An adapted dynamic stickiness test for powder starches response to temperature and relative humidity

In the drying and handling steps of food powders production processes, materials stickiness can affect the piping system, the equipment and the process performance. In order to avoid blockages and maximize the process yield, it is important to identify the parameters that play a role in the sticky behaviour of the powder, in order to keep it in a free-flowing state. In the case of powder starches, stickiness is especially evident in its impact on cyclone separators and in pipes, where particle deposition on the walls and surfaces is a common problem. The sticky behaviour of powder starches has not been thoroughly studied in terms of response to temperature and relative humidity, which are in fact the stickiness parameters. Starch stickiness is investigated through the adaptation of an existing dynamic stickiness test for food powders, followed by the evaluation of the impact of surface roughness, starch origin, temperature and relative humidity. The performed tests have first underlined a clear influence of the particles/surface impact angle between 30° and 60° and of the distance between 17 and 22 cm: a decrease of the former and an increase of the latter favour adhesion. Moreover, the stickiness of powder starches seems to be dependent on the temperature and moisture content, that cause the powder to switch to a highly sticky state if one or the other is increased up to a certain value. This trend is the same independently on the starch origin, that however plays a role in the entity of stickiness. Furthermore, a higher roughness of the deposition surface seems to hinder deposition at T = ˜53°C and between 41.9% and 56.3% RH. Further testing is required to explore the observed phenomena, but the obtained results can suggest on a general level possible solutions to reduce the negative impacts of starch stickiness on the production process yield. The main aim would be keeping the operating conditions in a range in which the material doesn’t show high stickiness.