Researchers control static charge using electric fields

Scientists from RMIT University and Riga Technical University have demonstrated that externally applied electric fields can change the amount and polarity of static charge remaining after two plastic surfaces make contact and separate. The laboratory research could eventually lead to new approaches to controlling unwanted electrical charging during powder processing, although food ingredients and industrial handling equipment have not yet been tested.

The findings were published in Nature Communications on 15 October and explained in institutional communications issued during the following week. The experiments demonstrated that an applied electric field could increase, reduce or reverse the charge left on selected materials. Under suitable conditions, the researchers also showed that the resulting residual charge could be suppressed.

The work examines contact electrification, the accumulation of charge associated with materials touching and separating. The effect is encountered when plastic films move across equipment, particles travel through handling systems or different surfaces rub against one another. Charge can influence how materials cling, separate and move, making it an important variable in industrial processes involving dry powders.

The research team included Andris Šutka and colleagues at Riga Technical University, Peter Sherrell at RMIT, and contributors from the University of Melbourne. Their investigation combined laboratory measurements with computational models to examine how electric fields influence charge separation. The results support the interpretation that fields generated within contacting materials contribute to the final distribution of electrical charge.

In the principal experimental arrangement, polystyrene surfaces were repeatedly pressed together and separated while an external electric field was applied. Tests included 500 contact and separation cycles, allowing the researchers to examine changes in measured surface charge under different electrical conditions. The supporting work also considered other plastics, although the experiment was not designed around food powders.

Increasing the applied field changed the magnitude of the charge remaining after separation, while reversing the field could reverse the charge polarity. The observations establish a way of influencing charging under the conditions tested, rather than relying exclusively on the choice of two materials to determine the final result.

The underlying mechanisms of contact electrification remain an area of scientific debate. Researchers have investigated the possible movement of electrons, ions and other charge carriers between surfaces. The latest study addresses the forces influencing charge separation, demonstrating that an externally controlled field can materially change the measured outcome without settling every question about the identity of the charge carriers.

Static charge can create problems in powder handling because electrical forces influence how particles interact with equipment and with one another. Charged material may accumulate on the walls of a hopper, conveyor or filling device, while interactions between particles can affect their distribution and movement. Such behaviour can contribute to unstable feeding and cleaning requirements during manufacture.

Food powders also exhibit mechanical and chemical interactions that are separate from electrostatic effects. Moisture content, particle size distribution, fat composition and surface properties can all affect flow behaviour and the formation of agglomerates. Reducing unwanted electrical charge would therefore address only one possible contributor to clumping, rather than providing a universal solution for every powder formulation.

RMIT’s researchers have identified protein powders, coffee and chocolate malt powders as possible future applications. These materials can experience static charging during mixing, transfer, filling and pouring. Whether electric-field control could improve those operations depends on the characteristics of the powder and its interactions with industrial processing surfaces.

Applying the laboratory technique to moving particles would require a different arrangement from the one used in the published experiments. A production system would need to control the relevant field during contact between material and equipment, while maintaining suitable conditions as particles travel through the process. The voltage, electrode configuration and behaviour of the particles would all require investigation.

Peter Sherrell has discussed the possibility of adapting electric fields around conveyors according to the material being handled. That example describes a future application of the research rather than equipment already demonstrated to work in a food factory. The reported experiments applied the field during contact and measured the resulting charge afterwards; real-time switching during industrial processing remains unproven.

Further development would also need to consider equipment safety and hygiene. Electrical components introduced near powders must be designed for the intended operating environment, and processing equipment used around food requires suitable cleaning and contamination controls. The latest results do not provide a qualified food-contact surface, a commercially installed conveyor system or a complete specification for a powder handling machine.

Environmental conditions may affect the behaviour of an industrial application. Humidity, temperature, surface wear and changing material composition can influence the accumulation or dissipation of static charge. A control method that works consistently with selected laboratory plastics would need further testing before similar performance could be assumed across food ingredients and different equipment materials.

The scientists also identify potential applications in plastics processing, electronics and filtration systems. In these areas, controlled surface charge could affect where particles adhere or how materials separate during handling. The potential benefits vary by process, and the reported study does not provide independently measured manufacturing savings or operating improvements in any of those industries.

The research provides experimental evidence that electric fields can influence charging during contact and separation between polymer surfaces. The next steps for food processing would involve testing actual powders, establishing suitable operating conditions and determining whether the effect can be maintained on continuous production equipment. No reduction in food-powder clumping, change in factory throughput or commercial equipment deployment has yet been demonstrated.