Dual-crosslinked poly(γ-glutamic acid)/chitosan nanofiber composite films with enhanced wet mechanical stability

Abstract

Poly(γ-glutamic acid) (PGA) is a biodegradable microbial polypeptide with potential for sustainable film materials, but its strong hydrophilicity and swelling tendency limit its mechanical stability under wet conditions. Herein, we report dual-crosslinked PGA/chitosan nanofiber (CsF) composite films with improved water resistance, enhanced wet mechanical stability, and tunable degradability. PGA was modified with furan groups and covalently crosslinked with 4-arm poly(ethylene glycol) maleimide through a Diels–Alder reaction, while CsF served as a physical crosslinking domain through electrostatic interactions between its amino groups and the carboxyl groups of PGA. Notably, as the CsF content increased from 0 to 1.0 wt%, the mechanical strength of the composite films markedly improved. The optimized 1.0 wt% CsF film showed a dry tensile strength of 75.7 MPa, 8.7 times higher than that of the neat film, and retained a wet tensile strength of 4.3 MPa and a wet toughness of 1.12 MJ m⁻³ in the fully swollen state in deionized water. This wet-state robustness was further supported by a reduced equilibrium swelling ratio of 951% and an increased water contact angle from 25° to 85°. Moreover, the films exhibited complete degradation within 60 days in natural soil and 90 days in enzyme-containing artificial seawater. This work provides a feasible strategy for balancing wet mechanical robustness and degradability in PGA-based sustainable films.