Powder bulk behaviour is a major concern in powder processing and manufacturing industries that could affect various processing operations like tablet compression, mixing, handling leading to poor product quality and performance. Powder cohesion or adhesion is influenced by the intrinsic material properties (surface chemistry, mechanical properties), particle attributes (particle size, shape, surface roughness), extrinsic factors such as processing (milling, mixing) and environmental conditions like humidity (RH). Additionally, the role of surfaces or interfacial properties of particulate solids cannot be undermined in governing all the interparticle interactions affecting the powder behaviour. In our work, we have investigated the RH induced bulk cohesion of mannitol powder using a surface energy-based cohesion force model. Furthermore, the formulation and characterisation of powder mixtures is critical to obtain quality pharmaceutical product. Here, we also report the effects of interparticle structuring in binary powder system on its surface property like surface energy is examined using Inverse Gas Chromatography (IGC) technique. We show that the structuring of component particles in binary compositions affects the solid-solid interfacial properties. Three different scenarios viz. structured, random and segregated systems of the binary powder composition were considered for the analysis in the IGC column. Binary mixtures with large size disparity between the components produced structured mixtures exhibiting a guest-host type of interactions and energetic homogeneity irrespective of the energetics of the finer component. Furthermore, an approach to decouple the effect of the contribution of milling induced increase in surface area and surface energy was presented by tailoring the surface chemistry through surface silanisation of the crystal surfaces. Surface silanisation resulted in normalisation of the surface energy heterogeneity for unmilled and milled powders. Thus, our work highlights the importance of surface interactions in single and binary component powder systems by emphasising on the phenomenon of particle structuring among the component particles.

Mixture design and surface properties: Role of interparticle structuring in binary powder systems

ACS Fall 2021

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