Lysozyme-modified nanocellulose for enhanced nucleation and antibacterial properties in advanced polylactide composites

A novel two-step modification of nanocellulose using dicarboxylic acid followed by lysozyme functionalization was developed to enhance the performance of polylactide-based biocomposites. Different filler samples were synthesized under varying process conditions to determine the optimal conditions for functionalization with lysozyme. In each case, the formation of covalent bonds between the filler components was confirmed. A comprehensive evaluation of the fillers, examining their chemical and supermolecular structure, as well as their antibacterial properties, led to the selection of the most promising, two-step modified filler, which was subsequently incorporated into a polylactide polymer matrix. Additionally, biocomposites with nanocellulose or nanocellulose modified solely with lysozyme were prepared as reference materials. The findings reveal that the modification of nanocellulose with dicarboxylic acid and lysozyme, significantly improved the polymer's crystallization behavior, lowering the cold crystallization temperature, and inducing transcrystalline layer formation, which is indicative of enhanced nucleating activity. These improvements were achieved without compromising mechanical properties. Moreover, composites with lysozyme modified filler demonstrated antibacterial activity against gram negative bacteria, including Escherichia coli and Pseudomonas aeruginosa, with superior effectiveness against the gram positive bacteria Bacillus thuringiensis. In contrast, composites without lysozyme modified nanocellulose did not exhibit such antibacterial behavior. This study emphasizes the improved properties of polylactide composites enhanced with lysozyme-modified cellulose, presenting them as promising options for sustainable active packaging with controlled antibacterial agent release, offering potential applications in the biomedical field.