Multifunctional nanocellulose enables robust UV resistance, hydrophobicity and antibacterial activity of polyamide 612 composites

Polyamide 612 (PA612) naturally shows hydrophilicity, limited UV resistance, and poor antibacterial performance, which restricts its use in advanced applications. To overcome these limitations, aldehyde-functionalized CNC was first prepared via sodium periodate (NaIO 4 ) oxidation, followed by the fabrication of a fully bio-based nanoparticle (CNC@PDA/CO) through a gradient self-polymerization strategy, which was subsequently incorporated into PA612 using a facile solution-casting process. Interestingly, with only 3 wt% nanoparticle content, the composites achieved a 1687% increase in ultraviolet protection factor (UPF), a water contact angle of 114.1°, and antibacterial zones of 4.3 mm and 4.2 mm against Escherichia coli and Staphylococcus aureus , respectively. These impressive multifunctional improvements result from strong interfacial interactions driven by covalent bonds and hydrogen-bond networks through Schiff base and Michael addition reactions. This work offers a scalable, sustainable, and high-performance method for developing bio-based PA612 composites, showing great potential for next-generation high-barrier and antimicrobial packaging materials.