INFLUENCE OF DISSOLVED MACROMOLECULES ON ADHERENCE OF PARTICULATE SOILS

Polysaccharides, proteins, lipids and other biopolymers are the main components of food and pharmaceutical mixtures and may influence interactions at interfaces and thus fouling and cleaning. In this study, quartz particles (10 to 30µm) were used as a model soil for examining the effect of dissolved proteins on the cleanability of substrates after soiling and drying. Glass and stainless steel pretreated by UV-Ozone (StSteel-UVO) were used as model hydrophilic substrates, while hydrophobic substrates were represented by stainless steel cleaned with ethanol (StSteel-Eth) and polystyrene. BSA and β-LGB were used as proteins. The quartz suspensions used for soiling (150g/L) were prepared in pure water and in a solution of each protein (8g/l). After soiling and drying, the cleanability was evaluated using a radial-flow cell, with pure water as the cleaning fluid.
When soiling was made with a quartz suspension in pure water, the soil adherence increased with substrate hydrophilicity. This may be explained by better droplet spreading and increase of the capillary forces created upon drying. The presence of proteins in the suspension used for soiling hydrophilic substrates (Glass and StSteel-UVO), decreased the adherence of quartz particles. Its effect was less marked and tended to be opposite for less hydrophilic substrates (StSteel-Eth, Polystyrene). The comparison of different substrates and two proteins showed that the adherence cannot be explained by a simple relation with the contact angle. Other factors may be the solution surface tension itself and the protein behavior at the interfaces created by drying and by rehydratation during cleaning.
When considering the influence of substrate on soiling, it must be kept in mind that high surface energy solids (metals, oxides) are readily contaminated in contact with air and lose their hydrophilicity. Amazingly this may improve the substrate behavior regarding cleanability with respect to particulate soil.