Bio-degradable superhydrophobic cellulose-based paper straws fabricated through coating of citric acid-crosslinking CNF & stearic acid.

To address the poor water resistance and mechanical degradation of conventional paper straws, this study develops an environmentally benign, fully biodegradable superhydrophobic coating using cellulose nanofibers (CNF), stearic acid (SA) and citric acid (CA). CNF was first dispersed in ethanol, followed by chemical grafting of hydrophobic alkyl chains onto its surface; a synergistic micro-nano hierarchical structure was then constructed by optimizing thermal soaking and drying processes. The hybrid material's morphology was comprehensively characterized via FTIR, SEM, and AFM. The resulting coating exhibited exceptional superhydrophobicity (water contact angle, WCA = 166°), effectively resisting liquid penetration and maintaining structural integrity under humid conditions. Mechanical tests showed 216 % higher tensile strength, 137 % improved compressive performance, enhanced abrasion resistance, and better water vapor barrier properties; notably, it retained 83.67 % of dry strength after water immersion and degraded rapidly in soil. The coating formulation was further engineered into a curcumin-loaded film, thereby adding a smart, visual pH-indication function for monitoring beverage freshness over 0-6 days. This multifunctional approach provides a viable bio-based alternative to petrochemical coatings, paving the way for next-generation eco-friendly disposable paper products.