Hydrophobic waxes in ivory nuts affect surface modification by atmospheric air plasma jet

Abstract

Ivory nuts, bioproducts from South American palms, possess a hard, water-insoluble, and microporous endosperm with a strong resemblance to elephant ivory. The nuts sustainable appeal made them popular as eco-friendly substitutes to ivory and, more recently, microbeads. However, their hygroscopicity and mannan composition impart susceptibility to deterioration by microbes and insects. Cold plasma treatment has been widely investigated as a clean and cost-effective procedure for seed disinfection and surface modification. Hence, in this work, ivory nut endosperm was treated by an air plasma jet to modify wettability. Plasma treated samples were characterized by the water contact angle, AFM, and Raman imaging. Water contact angle results presented an increase from (31.5 ± 8.7)º to (78.9 ± 5.4)º, demonstrating surface hydrophobization. This result was attributed to the modification of surface chemistry by migration and repolymerization of extractives promoted by plasma treatment. AFM results evidenced the formation of a heterogeneous layer containing lamellar features similar to plant epicuticular waxes. Besides, principal component analysis of Raman imaging results highlighted spectral contributions from wax, xylan, mannan, and lignin. These results demonstrate that atmospheric air plasma jets can be employed for ivory nut hydrophobization with no need for additional precursors, altering surface chemistry by crosslinking endosperm native substances.