Shape-recovering nanocellulose networks: Preparation, characterization and modeling

Development of strong cellulose nanofibril (CNF) networks for advanced applications, such as in the biomedical field, is of high importance owing to the biocompatible nature and plant-based origin of cellulose nanofibrils. Nevertheless, lack of mechanical strength and complex synthesis methods hinder the application of these ma-terials in areas where both toughness and manufacturing simplicity are required. In this work, we introduce a facile method for the synthesis of a low solid content (< 2 wt%), covalently crosslinked CNF hydrogel where Poly (N-isopropylacrylamide) (NIPAM) chains are utilized as crosslinks between the nanofibrils. The resulting net-works have the capability to fully recover the shape in which they were formed after various drying and rewetting cycles. Characterization of the hydrogel and its constitutive components was performed using X-ray scattering, rheological investigations and uniaxial testing in compression. Influence of covalent crosslinks was compared with networks crosslinked by the addition of CaCl2. Among other things the results show that the mechanical properties of the hydrogels can be tuned by controlling the ionic strength of the surrounding me-dium. Finally, a mathematical model was developed based on the experimental results, which describes and predicts to a decent degree the large-deformation, elastoplastic behavior, and fracture of these networks.

Automated summary

The development of strong cellulose nanofibril (CNF) networks is crucial for advanced applications, especially in the biomedical field, due to their biocompatible nature and plant-based origin. However, the lack of mechanical strength and complex synthesis methods restrict their application in areas that require both toughness and manufacturing simplicity. This study presents a simple method for synthesizing a low solid content (<2 wt%) covalently crosslinked CNF hydrogel using Poly (N-isopropylacrylamide) (NIPAM) chains as crosslinks. The resulting networks can fully recover their shape after various drying and rewetting cycles. X-ray scattering, rheological investigations, and compression testing were conducted to characterize the hydrogel and its components. The influence of covalent crosslinks was compared to networks crosslinked by the addition of CaCl2. Furthermore, a mathematical model was developed to describe and predict the large-deformation, elastoplastic behavior, and fracture of these networks to a considerable extent.