Coupling fiber cationization with hygroplasticization for 3D-formable cellulose-based materials

Thanks to their high availability, renewability, and degradability, paper-based materials are promising candidates for partial replacement of less sustainable fossil-based products. A disadvantage of conventional paper is, however, its low strainability and restricted shapeability. Partial chemical modification of the fibers that constitute the paper, along with external plasticization, could alleviate this shortcoming. In this contribution, partial cationization of lignocellulosic fibers is employed to enhance the strength and strainability of handsheets; the extensibility is further improved by a moisture-induced plasticization. This combination of modification and hygroplasticization resulted in a strainability of 12%, allowing restraint-dried sheets to be formed into simple 3D structures. Dynamic vapor sorption, dynamic mechanical analysis, and small-angle X-ray scattering measurements are employed to gain deeper insight into the molecular and supramolecular mechanisms underlying the potential for 3D structuring of the papers. It can be concluded that cationization enhances the material’s moisture sorptivity. This is explained by increased accessibility of the fiber wall upon modification (as evidenced by decreased crystallinity and fibril separation) and by hydration of the functional groups. Moisture sorption is an enthalpically driven, highly exothermic process that results in softening of the material. It can be established that while cationization does not significantly affect the material’s temperature response, it does significantly affect its moisture response. Cationization lowers the onset for the fiber material to be softened by moisture, presumably explaining the extended strainability observed for the cationized, hygroplasticized material. Graphical abstract showing, from left to right; the concept for cationization and hygroplasticization—the material’s response at a nanolevel—the material’s macroscopic response, mechanical properties and potential of 3D forming).