Developing Food Packaging with in Integrated Passive Daytime Radiative Cooling and Freshness Preservation

Traditional electric cooling, a major energy consumer in the food supply chain, results in substantial energy waste and environmental challenges. There is an urgent need for non-electric, zero-emission methods for low-temperature food preservation. Passive daytime radiative cooling (PDRC) food packaging offers a promising solution by leveraging radiative cooling, where a surface emits more heat as infrared radiation than it absorbs, achieving cooling without external energy. This project develops innovative food packaging using partially oriented cellulose nanofibrils (CNFs) as solar reflectors and SiO2 as a thermal emitter for PRDC, enhanced with TiO2 for freshness preservation. This research assesses the material's cooling performance, associated mechanisms, functional properties, including mechanical and barrier properties, and the preservation properties through the appearance, decay rate, weight loss, firmness, pH, titratable acidity, total soluble solids, and total anthocyanins of the strawberries. Films were developed using CNFs, SiO₂, and TiO₂ through mixing followed by the casting or different templating methods, including ice templating and antisolvent templating. Heat dissipation was evaluated via temperature differences between the environment and the material’s underneath cavity. Microscopic morphology was analyzed using field emission scanning electron microscope (SEM) to further explain how the fine of CNFs and its structure influence PDRC behavior, SEM mapping to prove that SiO2 and TiO2 were uniformly dispersed within the films, while Fourier transform infrared spectroscopy (FTIR) was used to identify polymer infrared absorption peaks and explain the connection between the ingredients and CNFs mixture. For the packaging functionality test, stress–strain behavior of the films was tested using a tensile testing machine to identify the films’ mechanical properties. The Kit test was conducted to evaluate oil resistance, and the water contact angle was tested to determine its water barrier properties. Through systematic optimization of material composition and processing, the ideal formulation was confirmed as 80% fine of 1 wt% CNFs with 4 wt% SiO₂ (total solids CNFs: SiO2=1:4) fabricated via antisolvent templating. This material achieved notable cooling efficiency due to high emissivity within the atmospheric transparency window (AW) of SiO2 and its hierarchical porous structure morphology aligned within the solar-scattering spectrum. The film achieved a 2.50℃ average temperature reduction during the daytime and an overall 2.03℃ average cooling. The effective networking and uniform dispersion of SiO2 within the CNFs mixture was confirmed by the FTIR and SEM-EDS mapping, respectively. The SEM images further proved that the hierarchical porous structure was formed by the antisolvent templating method in which all pore sizes were within the 400 - 2500 nm range for the most ideal solar scattering. The incorporation of TiO₂ into the optimized CNFs–SiO₂ formulation (total solids CNFs: SiO2:TiO2 =2:8:1) via the antisolvent templating method significantly improved the mechanical properties of the films. The enhanced tensile strength and stiffness, as evidenced by the nearly doubled Young’s modulus and tensile strength, indicate improved internal bonding and reinforced structural integrity, while maintaining acceptable ductility. The grease‑resistance performance was assessed by the Kit Number 4 grease resistance test (TAPPI T 559). The film demonstrated moderate oil resistance, successfully passing the Kit 4 rating. The food preservation test using strawberries strongly confirmed that the PDRC material, the CNFs+SiO2+TiO2 antisolvent templating method processed film, has promising practical utility as a food packaging material for food preservation during harvest before transfer to storage. The results of visual observation, decay rate, and weight loss all confirmed that the CNFs+SiO2+TiO2 antisolvent templating method processed film notably slowed down the spoilage and water loss of the strawberries. Firmness retention further proved its ability to decrease textural degradation. In terms of biochemical stability of the strawberries, the CNFs+SiO2+TiO2 antisolvent templating method processed film helped maintain higher levels of total titratable acidity and lower pH, which indicates that the film slows down the metabolic degradation. The results of total soluble solids and total anthocyanins further showed that the CNFs+SiO2+TiO2 antisolvent templating method processed film helped maintain a more stable chemical profile. These results highlight its potential as an advanced food packaging solution, especially under challenging storage conditions like high temperature outdoor environments or extreme heat wave conditions. Overall, the TiO₂-incorporated CNFs–SiO₂ film fabricated by the antisolvent templating method exhibited a promising balance of mechanical strength and functional performance. It showed better mechanical strength and food preservation capabilities due to its PDRC property. These results highlight its potential as an advanced food packaging solution.