Enhanced stability in antibacterial performance of thymol/polylactic acid films through grafting “liquid-like” PDMS brushes

Antimicrobial packaging has received extensive attention due to its significant role in ensuring food safety. However, direct contact between liquid foods and antibacterial surfaces often causes food residue and affects the release of antibacterial agents, ultimately deteriorating antibacterial performance. Here, we report a strategy to overcome this imperfection by grafting PDMS molecular brushes onto the thymol-loaded polylactic acid (PLA) films. The PDMS molecular brushes provide the surface with low adhesion to various food droplets (e.g., cola, milk, and vinegar). The sliding angles (SA) for these food droplets are all less than 30°. Meanwhile, it does not affect the release of the antibacterial agent (thymol). Based on these advantages, the film shows enhanced stability in its antibacterial properties, with bactericidal rates against E. coli and S. aureus reaching nearly 100%. The excellent antibacterial performance can be maintained even after contact with liquid foods, as evidenced by the nearly unchanged inhibition zones against E. coli and S. aureus (e.g., the diameter of the inhibition zone against S. aureus is slightly changed from 1.87 nm to 1.83 nm). Moreover, the optimal conditions to fabricate the film were also discussed in detail, such as the content of thymol, the alkaline hydrolysis time, the temperature and time for grafting PDMS molecular brushes. The work reports a strategy to guarantee stable release of the antibacterial agent through grafting PDMS molecular brushes onto packaging films, thereby effectively prolonging the shelf life of liquid foods.