Facile fabrication of arecanut palm sheath based robust hydrophobic cellulose nanopapers via self-assembly of ZnO nanoflakes and its shelf-life prediction for sustainable packaging applications

Cellulose nanofibers have been extracted from arecanut palm sheath fibers via mild oxalic acid hydrolysis coupled with steam explosion technique. Cellulose nanofibers with diameter of 20.23 nm were obtained from arecanut palm sheath fibers. A series of robust hydrophobic cellulose nanopapers were fabricated by combining the synergistic effect of surface roughness induced by the successful deposition of zinc oxide (ZnO) nanoflakes and stearic acid modification via a simple and cost-effective method. In this work, agro-waste arecanut palm sheath was employed as a novel source for the extraction of cellulose nanofibers. 2 wt% of ZnO nanoflakes and 1 M concentration of stearic acid were used to fabricate mechanically robust hydrophobic cellulose nanopapers with a water contact angle (WCA) of 134°. During the deposition of zinc oxide nanoflakes on the CNP for inducing surface roughness, a hydrogen bonding interaction is formed between the hydroxyl groups of cellulose nanofibers and the zinc oxide nanoflakes. When this surface roughened CNP was dipped in stearic acid solution. The hydroxyl groups in zinc oxide nanoflakes undergoes esterification reaction with carboxyl groups in stearic acid solution forming an insoluble stearate layer and thus inducing hydrophobicity on CNP. The fabricated hydrophobic cellulose nanopaper displayed a tensile strength of 22.4 MPa and better UV blocking ability which is highly desirable for the sustainable packaging material in the current scenario. Furthermore, the service life of the pristine and modified cellulose nanopapers was predicted using the Arrhenius equation based on the tensile properties obtained during the accelerated ageing studies. The outcome of this study would be broadening the potential applications of hydrophobic and mechanically robust cellulose nanopapers in sustainable packaging applications.