title: Powder flow in an automated uniaxial tester and an annular shear cell: a study of pharmaceutical excipients and analytical data comparison.
abstract: BACKGROUND
  An automated version of uniaxial powder flow testing has recently been developed and there is a need for experimental data from pharmaceutical powders.
  
  
  OBJECTIVE
  To compare the novel testing method with an annular shear cell using different pharmaceutical excipients. A particular aim was to gain an improved understanding of potential differences in the obtained flow results.
  
  
  METHODS
  Nine excipients were studied with both flow testers at different consolidation levels. Unconfined yield strengths were determined at similar major consolidation stresses. Finally, an anisotropic stress factor was calculated and the fractal character of the powders was assessed by means of image analysis in a rotating drum.
  
  
  RESULTS
  Data correlated generally well; however, the unconfined yield strength from uniaxial testing resulted mostly in lower values compared to annular shear cell testing. Differences were specific for the given excipients and mannitol demonstrated the highest discrepancy of measured flow parameters. The differences were first discussed by considering wall friction, anisotropy of forces, brittleness as well as the fractal nature of the powder surface. This heterogeneity of the powder as well as the anisotropy of forces was also found to be important for the relative flow index.
  
  
  CONCLUSIONS
  The automated uniaxial method demonstrated faster and more reproducible flow testing as compared to an annular shear cell. Therefore, the new method has a high potential in pharmaceutics for example in the quality-control of powders.
authors.affiliation: University of Applied Sciences and Arts Northwestern Switzerland, Institute of Pharma Technology, Gründenstr.40, CH-4132, Muttenz, Switzerland. martin.kuentz@fhnw.ch
authors.forename: Martin
authors.initials: M
authors.lastname: Kuentz
authors.forename: Peter
authors.initials: P
authors.lastname: Schirg
mesh_terms: D016880:Anisotropy; D002482:Cellulose / Q000737:chemistry*; D055598:Chemical Phenomena; D004339:Drug Compounding / Q000295:instrumentation*; D005079:Excipients / Q000737:chemistry*; D065347:Hypromellose Derivatives; D007785:Lactose / Q000737:chemistry*; D008353:Mannitol / Q000737:chemistry*; D008422:Materials Testing; D055595:Mechanical Phenomena; D008747:Methylcellulose / Q000031:analogs & derivatives / Q000737:chemistry; D010316:Particle Size; D011205:Povidone / Q000737:chemistry*; D011208:Powders; D025341:Principal Component Analysis; D011786:Quality Control; D012212:Rheology; D013213:Starch / Q000737:chemistry*; D013499:Surface Properties; D013557:Switzerland
chemical_list: D005079:Excipients; D011208:Powders; D065347:Hypromellose Derivatives; D008353:Mannitol; D002482:Cellulose; D008747:Methylcellulose; D013213:Starch; D011205:Povidone; D007785:Lactose; C109691:microcrystalline cellulose