EFFECTS OF PARTICLE SIZE AND DENSITY ON SEPARATION OF MIXTURES DURING NONELECTROSTATIC AND ELECTROSTATIC POWDER COATING A Thesis Presented in Partial Fulfillment of the Requirements for The Degree Master of Science in the Graduate School of The Ohio State University By Chanun Somboonvechakarn, B.S. ***** The Ohio State University 2009 Master’s Examination Committee: Dr. Sheryl A. Barringer, Advisor Approved by Dr. V.M. Balasubramaniam _____________________________ Dr. John Litchfield Advisor Graduate Program in Food Science and Technology Copyright by Chanun Somboonvechakarn 2009 ABSTRACT Powders used during coating usually consist of a mixture with different physical properties, such as particle size and density. Two mixtures with the same composition but different sizes: 44 and 256 µm NaCl, and 64 and 191 µm starch; and two mixtures with sizes close to one another but different densities: 44 µm NaCl and 64 µm starch, and 197 µm NaCl and 191 µm starch, were nonelectrostatically and electrostatically coated on grounded targets. Separation of mixtures was measured by comparing the percentages of each powder on the target to determine whether size caused separation. Targeting loss and adhesion loss, when coated individually and in mixtures, were determined. During nonelectrostatic coating, mixtures of NaCl and starch separated by size due to the difference in targeting losses between small and large powders, both individually and in mixtures. Adhesion losses had a small effect. Interactions occurred due to being in a mixture reduced separation for NaCl, but increased separation in starch. Separation occurred because there was more large powder on most or all locations. During electrostatic coating, separation by size occurred due mainly to differences in adhesion loss in mixtures. For both NaCl and starch mixtures, there were more small powders closer to the nozzle due to electrostatic charge, while more large powders landed further away from the nozzle, causing separation, however, electrostatics did not affect separation compared to nonelectrostatic coating. ii Differences in density caused separation during nonelectrostatic coating of small mixtures. The separation was due mainly to differences between individual targeting losses, while the difference in adhesion losses was a less significant factor. There was more starch than NaCl on all targets, due to the differences in targeting losses. The interactions due to mixture increased separation. No separation was observed in the mixtures of large particles with different densities. During electrostatic coating, the differences in the individual targeting losses were large, but became insignificant when in the mixture. The differences in the individual adhesion losses were also large, but became smaller when in a mixture. In the small mixtures, there were more starch particles closer to the nozzle during electrostatic coating. Overall, nonelectrostatic coating causes high targeting loss for all powders, therefore coating systems need to be designed to minimize the problem. Electrostatics coating increased the differences in adhesion loss, therefore methods such as adding oil to the surface of the targets need to be applied in order to reduce adhesion loss difference. iii ACKNOWLEDGEMENTS I wish to thank my advisor, Dr. Sheryl A. Barringer, for her guidance and encouragement, which made this thesis possible, and for her patience in correcting my errors. It has truly been a privilege for me to be under her guidance and supervision for the past two years. I thank Yichi Xu and Yang Huang, my fellow colleagues, for discussing with me various aspects of this thesis, and for helping me with various equipment problems. I am grateful to Inggrayani Herlambang for helping me to handle various statistical problems I encountered during the data analysis, and her moral support. I also wish to thank my parents, Sittichai and Ladda Somboonvechakarn, for their encouragement and moral support throughout my graduate school years. iv VITA January 9, 1984…………………………………………….. Born- Bangkok, Thailand 2007…………………………………... B.S. Food Science, The Ohio State University 2007-present…………………………………………… Graduate Research Associate, The Ohio State University FIELDS OF STUDY Major Field: Food Science and Technology v TABLE OF CONTENTS ABSTRACT..............................................................................................................ii ACKNOWLEDGEMENTS...................................................................................... iv VITA......................................................................................................................... v LIST OF TABLES .................................................................................................viii LIST OF FIGURES..................................................................................................ix Chapters: 1 LITERATURE REVIEW: SEPARATION IN MIXTURES DURING NONELECTROSTATIC AND ELECTROSTATIC POWDER COATING .............. 1 1.1 Introduction ................................................................................................... 1 1.2 Transfer efficiencies.......................................................................................3 1.2.1 Effects of particle size on transfer efficiency ............................................ 3 1.2.2 Effects of density on transfer efficiency.................................................... 5 1.2.3 Effects of resistivity on transfer efficiency................................................ 6 1.2.4 Losses contributing to decreased transfer efficiency ................................. 7 1.3 Adhesion........................................................................................................ 8 1.3.1 Effects of particle size on adhesion............................................................ 8 1.3.2 Effects of resistivity on adhesion............................................................... 9 1.4 Factors affecting separation of mixtures during nonelectrostatic and electrostatic coating ........................................................................................... 10 1.4.1 Effects of transfer efficiencies of individual components on separation .. 12 1.5 Trajectories of powders in a polydisperse system ................................. 13 1.5.1 Trajectories of powders in mixtures during nonelectrostatic coating....... 13 1.5.1.1 Particle size profile of mixtures during nonelectrostatic coating........ 13 1.5.1.2 Particle velocity profile of mixtures during nonelectrostatic coating . 15 1.5.2 Trajectories of powders in mixtures during electrostatic coating............. 16 1.5.2.1 Particle size distribution and trajectories of particles in a polydisperse system during electrostatic coating............................................................... 17 1.5.3 Particle velocity profile of mixtures during electrostatic coating............. 20 1.6 Conclusion................................................................................................... 20 2 EFFECTS OF PARTICLE SIZE ON SEPARATION OF MIXTURES DURING NONELECTROSTATIC AND ELECTROSTATIC POWDER COATING ............ 22 2.1 Abstract ....................................................................................................... 22 2.2 Introduction ................................................................................................. 23 2.3 Materials and Methods................................................................................. 25 2.3.1 Determination of separation ...................................................................... 25 2.3.2 Targeting loss and adhesion loss determination ......................................... 26 2.3.3 Determination of interactions between particles in mixtures of different sizes .......................................................................................................................... 27 2.3.4 Statistical analysis..................................................................................... 28 vi 2.4 Results and discussion.................................................................................. 28 2.4.1 Differences in particle size caused separation in NaCl and starch mixtures during both nonelectrostatic and electrostatic coating....................................... 28 2.4.2 Individual targeting losses....................................................................... 30 2.4.3 Targeting losses of powders in a mixture................................................. 32 2.4.4 Individual adhesion loss .......................................................................... 34 2.4.5 Adhesion losses in mixtures .................................................................... 36 2.4.6 Separation............................................................................................... 37 2.5 Conclusion................................................................................................... 39 2.6 References ................................................................................................... 41 2.7 Tables and Figures ....................................................................................... 44 2.7.1 Tables ..................................................................................................... 44 2.7.2 Figures.................................................................................................... 46 3 EFFECT OF PARTICLE DENSITY ON SEPARATION OF MIXTURES DURING NONELECTROSTATIC