Experimental investigation of adhesion between powders and surfaces

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Abstract
The adhesion between two pharmaceutical powders (poly (ethylene glycol) 4000 and Sta-Rx 1500) and various metal and polymer substrates has been investigated. The powders were either deposited on the substrates with negligible force or forced on by spinning in a centrifuge. The force required to remove the particles was then evaluated by spinning the substrate-powder samples in a centrifuge and counting the remaining powder after rotation at various spéeds. The median adhesive force between the powders and various substrates was similar in the case of particles deposited with negligible force, with the exception of adhesion to PTFE, which was about one-third of the force. After the powders had been forced on to the substrate surface the median adhesive force increased. This increase was approximately five-fold for the Sta-Rx 1500 and up to thirty-fold for the PEG 4000. Differences in the adhesion between each powder and the various substrates were now evident with, for example, Sta-Rx 1500 adhering to stainless steel with a force of 1510 times 10−9 N, but to Dural with a force of 2380 times 10−9 N.