Water-resistant properties improvement of aluminium oxide nanoparticles treated kraft paper by sparking process

This study aims to improve the hydrophobicity of non-sizing Kraft paper (KP) surfaces using nanoparticle coating through the sparking process. The aluminium oxide nanoparticles (Al₂O₃ NPs) were used for surface modification on KP through the sparking process, optimizing with varying sparking cycles (5–20 times), annealing temperatures (60–120 °C), and annealing times (1–3 h). Then, the Al₂O₃ NPs treated KP were examined by XRD, FT–IR, SEM, EDX, and AFM, respectively. The water contact angle (CA) was used to examine the water-resistant properties of the treated KP. The treated KP with varying sparking cycles up to 15 times showed higher surface coverage and enhanced fine roughness surface on the treated KP. The fine roughness surface of KP induced hydrophobicity (126° of CA) on the surface of KP at 15 sparking cycles. Similarly, the higher CA for hydrophobicity surface on treated KP from varying temperatures and times of the annealing process was demonstrated at 120° for 3 h. Therefore, the treated KP with 15 times of sparking cycle, annealing temperature at 120 °C for 3 h was defined as the optimized condition in this work. Furthermore, the developments of hydrophobicity and superhydrophobicity on the treated KP with CA at 135 and 155° were observed for the non-sizing and sizing KP, respectively. This indicated that the increased surface roughness and reduced surface energy of the treated KP simultaneously delayed the water absorption times on the KP surface. Consequently, the nano-treating of Al₂O₃ NPs using the sparking process shows the promising feature of inducing superhydrophobicity on the KP surface, which can produce a water-repellent corrugated box as an alternative packaging material.