Plant-Based Wax Crystallization for Fabricating Superhydrophobic Surfaces: Investigating Rice Bran, Sunflower, and Berry Waxes using Toluene and Hexane

Abstract

Superhydrophobic surfaces, which exhibit high water-repellent properties, have gained significant interest due to their versatile applications in energy efficiency for solar panels, anti-icing in aircraft wings, and anti-fogging in camera lenses. Plant-based waxes, derived from various plant parts, such as rice bran, sunflower, and berry waxes have been investigated in recent research for their potential utilization in skin care products and the food industry, owing to their presence in agricultural waste. However, a research gap exists in imitating their properties to produce hydrophobic surfaces. This study aims to maximize the water-repellent behavior of plant-based waxes through the crystallization technique which manipulates the surface morphology to create a hierarchical structure. The water-repulsive behavior is quantified through the measurement of the contact angle between the surface and water in contact. Two solvents, toluene and hexane, were selected to dissolve the waxes. During the crystallization process, three parameters, namely crystallization humidity, melting temperature, and concentration, were systematically varied and statistically analyzed using the MWU test. Results show that rice bran and sunflower waxes demonstrated superior superhydrophobicity. However, they exhibited poor adhesion to the soda-lime glass, and the quality of the sunflower wax coating was suboptimal. To address this, an annealing process was conducted at three different temperatures: 50°C, 60°C, and 70°C, resulting in significantly improved coating quality and adhesion as the temperature increased. However, there was a minor reduction in the contact angle, and this effect became more pronounced with higher annealing temperatures. Thus, a need to analyze the statistical significance of this reduction was conducted via ANOVA. To assess the practical applicability of the coatings, they were fabricated and tested on three substrates, including woven fabric, wood, and sponge, demonstrating the potential of these coatings as sustainable alternatives to current superhydrophobic surfaces.