Covalent Bioincorporation of Chitosan Nanoparticles Containing Eucalyptus and Lavender Essential Oil on Cotton Fabrics

Cotton is one of the most used fibers in the textile sector but is highly prone to microbial growth. Surface functionalization of cotton fabric is an alternative to overcome this problem and grant new properties to this product. This work aimed to develop a new methodology for the surface functionalization of cotton fabric, carrying out bio-oxidation catalyzed by laccases followed by the covalent incorporation of chitosan nanoparticles (CHINPs) containing eucalyptus or lavender essential oil to obtain fabrics with antibacterial properties. The cellulose bio-oxidation process was optimized considering the types of laccase and mediator used. The optimal conditions consisted of using laccase from Pleurotus ostreatus, TEMPO as a mediator, and a post-treatment with 1 mol L⁻¹ of a NaOH solution. CHINPs were synthesized using the oil-in-water emulsification method followed by ionic gelation. The characterization of the CHINPs confirmed the formation of spherical nanoparticles with diameters ranging from 12 to 40 nm and the presence of encapsulated lavender (12.5%) or eucalyptus essential oil (31.2%). The CHINPs were incorporated into the fabric by reacting the NH₂ groups of chitosan with the COOH groups of the bio-oxidized cellulose, generating a covalent bond. The antibacterial assay with E. coli and S. aureus indicated a reduction in bacterial growth in fabrics functionalized with nanoparticles compared to the non-functionalized one. Furthermore, the CHINPs and essential oils remained on the cotton surface even after at least five washing cycles, showing the effectiveness of the binding of the nanoparticles to the fiber surface.