Flowability

The ease at which powder flows is a practical challenge in pharmaceutical processing. Flow can have a significant impact on manufacturing efficiency. It has an impact on the speed at which a tableting machine can run, and it has an impact on the final product dose uniformity. 

Flowability is the result of material physical properties and the equipment used for handling, storing, or processing material. Flow behavior (and ranking) of powders may be different between applications, as it depends on the stress state and flow field. Flowability can be improved by adjustment of physical properties or by changing the flow field or stress state.

Illustration of different types of flow issues.

 

Flowability can be improved by adjustment of the physical properties of the formulation

  • Reduce cohesiveness, internal friction (1,5)
  • Reduce wall friction (2,5)
  • Reduce electrostatics by using low charging excipients (3)
  • Increase density (4)
  • Increase permeability (4)
  • Increase homogeneity of the formulation (5)
  • Increase ratio DC lactose: MCC
  • Add flow aids/glidants
  • Optimise PSD: coarse particles are generally less cohesive
  • If dissolution allows, coarsen API
  • Optimise shape and surface: spherical particles 
    (spray dried/granulated lactose) tend to have better flow properties

 

Flowability can be improved by adjustment of the flow field or stress state

  • Increase hopper/feeder aperture (1, 4, 5)
  • Increase time for the formulation to flow into the dies by slowing down the tablet press (4,5)
  • Reduce hopper wall angle (2, 5)
  • Reduce electrostatics by reducing frictional contacts, grounding of the feeder, coating or electro-polishing equipment (3)
  • Reduce hopper fill height
  • Aerate powders by mechanical assistance (paddle feeders, blades, agitators)
  • Optimise humidity to reduce electrostatics and capillary interactions

(*) numbers indicate preferred way forward for specific issues