With the improvement of the quality of life, people's demand for fruits and vegetables not only stays on the quantity, but also has a higher pursuit of freshness, nutrition and safety, which has promoted the unprecedented development of global food packaging. Traditional food preservation methods include cold chain preservation and controlled atmosphere storage [1]. Unfortunately, these methods are not only expensive and ineffective, but also seriously affect the appearance, texture, and taste of the food. Currently, petroleum-based packaging films are widely used due to their low cost and good mechanical properties. However, the energy crisis caused by non-renewability and the environmental pollution caused by non-degradability have brought huge problems and troubles to human beings. Hence, there is an urgent need to develop biodegradable and environmentally friendly materials to replace petroleum-based plastics for extending the shelf life of the food. Biologically sourced materials are considered as alternatives to petroleum-based packaging films due to their sustainability, excellent biodegradability, and biocompatibility. Examples include polysaccharides (cellulose, starch, chitosan), proteins (filamentous fibrous proteins, collagen, gelatin), lipids and other natural biopolymers [[2], [3], [4]]. Cellulose, the most abundant renewable and biodegradable resource on earth, contains hundreds of billions of tons in plants grown globally each year, exceeding the total existing oil reserves. This makes it the most promising candidate for replacing petroleum-derived plastics [5]. CNF are fiber aggregates with diameters <100 nm and lengths reaching the micron level. They have a large aspect ratio (around 70) and a high specific surface area (about 150 m2/g) [6]. CNF combines the properties of both cellulose and nanotechnology, retaining biocompatibility, degradability, high strength, high crystallinity, high specific surface area, and optical clarity [7,8]. The alternate structures of CNF include crystalline and amorphous regions, The crystalline region provides mechanical robustness and high thermal stability, while the amorphous region results in flexibility. The high aspect ratio of CNF, enriched with hydroxyl groups, forms strong hydrogen bonds between each nanofiber, giving CNF unique properties, including higher mechanical strength and gel-like properties.

This makes CNF an ideal material for nanocellulose films—strong, lightweight, and bio-based. However, due to its poor optical and film forming properties, CNF is often combined with other biopolymers (e.g., chitosan, alginate, cellulose derivatives) for applications in food packaging [5], biomedical [9], water purification [10] and flexible electronics [11,12]. CMC is a water-soluble carboxymethylated derivative of cellulose. It was used as a filler for CNF due to its good film-forming property, high optical transparency and chemical stability. To enhance food preservation, scientists have loaded the composite film with antibacterial and antioxidant bioactive agents, including tea polyphenols, tannin, curcumin, cinnamaldehyde, etc. [[13], [14], [15], [16]]. As the most abundant and widely studied natural functional components in tea, tea polyphenols have unlimited potential in the development of functional foods because its rich phenolic hydroxyl groups result in high antibacterial, antioxidant and anti-ultraviolet properties [17]. This enables the development of a green, non-toxic, degradable and antibacterial bioactive food cling film that extends the freshness and life of food. Active packaging represents an innovative food packaging strategy and a concept that responds to actual market needs.

In this study, CMC was used as the polymer matrix combined with CNF, and a certain thickness of nano-composite mold was prepared by solution casting method. This strategy not only addressed the performance defects that prevent the separate application of these materials, but also took advantage of their complementary optical properties. To enhance the functionality of the packaging, we optimized the mechanical properties by incorporating Gly and GA, resulting in high tensile strength and excellent malleability. Testing procedure for mechanical property displayed in Scheme 1(d). Additionally, we introduced antibacterial agents (TPs) to extend the shelf life of food. Just as Scheme 1(a) (c) showed the preparation process of nanocellulose composite films and the interfacial bonding mechanisms between all molecules respectively. Molecular mechanism of TPs for food preservation was demonstrated in Scheme 1(b). Finally, we explored the potential for rapid degradation within a short time through soil burial, water flushing and immersion. Scheme 1(e) illustrated the degradation of the film. The development of Nanocellulose Composite Films presents a promising avenue for the creation of sustainable and environmentally friendly packaging materials in the food industry.