Adhesion force approximation at varying consolidation stresses for fine powder under humid conditions

- Presented an adhesion force approximation approach from the powder bulk stresses.
- A large increment in tensile strength and interparticle adhesion force above 60% RH.
- Magnitude of adhesion force depends on the RH and consolidation conditions.
- Effective interparticle contact area and capillary force variation implicated.
- Rumpf model can be extended to cover liquid bridge and load induced adhesion forces.

Interparticle adhesion forces in fine powders are greatly influenced by varying relative humidity (RH) conditions. The present study estimated the interparticle adhesion forces developed in corn starch powder under humid conditions at varying applied consolidation stresses using tensile strength determination approach. Shear test was used to determine tensile strength of powder at 1-9 kPa consolidation pressures and extrapolated values of tensile strength at zero stress were used for force estimation in non-consolidated powders. A strong dependence of interparticle adhesion force on consolidation and RH conditions was observed, mainly due to alteration in the number of adhesive contacts and contact area. The results indicated that, at low consolidation and high RH, capillary force is the prevailing force contributing to the total interparticle adhesion in contrast to higher consolidation conditions where load induced contact force plays a dominant role. Furthermore, for nonconsolidated samples, the adhesion forces registered a steep jump above 60% RH which was primarily attributed to dominance of the liquid bridge forces. Also, forces determined from tensile strength approach and those predicted theoretically, as a summation of individual forces, yielded a similar trend. Overall, a simple and effective approach for interparticle force estimation of consolidated as well as loosely packed powders under varying humidity conditions is presented here.

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