A comparative study of the rheological properties of three different nanofibrillated cellulose systems

The rheological properties of NFC systems in different conditions are of important for their handling and implementation in various industrial applications. In this investigation, the existence of wall-slip effects and the rheological characteristics of three different nanofibrillated cellulose (NFC) systems - enzymatically pre-treated (NFCEnz), carboxymethyl cellulose grafted (NFCCMC) and carboxymethylated (NFCCarb) - were investigated. It was found that the rheological properties of NFCCarb are less affected by wall-slip effects when geometries with serrated surfaces are employed. The other systems showed, however, different degrees of susceptibility to these effects. The thixotropic properties of the different NFC systems, together with the impact of ambient ionic strength and temperature on the rheological properties of the systems, were also studied. It was found that the different systems displayed different rheological behaviours. In short, all systems regained most of their original properties as soon as severe shearing was ceased. The apparent viscosities of NFCEnz and NFCCMC were found to be little affected by the ionic strength of the system. However, the viscosity of the systems decreased somewhat with increasing temperatures. The viscosity of NFCCarb decreased on the other hand with the increasing ionic strength, but otherwise showed little sensitivity towards the ambient temperature. Hence, it was concluded that the rheological properties of NFCCarb were primarily governed by the electrosteric interactions between the NFC entities rather than the viscous properties of the liquid phase.