Polymers are widely used in food packaging because they are easy to process, lightweight, flexible, chemically stable at low temperatures, and cost-effective. A key role of food packaging is to protect products from environmental factors such as moisture, oxygen, and microbial contamination that can cause spoilage and health risks. Among these materials, polyethylene terephthalate (PET) is particularly important due to its high transparency, dimensional stability, and good thermal and mechanical properties.
However, many low-cost polymers exhibit inadequate surface characteristics, including low surface energy, limited wettability, poor adhesion, and unsuitable surface morphology. To overcome these limitations while maintaining desirable bulk properties, various surface modification techniques are employed. One promising approach is cold plasma treatment, which can introduce different functional groups onto the polymer surface depending on the gas used to generate the plasma. In combination with the incorporation of nanoparticles such as zinc oxide (ZnO), this approach can further enhance material performance by improving antimicrobial activity, gas transport properties, biodegradability, and UV protection.
In this research our team of scientists from the Group for plasma and laser applied research, in collaboration with partners, produced PET/ZnONP composites using a novel two-step process assisted by oxygen low-pressure plasma, enabling treatment of commercially available polymer films. This paper was recently published in Surfaces and Interfaces.
Commercial PET substrates were pre-treated with oxygen plasma in an industrial-scale system, allowing treatment over large surface areas, which is crucial for potential industrial applications. Following plasma activation, ZnO NPs were drop-coated onto the PET surface at varying concentrations. The ZnO NPs were synthesized using the pulsed laser ablation in water method, ensuring a clean and well-controlled synthesis process.
Oxygen plasma treatment significantly increased the hydrophilicity and roughness of PET surfaces (water contact angle reduced from 78° to 4°, roughness from 1.6 to 4.1 nm). After ZnO nanoparticle deposition, partial hydrophobic recovery occurred, while surface roughness further increased to 15.3 nm. XPS depth profiling detected Zn up to ~500 nm below the surface, indicating successful surface NP incorporation. Leaching tests showed minimal Zn release (0.45% after 24 h), indicating strong NP adhesion and suitability for food packaging. The PET/ZnO composite exhibited > 99.9% antibacterial efficiency against Escherichia coli.
Plasma treatment reduced oxygen permeability by 154 times, while ZnO incorporation maintained a 139-fold reduction and added antibacterial functionality. However, water vapor permeability showed no improvement after plasma treatment and after ZnO NPs incorporation water vapor permeability did not change drastically. As a result, the estimated shelf life increased from about 13 hours for untreated PET to 84 days for plasma-treated PET and 76 days for the PET/ZnO composite.
The method is scalable and uses commercially available PET films and industrial-scale plasma treatment, making the resulting composites promising, safe, and environmentally friendly materials for advanced food packaging applications.
The full publication can be found on: 10.1016/j.surfin.2026.108905