Enhancing Starch-Based Food Packaging Films: Synergistic Effects of N-Isopropylacrylamide and Chitosan on Hydrophobicity and Antimicrobial Performance

This study presents an innovative approach to developing biodegradable food packaging by synthesizing a starch-based film with enhanced water resistance and antimicrobial properties. To achieve this, starch (ST) was chemically modified through an additive reaction with N-isopropylacrylamide (NIPA) and subsequently blended with chitosan (CS), improving its hydrophobicity and antimicrobial properties. The structural and chemical interactions within the modified film were characterized using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), confirming the successful integration of these components. The modification of starch ST with NIPA via a Michael reaction effectively reduced the film’s moisture sensitivity by substituting hydroxyl groups, leading to improved hydrophobicity. This enhancement was reflected in a significant increase in the contact angle from 44.79° for the pure ST film to 77.95° for the ST-37.5% NIPA/CS blend, along with a reduction in water vapor permeability (WVP) from 1.95 × 10^–10 g·cm/(cm²·s·Pa) for the pure ST film to 1.11 × 10^–10 g·cm/(cm²·s·Pa) for the ST-37.5% NIPA/CS film, demonstrating enhanced moisture barrier properties. Additionally, the ST-NIPA/CS film exhibited superior mechanical properties, including a tensile strength (TS) of 11.27 MPa and an elongation at break (EAB) of 185.92%. Notably, the films demonstrated strong antibacterial activity against Escherichia coli and Staphylococcus aureus, with inhibition zone diameters of 7.62 and 10.25 mm, respectively. The ST-NIPA/CS film effectively extended the shelf life of fresh-cut apples, achieving a decay index of 30.5% and a weight loss of 3.11% after 4 days, highlighting its potential as a sustainable packaging material.