique must operate under conditions that are mild enough for the core material to survive. In this project a number of microencapsulation techniques is used to desensitize, protect or improve compatibility of the sensitive core particles, or to enable the study of fundamental properties and processes.

Multicomponent systems

For the creation and the microencapsulation of particles, the control of solid phase formation in multicomponent systems is required. In case of organic, crystalline materials, this considers the (heterogeneous) nucleation and growth of the crystalline phase. Information of primary importance is the solubility of the compound(s) in the solvent. A novel method to determine the solubility, based on a scarcely used principle, is developed and validated. In this method the solubility is determined by the addition of solvent to a suspension of known composition at constant temperature. This method is particularly useful in multicomponent mixtures, where for example the solvent composition can be altered. While controlling the interactions between crystalline compound and solvent in terms of solvate formation by using co-solvents, this method proved a valuable tool to track the solubility of the compounds along the entire range of solvent compositions. 

Electrospray crystallization

For the encapsulation of crystalline organic substances with other crystalline organic substances, the core particle and coating can be produced in a single processing step. Concomitant electrospray crystallization is a process that uses a high electric field to produce micron sized droplets of solutions containing multiple solutes. Using this technique it is possible to combine two materials in a single particle, where they would not do so in concomitant cooling crystallization. In the case of explosives RDX and TNT, this reduced the impact sensitivity of the combined particles to be not greater than the least sensitive material, where it would be expected that the sensitivity would at least be a weighted average of the two materials.

 

Immobilization

In a novel process for the production of meat analogs, a couette cell is used to create a fibrous structure out of a mixture of nutrients and water. The main fiber-forming component in these mixtures is gluten. However, gluten instantly forms fibers in contact with water, which leads to material losses due to stickiness during the preparation steps. Therefore, the gluten need to be protected from water before the start of the process. Immobilization of gluten in a food grade polymer (κ-carrageenan, hydrogel), using a dripping technique with a vibrating nozzle (Buchi Encapsulator) and a cooling or crosslinking bath, prevents the fibers from forming until, by shear and temperature supplied by the meat analog production process, the gluten are released. The same technique is applied for immobilization of aluminium in a polyethyleneglycol (PEG) matrix to prevent oxidation of this fuel due to exposure to air. Here, a suspension of aluminum particles in molten PEG is run through a single nozzle and the droplets are solidified in a cooling bath.

Nucleation in hydrogels

Using a concentric nozzle in the Buchi Encapsulator oils and solutions are encapsulated to study the nucleation events inside a hydrogel. Thymol and Nerolin Bromelia are molten and subsequently encapsulated in calcium alginate, after which induction time measurements are performed. The nucleation of solutions is also investigated in calcium alginate encapsulated particles. The induction time of various degrees of supersaturation of fenofibrate in heptane is studied.

Atomic Layer Deposition

In pyrotechnic compositions, materials are combined to generate the desired effect. However, sometimes these materials are incompatible with each other, meaning that they react (violently) without an ignition source. Ammonium nitrate and perchlorate salts are an example of such a combination. In order to use these materials in a single composition, where the reaction may only occur after ignition, a thin impervious layer should protect the ammonium nitrate from the perchlorate salt until ignition. Ammonium chloride is used as model compound for ammonium nitrate, and is coated with a small number (<20) of monolayers of e.g. Al2O3. Atomic Layer Deposition is used for this application, where the core particles are suspended in a fluidized bed, and the coating layer is applied by having two precursors react with the particles in series. Using the same technique, aluminum particles are coated with a fluoride containing coating for activation purposes.