A novel process for simultaneous milling and coating of particulates

Ascorbic acid particulates are simultaneously milled and coated with wax in this study using a novel process based on fluid energy milling. A premix of ascorbic acid particulates and wax powders are fed into a fluid energy mill (FEM), inside which ascorbic acid particulates frequently collide with each other, wax powder particles and the wall. Consequently, ascorbic acid particulates are broken down to smaller sizes and coated with wax simultaneously. This novel simultaneous milling and coating process has several advantages compared to traditional separate milling and coating processes such as elimination of solvent usage, reduction of agglomeration, and vastly improved production efficiency. In this study the influences of the grinding air pressure and wax content on the process are investigated. The results suggest that milling and coating should be optimized collectively for this process. In general, higher energy input leads to smaller particulate size and makes it more difficult to coat, whereas higher wax content leads to higher coating coverage and larger particulate size. The wax coating slows the dissolution rate of ascorbic acid in water, especially when the wax content passes a certain threshold value.