Three-Step Fully Enzymatic Strategy for Multi-Functionalization of Polylactic Acid (PLA) Nonwoven Fabric for Food Preservation and Its Biodegradability

Abstract To address the inherent inertness of polylactic acid (PLA) nonwoven fabrics and the challenge of balancing grafting efficiency with biodegradability in conventional functionalization strategies, this study proposes an enzymatic surface modification approach. First, a mild and limited enzymatic hydrolysis using proteinase K was employed to introduce carboxyl and hydroxyl groups as reactive sites on the surface of PLA fibers. Subsequently, laccase was used to first catalyze the formation of a uniform polydopamine (PDA) coating on the fiber surface, followed by the covalent grafting of ε-polylysine (ε-PLL). The results showed that limited enzymatic hydrolysis brought about a 40.3% relative improvement in the fabric weight-gain ratio originated from PDA deposition, alongside a 26.2% relative improvement for the fabric weight-gain ratio originated from ε-PLL immobilization, in comparison with the nonhydrolyzed PLA nonwoven substrate. The resulting PDA-ε-PLL@G-PLA nonwoven fabric exhibited improved mechanical properties, with the tensile strength increasing from 0.932 ± 0.048 to 1.154 ± 0.017 MPa and elongation at break increasing by 11.2%, respectively. The functionalized fabric also exhibited a DPPH radical-scavenging activity of 61.1% and antibacterial activity of >99% against Escherichia coli and Staphylococcus aureus. Blueberry preservation experiments demonstrated that this material significantly extended the shelf life of the fruit. The functionalized nonwoven fabric achieved an enzymatic degradation rate of 92.0%. This study provides a new approach for the green functionalization of degradable packaging materials.