Hydrophobic kaolin-chitosan based coating for Spring frost protection

Crops protection against Spring frost has become increasingly crucial in recent years due to climate change. With regard to the process of ice formation during frost events, the application of a hydrophobic coating to plants could prevent injury. In this study, we present a new highly hydrophobic, biocoating based on kaolin clay, chitosan and stearic acid. High hydrophobicity was achieved by combining stearic acid with kaolin particles in ethanol under mild conditions. Several analytical techniques were used to study the structure and composition of the hydrophobized material and showed that the stearic acid was covering the kaolin particles through just interactions and not via covalent ester links. This hydrophobic material was then formulated with chitosan to produce coatings capable of preventing ice formation on plants by limiting the presence of ice nucleator and liquid water on buds and leaves. Increasing the proportion of chitosan decreased the overall hydrophobicity of the coating, while reducing its residence time on the leaves and increasing its mechanical properties. The most hydrophobic coating was obtained with the lowest chitosan ratio with a water contact angle up to 149 degrees. The coatings showed in vivo antifreeze efficacy of 1 degrees C below the critical freeze point of Phaseolus vulgaris beans in a convective freezing chamber.