Enhancing Strawberry Freshness: Multifunction Sustainable Films Utilizing Two Types of Modified Carbon Nanotubes for Photothermal Food Packaging

Currently, antimicrobial films with stable and efficient antibacterial activities are receiving considerable attention in the food packaging industry. Herein, a chemically/physically linked konjac glucomannan-sodium alginate (KGM-SA)@carbon nanotubes (CNTs)/Fe³⁺ composite film with outstanding resistance to ultraviolet radiation, oxidation, and bacteria, as well as excellent photothermal effects and mechanical properties, was successfully prepared using a solvent flow method. Tannic acid-modified carboxyl-functionalized CNTs (TCCNTs), l-cysteine-modified carboxyl-functionalized CNTs (LCCNTs), and Fe³⁺ were incorporated into the prepared film. The film structure of KGM-SA@CNTs/Fe³⁺ was characterized using various methods, confirming the formation of a dual-cross-linked network through metal-coordination bonds and hydrogen bonding. This unique structure endowed the film with excellent water vapor permeability (3.58 g mm/m² day kPa), water resistance (water contact angle = 93.66°), and thermal stability. Further, the film exhibited outstanding photothermal conversion efficiency and stability under near-infrared irradiation (300 mW/cm²) as well as excellent bactericidal properties against <i>Staphylococcus aureus</i> and <i>Escherichia coli</i>, achieving a bacterial inhibition rate of >99%. In a strawberry preservation experiment, the KGM-SA@CNTs/Fe³⁺ composite film exhibited remarkable preservation effects, extending the shelf life of strawberries by 4-6 d. Thus, this photothermal antibacterial film offers a new approach for the application of CNTs in food packaging.