On the properties and application of beeswax, carnauba wax and palm fat mixtures for hot melt coating in fluidized beds

Abstract

Coating of particulate solids is a well-known process within the chemical, pharmaceutical and food industry. Most of these industries use it to achieve a defined product behavior. Melt-coatings, in this paper beeswax, carnauba wax and palm fat, are more difficult to apply compared to solvent-based coatings because of the complex solidification behavior.This contribution focuses on the experimental investigation of the crystallization process. The thermal crystallization behavior of mixtures of beeswax, carnauba wax and palm fat is investigated to determine the processability and the achievable coating quality prior to lab trials. Mixing of the melts results in a broadening of the crystallization temperature range, making the process more challenging. The rheological behavior in the phase transition of different mixtures shows a rather sudden change in the flowability contrary to the extended thermal solidification. The sudden change is a consequence of the linking of the appearing crystals, which was visualized at different solidification temperatures by polarization microscopy. The Martens hardness of the solidified material was adjusted by blending between 2 and 17 N/mm2. The coating was applied in a lab-scale fluidized bed based on parameters determined from the characteristics. A micro-computed tomography image shows a closed coating of varying thickness. It was possible to predict the coating process with these natural products out of the material properties, and adapt them by blending. Furthermore the results of this contribution show that there is a gap between the pure processabilty and the achievable coating quality.