Hydrophobic film based on bacterial cellulose from fermented banana pseudostem juice and coconut water with carnauba wax coating

Abstract

This study presents the development of hydrophobic polymeric films from bacterial cellulose (BC) produced by fermenting banana pseudostem juice and mature coconut water, two underutilized agricultural byproducts. Carnauba wax was applied as a surface coating in 1–3 layers, with and without hot pressing. The coating substantially increased hydrophobicity, with water contact angles rising from 56° in the uncoated film to over 100° in multilayer-coated films, although the films did not exhibit oleophobic behavior based on silicone oil contact angle measurements. The coating also significantly reduced water absorption from 91.45% in the uncoated film to 10.37% and 5.63% in the coated and coated–hot-pressed films, respectively, while water holding capacity decreased from 86.28% to 57.70% and 54.36%. Hot pressing produced a smoother and more homogeneous surface morphology, as observed by SEM. ATR–FTIR analysis supported the increase in hydrophobicity through reduced O–H and H–O–H band intensities. XRD analysis confirmed that the cellulose I crystalline structure remained intact after coating, while additional peaks corresponding to crystalline carnauba wax were observed. DSC revealed a melting transition of carnauba wax around 52°C, with hot-pressed samples showing an additional higher-temperature melting event. TGA indicated reduced moisture uptake but lower thermal stability, with degradation onset decreasing from 267°C in the uncoated film to 200–212°C in coated samples. Overall, multilayer carnauba wax coating provides a simple, solvent-free approach to improve the water resistance of BC films while preserving their structural integrity, making them promising for moisture-sensitive food packaging applications.