Multifunctional bagasse nanocellulose-based composite films reinforced by the synergy of phytic acid/tannic acid for fast-response breath monitoring sensors

Recently, there is significant interest in using film-based humidity sensors to monitor human breathing. However, there is a lack of cheap, sensitive, and sustainable biomolecule-based films that simultaneously possess ultraviolet (UV) shielding, water resistance, antioxidant, and antibacterial properties. Herein, a facile and green strategy was proposed to fabricate a degradable film from cellulose nanocrystals (CNC) derived from sugarcane bagasse, okra polysaccharides (OPs), tannic acid (TA), and phytic acid (PA). The CNC serve as a matrix, OPs were used to enhance the mechanical properties of CNC film, and PA and TA function as crosslinking agents. After optimizing the PA/TA ratio, the CNC/OPs/PA/TA (COPT) composite film exhibited excellent flexibility, UV- shielding, water resistance, antioxidant, antibacterial, and moisture-sensing properties. Notably, OPs, TA, and PA enhanced the mechanical properties of the CNC-based film, as confirmed by molecular dynamics (MD) simulations. A humidity sensor using the COPT film displayed good sensitivity, low hysteresis (1.82 %), and longterm stability (30 days) over a wide relative humidity range of 25-98 %. When attached to a transparent face shield, it was able to discriminate different states of human breathing, with short response and recovery times to exhalation (1.4 and 1.8 s, respectively). This study provides a new perspective on the practical application of natural biodegradable biomaterials in wearable sensing devices.