Polymers are essential in modern food packaging thanks to their low cost, light weight, flexibility, and chemical stability. They provide a crucial barrier to protect food from moisture, oxygen, sunlight, and microorganisms that cause spoilage and health risks. Among them, polyethylene terephthalate (PET) is especially valued for its transparency, stability, and strong mechanical properties.
However, conventional PET and other low-cost polymers have limitations in surface properties such as wettability, adhesion, and resistance to microbial growth. By treating polymers with cold plasma and incorporating nanoparticles (NPs), such as zinc oxide (ZnO), it can improve the polymer’s antimicrobial activity, transport properties, biodegradability, and UV protection.
Our team of scientists from the Group for plasma and laser applied research, in collaboration with partners, developed a simple method to synthesize PET/ZnO composites using commercial PET foils! This study was recently published in Applied Surface Science Advances.
The process involves treating commercial PET foils with a atmospheric pressure plasma jet (APPJ), coating them with ZnO nanoparticles, and repeating the plasma treatment to firmly embed the particles into the surface. This creates a unique two-dimensional nanoparticle incorporation that enhances PET’s performance where surface properties are critical, such as antimicrobial activity.
To produce the ZnO nanoparticles, the researchers used pulsed laser ablation in water, ensuring high purity. Atomic force microscopy (AFM) revealed that plasma treatment etched the PET surface, increasing its roughness from 6 nm to 13 nm and creating a more homogeneous nanoparticle distribution.
Crucially, leaching tests confirmed that nearly all Zn remained securely embedded in the PET surface, a key factor for performance, environmental and human safety, and sustainability. Additionally, the enhanced PET foils showed up to 29% improvement in UV protection, which helps to preserve food quality over longer periods and extend shelf life. While plasma treatment reduced PET’s elasticity, adding ZnO nanoparticles in the range of 200–500 μL reinforced the material.
Most strikingly, at the highest ZnO concentration tested (245.75 mg Zn/kg PET), the composites achieved nearly 100% antibacterial efficiency against Escherichia coli and Staphylococcus aureus.
“The results highlight the effectiveness of our composite synthesis method by showing strong antimicrobial properties against both bacterial strains! Importantly, the leaching test confirmed that the NPs are securely embedded in the PET surface, demonstrating the potential of these antibacterial surfaces for applications in the packaging industry”, concludes Rafaela Radičić, the first author on the published study.