Hydrochromic wood biocomposites for humidity and moisture detection

Stimulus-responsive materials with smart detection of humidity and moisture have been attracting extensive attention in wooden products, including the potential of developing the next generations of intelligent transparent wood. In this work, a hydrochromic transparent wood (HTW) biocomposite with characteristics of responsive to humidity is developed by compounding the oxazoline molecules with the transparent wood. The uniform distribution of oxazoline molecules in the cell wall of the transparent wood biocomposite is observed via the X-ray micro-computed tomography. The relationships of process-structure-property of the HTW are extensively characterized through confocal fluorescence microscopy and scanning electron microscopy. The resulting HTW biocomposite also possesses favorable thermal stability and mechanical properties. Moreover, the hydrochromic transparent wood can realize stable switching colors under different humidity conditions due to the reversible opening or closing of the oxazine rings. The fingerprint detection and various shapes on the surface of HTW biocomposite are demonstrated in the wet condition. This study provides a promising strategy to combine the detection of environmental humidity function and wooden bioresource that could be extended to broaden applications in smart buildings, intelligent sensors, simulative detectors, and anti-counterfeiting identifications.