Eco-Friendly Cellulose Nanofibrils Designed by Nature: Effects from Preserving Native State

Cellulose nanofibrils (CNFs) show high modulus and strength and are already used in industrial applications. Mechanical properties of neat CNF films or CNF-polymer matrix nanocomposites are usually much better than for polymer matrix composite films reinforced by clay, graphene, graphene oxide, or carbon nanotubes. In order to obtain small CNF diameter and colloidal stability, chemical modification has so far been necessary, but this increases cost and reduces eco-friendly attributes. In this study, an unmodified holocellulose CNF (Holo-CNF) with small diameter is obtained from mildly peracetic acid delignified wood fibers. CNF is readily defibrillated by low-energy kitchen blender processing. The hemicellulose coating on individual fibrils in the wood plant cell wall is largely preserved in Holo-CNF. This "native" CNF shows well-preserved native fibril structure in terms of length (∼2.1 μm), diameter (<5 nm), high crystallinity, high cellulose molar mass, electronegative charge, and limited mechanical processing damage. The hemicellulose coating contributes mechanical properties and high optical transmittance for CNF nanopaper, which can otherwise only be achieved with chemically modified CNFs. The CNF nanopaper shows superior mechanical properties with a Young's modulus of 21 GPa and an ultimate strength of 320 MPa. Moreover, hemicellulose imparts recyclability from the dried state. Altogether, this native CNF represents a class of colloidally stable, eco-friendly, low-cost CNF of small diameter for large-scale applications of nanopaper and nanomaterials.