Quaternized, cationically charged, cellulose fibers and cellulose nanofibrils (CNFs) are attractive candidates for the development of renewable materials. The increased research interest seen over the last decade is largely owing to such material’s strong interaction with water facilitating a completely new toolbox in the design of cellulose-based materials. Our research is focused on studying quaternized fibers and material built up from them, and in previous studies we have shown that quaternization enhances both strength and strainability of fiber-based material. The material hence shows a great potential to be used as a durable packaging material. 
It is commonly known that fiber-based materials are susceptible to sorb moisture from air, an attribute which can be considered both a blessing and a curse as softening, often connected to increased strainability, is achieved on the expense of the mechanical strength of the material. This work studies the moisture sorption of quaternized fibers. Structural changes in the material upon moisture sorption were captured by small angle X-ray scattering measurements, and by combining dynamic vapor sorption experiments with relative-humidity controlled dynamic mechanical analysis, it can be established how moisture sorption and hygroplasticization are connected to each other. Results show that the introduction of quaternary groups to cellulose significantly enhances the moisture sorption, which results in micro- and macroscopic structural changes of the material and a concomitant material softening. The stainability induced by quaternization of the fibers and the extended strainability achieved by hygroplasticization was used to prepare restraint-dried papers, as in conventional papermaking, that could be 3D-shaped into more complex structures than is feasible for traditional papers. The work thus not only study the moisture interactions and hygroplasticization of quaternized fibers and materials thereof but also showcases an approach to achieve a renewable, cellulose-based, material which can replace fossil-based materials in complex-shaped products.