Relationship between aspect ratio and suspension viscosity of wood cellulose nanofibers

Cellulose nanofibers (CNFs) with aspect ratios varying from 30-300 were prepared from wood by acid hydrolysis and mechanical disintegration. The length and width of the individual CNFs were measured from atomic force microscopy (AFM) images. The steady shear properties of the CNF suspensions were measured using cone-plate type and capillary rheometers to determine their intrinsic viscosities. Higher aspect ratio CNFs had larger intrinsic viscosity values. The predicted aspect ratios on the basis of rigid rod theory for the lowest aspect ratio CNFs corresponded well with our measured values. However, for higher aspect ratio CNFs, the predicted values did not agree with the experimental values. A comparison of the CNF intrinsic viscosities with other types of particles and polymers indicated that the CNFs are semi-flexible rods rather than rigid rods.