Evaluating ultra-fine friction grinding for the continuous production of nanofibrillated cellulose

Nanofibrillated cellulose (NFC) has applications in many sectors, but economical production of large volumes with a minimized ecological footprint remains challenging. In this study, we have developed a new design to upgrade the Masuko Supermasscolloider from a traditional batch mode to continuous circulation. This upgrade includes a pump-controlled circulating system, an in-line viscosimeter for real-time measurement of cellulose suspension viscosity, and a power meter to monitor and evaluate the energy consumption of both the pump and the grinder throughout the process. These modifications address the limitations of scaling up NFC production, offering a more efficient and effective approach. We investigated the production of NFC from cellulose feedstock derived from miscanthus biomass under various conditions, including different initial cellulose concentrations (1 wt%, 1.5 wt% and 2 wt%) and processing volumes (15L and 25 L) at different grinding time (from 15 minutes to 120 minutes, with 15 minutes intervals). A systematic study on the effect of these processing conditions on the size distribution of NFC particles was conducted using an analytical centrifuge (Lumisizer). A prevalence of particles with equivalent hydrodynamic diameters between ~250 nm and ~300 nm was observed regardless of the processing conditions. Notably, in the context of large-scale NFC production, our approach demonstrated a 70% reduction in specific energy consumption by either increasing the processing volume from 15 L to 25 L and increasing the initial cellulose concentration from 1 wt% to 2 wt%. Additionally, we explored the application of produced NFC as nanofillers in nanocomposite packaging materials. Specifically, NFC particles processed at different grinding times were incorporated into a glycerol-plasticized carboxymethyl cellulose (CMC) matrix to form bio-nanocomposite films. We have found that particles obtained with longer grinding time did not lead to increased mechanical performance. This simplifies the NFC production process by reducing the need for prolonged grinding, thereby saving time and energy while maintaining the desired properties of the nanocomposite samples.