Durable Bio-Based Hydrophobic Recrystallized Wax Coatings.

Abstract

Bio-waxes derived from natural species are beneficial for preparing non-wetting surfaces. Herein, the wetting properties of recrystallized wax coatings extracted from three naturally occurring superhydrophobic species-, Lotus leaves, Bauhinia leaves, and Periwinkle flowers, are reported as a function of recrystallization time, temperature, pH of water, and impact pressure. Lotus wax coatings showcased nanorods similar to that of Lotus leaves, while Periwinkle and Bauhinia waxes could not replicate micro-/nanofeatures from their respective natural species. Lotus wax coatings exhibited water contact angles (WCAs) of ∼150°, roll-off angles (RAs) of ∼8°, and self-cleaning properties. On the contrary, both Periwinkle and Bauhinia waxes showed WCAs of only ∼110°. Nevertheless, all coatings demonstrated remarkable temporal stability over 180 days, retaining their hydrophobicity. They also exhibit excellent thermal stability up to 100 °C and chemical stability for pH variations from 2.6 to 11.5. Furthermore, they withstand the impact of 3000 water droplets without losing their hydrophobicity. All three wax coatings showed very low moisture absorption coefficients in the order Periwinkle (5.5 × 10^-4 wt %/day) < Bauhinia (6.75 × 10^-4 wt %/day) < Lotus (1.075 × 10^-3 wt %/day), making them highly effective for moisture resistant applications such as food packaging, protective wood finishes, etc.