Relative permittivity estimation of wheat starch: A critical property for understanding electrostatic hazards

Wheat starch is a widely used material in the food, pharmaceutical and entertainment industry not considered hazard but recently associated to dust explosions during processing and handling. How an insulating starch grain is charged and how its ability to be polarized is affected by environmental conditions such as temperature, humidity and frequency? are fundamental questions that must be explored in order to understand the dust explosion phenomena. Here we investigate the dependence of temperature, humidity and low-frequency on the relative permittivity of wheat starch. We characterized starch at the micro and macro scales using atomic force microscopy-based techniques and capacitive planar sensor-based measurements respectively. The results show high values of permittivity (˜80) at the microscale (single starch grains) compared to the low values (10-20) at the macroscale (20 mg of wheat starch). The differences are attributed to the Maxwell-Wagner-Sillars interfacial polarization process on individual grains and potential charge exchange between grains. Permittivity is a critical property to investigate starch electrostatic hazards.