In-line implementation of an image-based particle size measurement tool to monitor hot-melt extruded pellets

Daniel Treffer, Patrick R. Wahl, Theresa R. Hörmann, Daniel Markl, Simone Schrank, Ian Jones, Paul Cruise, Reinhardt-Karsten Mürb, Gerold Koscher, Eva Roblegg, Johannes G. Khinast

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


This work focuses on the implementation and application of an in-line particle measurement tool to monitor particle properties of hot-melt extruded pellets. A novel image analysis system (Eyecon) is used to analyze pellets with a size of approximately 1 mm. The method is based on photometric stereo imaging, which is achieved by three different-colored light sources arranged circularly around the lens. Several implementations, whereby the product stream was led through the optical sampling volume, have been tested. The advantages and disadvantages of each implementation are discussed and evaluated. The most suitable implementation was applied to an extrusion run with constant throughput and different cutting frequencies resulting in different pellet sizes. A particle size distribution comparison between the image analysis system and an off-line reference particle analysis (QICPIC) showed good agreement although only a small fraction of the particles were analyzed in-line. Additionally, some illustrative examples for process development are given. With this approach the capability of hot-die face pelletizing to manufacture nearly-spherical pellets with a narrow size distribution is proven.

Original languageEnglish
Pages (from-to)181-189
Number of pages9
JournalInternational Journal of Pharmaceutics
Issue number1-2
Early online date11 Mar 2014
Publication statusPublished - 15 May 2014


  • hot-die face pelletizing
  • hot-melt extrusion
  • measurement position
  • particle imaging
  • process analytical technology

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