Sustainable lignocellulosic nanofibers-based films with sensitive humidity and pH response for UV-blocking food preservation

UV-induced photo-oxidation critically compromises food quality, necessitating advanced materials that simultaneously mitigate light degradation and enable real-time freshness monitoring. Here, the excellent UV-blocking films with sensitive humidity and pH response are developed by synergistically incorporating sodium ligninsulfonate-derived carbon quantum dots (L-CDs) via a simple microwave-assisted generation and light absorption of lignin from lignocellulosic nanofibers. The resulting films with hybrid structure can block 99.74 % (UV-C), 99.86 % (UV-B), and 87.90 % (UV-A) of radiation while maintaining 85.60 % visible light transmittance (600 nm), and has excellent mechanical strength (61.51 MPa). Under the protection of composite film, pork, strawberries and grapes all maintained longer freshness than unprotected controls. Profited from the protonation and deprotonation of L-CDs and the disconnection/reconstruction of hydrogen bonds, it shows sensitive humidity and pH response with changes in blue fluorescence. Furthermore, the conductivity of the composite film increases exponentially as the increase of humidity, showing excellent humidity response monitoring. As expected, the prepared composite film can detect changes in conductivity and resistance for monitoring the freshness of food. So, this work provides the development prospects for multi-functional composite films with UV-blocking and intelligent humidity & pH sensing for food preservation and intelligent monitoring.