Water and humidity-induced shape memory cellulose nanopaper with quick response, excellent wet strength and folding resistance

Water-induced shape memory polymers (SMPs) are the desired candidates for the uses in the fields of surgical operation, smart textile, and aerospace. However, most of water-induced SMPs are non-biodegradable petroleum-based polymers, and a quick response to water of SMPs is usually accompanied with the loss of wet strength due to the over hydration. To address this issue, in this work, a water resistant cellulose nanopaper (CNP) was firstly prepared with the cellulose nanofibrils (CNFs) produced by formic acid hydrolysis, and then the obtained CNP was modified via immersing in chitosan (CS) for the preparation of a robust CNP with quick water and humidity responses. Results showed that the original shape of the modified CNP after folding could immediately respond to water ( < 3 s) and humidity ( < 10 min). This quick response of the modified CNP was due to the synergistic hydration of CS and CNFs network, and the presence of CNFs with ester groups could prevent the over hydration of the modified CNP. Furthermore, the strong interactions between CS and CNFs and the reduced defects of CNP after modified with CS endow the final CNP with excellent mechanical performance (particular for the robust folding resistance (over 1190 times) and high wet tensile strength (65 MPa)), high transparency, as well as good barrier properties and antibacterial properties. Hence, the resultant CNP has potential applications in the fields of surgical operation, smart textile, humidity sensor, and high-quality packaging.