Analyzing the interparticle batch homogeneity of natural hot-melt coatings

The hot-melt coating process is widely used in the food and pharmaceutical industries. Its purpose of use is very diverse and includes, among other things, changing the functional properties of the particle surfaces, forming a protective layer or influencing the release rate of the encapsulated substance. To achieve such purposes for each product particle, a high degree of uniformity of coating of the single particles and a high interparticle batch homogeneity are required. However, such requirements are affected by multiple factors throughout the hot-melt coating process. The main focus of this research is to evaluate the interparticle batch homogeneity, and to compare the results with alternative methods for coating quality analysis. As a testing system, sugar spheres are coated with hydrogenated palm oil in a lab-scale Wurster fluidized bed. The coatings are investigated under various process conditions using particle size measurement and micro-computed tomography analysis. Additionally, a new method based on fluorescence spectroscopy is proposed to quantify interparticle batch homogeneity unaffected by structural phenomena such as delamination. For the investigated test system, the results of this study show that a process temperature of 40 °C has the most favorable effect on the interparticle batch homogeneity, while spray rates between 3 and 20 g/min have only a minor influence.