Antibacterial Coatings on Cotton Fabrics Based on Rosmarinic Acid-Loaded Bio-Based Resin and Oxygen-Plasma Surface Pretreatment

The development of antibacterial cotton textiles is of considerable interest for applications in healthcare, hygiene, and protective materials, where limiting microbial proliferation on fibrous surfaces is essential. However, many of the finishing strategies currently reported for cotton rely on metal-based agents or multifunctional synthetic systems, which may raise concerns about environmental impact, uncontrolled release, and long-term durability. In this context, the use of naturally derived bioactive compounds, combined with surface activation methods, represents a promising route toward more sustainable antimicrobial coatings. In this study, cotton fabrics were functionalized with a commercial biobased acrylic resin that contained increasing amounts of rosmarinic acid, a plant-derived polyphenol with recognized antimicrobial activity. The effect of oxygen plasma pretreatment was investigated to assess whether surface activation could improve coating distribution, interfacial adhesion, and functional performance. Resin films and coated fabrics were characterized by infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy, while antibacterial activity was evaluated against Staphylococcus aureus and Escherichia coli. The results showed that plasma pretreatment promoted a more homogeneous distribution of the coating on cotton and qualitatively supported a more effective organization of the resin-based functional layer. The incorporation of rosmarinic acid modified the thermal behavior of the resin, indicating reduced chain mobility and more importantly the occurrence of interaction with the polymer matrix. The coated fabrics displayed marked antibacterial activity against S. aureus, whereas the effect against E. coli was more strongly dependent on rosmarinic acid content and coating uniformity. Overall, the study demonstrates that combining plasma surface activation with a biobased resin containing rosmarinic acid is a viable strategy for preparing metal-free antibacterial cotton coatings.