Grinding severity influences the viscosity of cellulose nanofiber (CNF) suspensions and mechanical properties of nanopaper

The extent of influence of ultrafine grinding on thermal, structural and rheological properties of cellulose nanofibers and mechanical properties of nanopaper was studied. Bleached Eucalyptus Pulp was used as a raw material for nanocellulose preparation where samples were collected every 5 passages (5, 10, 15, 20 and 25 passages) for analysis. TGA curves suggest thermal stability is decreased after 15 passages as surface area increased in homogenized samples. Moreover, intense defibrillation anticipated thermal degradation and gradually reduced cellulose degradation enthalpy in samples, as evidenced by TGA and DSC curves, thus suggesting fibers size reduction. The XRD crystallinity index does not vary with increased grinding. Finally, suspensions viscosity and nanopaper density showed strong influence over the mechanical properties of nanopapers as evidenced by DMA characterization. Increase in defibrillation resulted in fibers with enhanced tensile strain, toughness, and elastic modulus. However, fiber over-grinding affected this improvement, probably reducing electrostatic repulsion between fibers and resulting in less dense nanopapers.