Optical and mechanical properties of nanofibrillated cellulose: toward a robust platform for next-generation green technologies

Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in Nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. To elucidate the optical and mechanical stability of nanofibrillated cellulose as a standalone platform, herein we report on three main findings: i) for the first time an experimental determination of the optical band gap of nanofibrillated cellulose, important for future modelling purposes, based on the onset of the optical band gap of the nanofibrillated cellulose film at Eg~ 275 nm (4.5 eV), obtained using absorption and cathodoluminescence measurements. In addition, comparing this result with ab-initio calculations of the electronic structure the exciton binding energy is estimated to be Eex ~ 800 meV; ii) Hydrostatic pressure experiments revealed that nanofibrillated cellulose is structurally stable at least up to 1.2 GPa; iii) Surface elastic properties with repeatability better than 5% were observed under moisture cycles with changes of the Young modulus as large as 65%. The results obtained show the precise determination of significant properties as elastic properties and interactions that are compared with similar works and, moreover, demonstrate that nanofibrillated cellulose properties can be reversibly controlled, supporting the extended potential of nanofibrillated cellulose as a robust platform for green-technology applications.