title: The influence of water on electrostatic charge retention and dissipation in pharmaceutical compacts for powder coating.
abstract: OBJECTIVE
  The electrostatic properties of five materials commonly used in tabletting were investigated to assess their suitability for the novel technique of powder coating of pharmaceutical compacts.
  
  
  METHODS
  Powder resistivity and compact voltage decay properties were determined under dry and wet conditions using purpose built equipment.
  
  
  RESULTS
  The organic materials acted as insulators having resistivities > 10(13) omega m whilst dibasic calcium phosphate showed dielectric behaviour. A clear relationship between water content and resistivity was established for all materials. Electrical conduction across powder surfaces was demonstrated as the predominant mechanism by using low concentrations of magnesium stearate. In materials absorbing significant water a bulk mechanism was also present. After charge injection, decay rates were dependent on resistivity with those having the highest values exhibiting the slowest decay. The chemical nature of the materials was unimportant except at extremely high resistivities. Conditioning of the compacts with water reduced resistivities so that decay half-lives < 1 s were achieved.
  
  
  CONCLUSIONS
  The electrical properties of the compact materials have been modified sufficiently to enable them to be considered suitable for powder coating.
authors.affiliation: Department of Pharmacy & Pharmacology, University of Bath, UK.
authors.forename: M P
authors.initials: MP
authors.lastname: Grosvenor
authors.forename: J N
authors.initials: JN
authors.lastname: Staniforth
mesh_terms: D055598:Chemical Phenomena; D002626:Chemistry, Pharmaceutical / Q000379:methods*; D002627:Chemistry, Physical; D011208:Powders / Q000737:chemistry; D012680:Sensitivity and Specificity; D055672:Static Electricity; D013608:Tablets, Enteric-Coated / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D011208:Powders; D013608:Tablets, Enteric-Coated; D014867:Water