Accurate quantification of particle adhesion is essential for predicting the flow behaviour of cohesive powders, as interparticle forces strongly influence bulk powder performance. Adhesion is known to depend on environmental conditions, particularly relative humidity (RH) and temperature. This study systematically investigates the combined effects of RH and temperature on particle adhesion using a Mechanical Surface Energy Tester. The experiments enable precise control of environmental conditions, allowing adhesion forces to be evaluated under well-defined RH–temperature combinations and expressed as Bond numbers to account for particle size, shape and density effects. Fifteen pharmaceutical powders were selected to represent a broad range of particle size, morphology, and true density. Three controlled RH–temperature conditions were applied for the measurements of corresponding adhesions. The study results show a complex, material-dependent relationship between environmental conditions and adhesion behaviour. At a low RH of 20%, adhesion generally increased, attributed to enhanced solid–solid intermolecular interactions in the absence of significant surface moisture. At an elevated RH of 80%, it found that in some cases reducing effective adhesion through lubrication effects and promoting improved flowability because of the formation of adsorbed moisture layers altered interfacial mechanics. Temperature further modulated adhesion by influencing material viscoelasticity and surface energy characteristics, leading to measurable changes of adhesions. These findings highlight the coupled influence of environmental conditions and intrinsic particle properties on adhesion behaviour. The outcomes provide valuable insights for predicting powder flow performance and for developing environmental control strategies in pharmaceutical manufacturing and other powder-handling applications. • Particle adhesion is detected using a mechanical surface energy tester. • The adhesion measurement is used for the calculation of Bond number. • The environmental influences on adhesion measurements are investigated. • It shows the environmental temperature increases particle adhesion and cohesiveness. • High environmental humidity will reduce the particle adhesion. • Predictions of powder flowability using Bo are confirmed by experimental results.
Garg et al. (Sun,) studied this question.