Positive vs. negative electrostatic coating using food powders

Previous studies on electrostatic coating of food powders using negative corona have showed benefits such as an increase in coating deposition and a more even coating. However, no work has been done on the advantages of positive corona. Thus, this study was aimed to determine whether positive or negative corona produced better coating for different food powders. Twenty-three powders were coated onto five aluminum strips using an electrostatic powder applicator. Transfer efficiency (TE), adhesion and dustiness were measured and correlated to particle size, flowability and tribocharging value. The polarity of the tribocharging value for each powder determined whether positive or negative corona produced higher TE. For most proteins, positive corona produced higher TE than negative corona since proteins tribocharge positive. Most carbohydrates tribocharge negative; thus negative corona produced higher TE than positive corona. Salts had relatively small tribocharge values; thus there was no difference between TE of positive and negative corona. No significant difference was observed between positive and negative corona for adhesion and dustiness, though electrostatic coating produced higher TE and adhesion and less dust than nonelectrostatic coating.