Effects of surface properties on the tribocharging characteristics of polymer powder as applied to industrial processes

Experiments performed on different powders of different size distributions tribocharged with stainless-steel (SS) beads showed the charge acquired by the powder could be correlated with the actual work function difference between the powder and SS. Ultraviolet and X-ray photoelectron spectroscopy were performed on various materials involved, and showed the work function increased with surface contamination and oxidation, and the difference narrowed for metals and polymers. Such a small difference in work function may contribute to bipolar charging. Experiment data showed that while charge acquired increased with particle size, the charge distribution was generally bipolar. Both surface analysis and charge distribution studies suggest that for tribocharging, minimization of oxidation and surface contamination are needed. It also appears that the relative humidity must also be controlled to obtain reliable tribocharging. Semiempirical molecular modeling calculations of the work function of several polymers showed good agreement with experiment. Surface plasma treatment is presented as a viable method for modifying the work function. Index Terms--Bipolar charge distribution, powder coating, tribocharging, ultraviolet photoelectron spectroscopy (UPS), work function, X-ray photoelectron spectroscopy (XPS).