The Topochemistry of Cellulose Nanofibrils as a Function of Mechanical Generation Energy

Nanofibrillated cellulose (NFC) has garnered significant attention as a sustainable biomaterial, but its chemical reactivity with respect to its generation, i.e., fibrillation, has heretofore been unexplored. We prepared NFC samples with varying levels of fibrillation by controlling mechanical energy followed by acetylation as a probe to explore chemical reactivity. The degree of substitution (DS) reached a global maximum after which, surprisingly, it dropped to lower values at higher fibrillation or higher input (generation) energies. This behavior was attributed to two factors: the presence of higher bound water molecules at fibrillated surfaces, which hinder accessibility to cellulose chains, and enhanced self-aggregation of surface hydroxyl groups of NFC due to formation of hydrogen bond at higher fibrillation. Discovery of these two mitigating factors provide a promising physico-chemical strategy for efficient and sustainable production and modification of NFC to optimize performance for different ap...