Small scale rheological observation of high consistency nanofibrillar material based furnishes

Abstract

Nanotechnology allows development of new enabling technologies with broad commercial potential. Cellulose has also the potential to be the source for renewable materials, which can be made multifunctional and self-assembling at the same time displace many non-renewable materials including metal and ceramics. The potential application area includes high quality paper products, paper coatings, high-performance and sustainable composite. Nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFC) can be obtained by the mechanical breakdown of natural fibers. These materials have the potential to be produced at low cost in a paper mill and may give many novel properties to paper, paper coatings, paints, or other products. However, suspensions of these materials have a complex rheology even at low solids. To be able to coat, pump, or mix NFC at moderate solids, it is critical to understand the rheology of these suspensions and how they flow in process equipment. Only a limited number of reports have been published in the literature on NFC rheology at moderate solids. NFC was found to be a highly shear thinning material with a power law index of around 0.1. Oscillatory tests gave consistent results for the parallel-disk and other geometries. The complex viscosity, the storage and loss moduli, and the yield stress were determined for the range of solids. Basic rheological and dewatering properties of nanocellulose based high consistency furnishes were evaluated. Two different grades of nanocellulose, microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC) with different swelling properties were used. Both types of nanocellulose have a common challenge, namely strong interactions between the particles resulting in aggregation of individual particles. These inter-particle interactions together with the physical entanglements cause high viscosities of nanocellulose suspensions and furnishes, which together with high water bonding property affects processability.