Fabrication of Durable, Super-hydrophobic and Self-cleaning Wood Surfaces Based on ‎Silica-Carnauba‏‌ ‏Wax, Nano-hybrid‏ ‏coating into Epoxy resin matrix

 Surface modification and coating is one of the effective methods to increase the performance and service life of wooden structures. All kinds of super-hydrophobic techniques with a contact angle above 150 degrees and a sliding angle less than 10 degrees, in addition to creating high hydrophobicity, also improve the antimicrobial and other surface properties of the substrate. Nevertheless, resistance to mechanical and moisture damage are very important in connection with super-hydrophobic surfaces. Natural waxes are one of the efficient and healthy materials for creating a durable super-hydrophobic coating with high biocompatibility. In this research, nano-silica modified with non-fluorine alkyl materials in the presence of epoxy resin has been used to create superhydrophobic surfaces of birch wood (Betula pendula). Also, carnauba wax has been used to improve water repellency, self-cleaning property and durability in conditions of mechanical damage, humidity and harsh environments, comparatively.

Dodecyltrichlorosilane was used in the presence of toluene solvent for functionalizing and hydrophobicizing silica nanoparticles. A formulation containing 2% of modified nano silica and some epoxy resin was used by spray method to fabricate super-hydrophobic coating on birch wood. Also, the optimal amount of vegetable carnauba wax (Brazilian palm) was used as a reinforcing agent to make the nanohybrid formulation. Durability and stability to mechanical damage (sandpaper abrasion, water impact) and harsh environments (acidic, alkaline, ultraviolet rays and solvents) were investigated. Finally, the self-cleaning potential of the processed wooden surfaces was evaluated by qualitative (inclined surface) and quantitative (dropping) methods using edible liquids.

Both types of nanocomposite (without wax) and nanohybrid (containing wax) coatings caused the super-hydrophobicity on birch wood. The adding the optimal amount of carnauba wax to the epoxy-based nanocoating structure leads to a contact angle of 170 degrees and a sliding angle of less than 3 degrees by water drops. In addition, carnauba wax caused the stability and strength of superhydrophobic surfaces in aging and mechanical conditions. The highest level of stability in harsh environments was related to the hybrid nanocoating. The highest contact angle was observed for pomegranate juice and the lowest for milk. Also, the self-cleaning potential with various types of Fanta and Coca-Cola drinks on the superhydrophobic surface was successful.

The use of carnauba wax increased the contact angle and decreased the sliding angle. The use of carnauba wax significantly improved the mechanical properties and water-repellency of the super-hydrophobic coating. The chemical nature and morphological structure of wax in the coating is the reason for this superiority. The super-hydrophobic surface made with nanohybrid coating in the presence of carnauba wax has the potential of self-cleaning, biocompatibility and stability in service conditions and can be used to protect all types of general surfaces in the field of food, especially lignocellulosic substrates such as wood and paper.
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