Furan-derived nanocrystalline cellulose as bio-filler for sustainable rubber composites

In recent years, nanocellulose (NC) has gained growing attention as a biobased material thanks to its high tensile modulus, large surface area, and complete renewability. Moreover, the NC surface can be chemically modified to tailor its properties, making it a promising filler in the development of sustainable composites and elastomers. Besides the replacement of traditional fillers, recycling of the polymer matrix is a key factor to composite/elastomer sustainability. Dynamic covalent polymer networks offer a solution by combining thermoset durability with thermoplastic reprocessability, exploiting different crosslinking strategies (i.e. Diels Alder). The present work describes the modification of cellulose nanocrystals (CNCs) to promote covalent and reversible interactions with a polymer matrix through a Diels-Alder reaction between furan and maleimide groups. In this perspective, different cellulosic materials (i.e., hemp pulp, powder cellulose, and microfibrillated cellulose) were treated with sulfuric acid to obtain CNCs. The extracted materials were then characterized by FT-IR spectroscopy, XRD, and TEM. Following this preliminary screening, hemp pulp was selected as the material of choice for further investigation. Two different strategies were then employed to graft furane moieties onto the CNC surface: one was based on reductive amination, and the other on a coupling reaction (Figure 1). These synthetic approaches required pre-treatment of nanocellulose with NaIO4 or TEMPO, to introduce aldehydes or carboxylic groups, respectively. The presence of furane in the final products was confirmed by both FT-IR and SS- NMR spectroscopy, while the oxidation degree of the intermediate products was estimated through titration. Preliminary tests were conducted to incorporate the functionalized CNCs into a reversibly crosslinked rubber matrix and the resulting materials have been characterized by DSC and DMA.