The hidden impact of wet and dry milling processes on pharmaceutical surfaces

This study highlights how the choice of milling method can significantly influence the final properties of powdered materials. Using inverse gas chromatography (IGC), we gained deeper insights into how surface characteristics evolve with milling time across different processing techniques. The findings reveal that powders produced via dry and wet milling exhibit distinctly different surface properties. Notably, both milled naproxen samples showed increased surface energy compared to the unprocessed drug, with a marked increase in specific interactions indicating a rearrangement of surface functional groups as a result of milling. Dry-milled samples exhibited higher surface free energy, greater cohesiveness, and reduced wettability. In contrast, wet milling yielded finer particles with better wettability, lower surface energy, and reduced cohesion attributes that make them more favorable for further processing. Differences were also observed in the morphology index and relative morphology index. Dry-milled powders exhibited greater nanoroughness, whereas wet-milled samples displayed flatter, smoother surface. Overall, the study suggests that wet milling tends to produce powders with more desirable handling and manufacturing properties. These insights into surface properties provide a valuable framework for selecting the most suitable milling method helping to avoid potential issues related to powder behavior in downstream applications.