During the last two decades, nanosized cellulose nanofibrils commonly known as CNF or NFC (nanofibrillar cellulose) has emerged as one of the most promising nanomaterials derived from renewable natural resources and has aroused considerable academic and industrial interest. The nanoscale dimensions, biodegradable character, high potential bonding, high aspect ratio, lightweight, and sustainability are the driving force toward the use of CNF in a wide range of application in innovative nanostructured materials, highlighted in a number of recent reviews.
Currently the most widely used approache for the production of CNFs is high pressure homogenizer (HPH), microfluidize and Masuko grinding. Although all of the above reported processes were effective in breaking down cellulose to nanoscale and despite the commercial availability of the microfluidizer, grinder or the high pressure homogenizer at different scales, the widespread use of CNFs is still limited and below expectations. Three main obstacles are facing the large-scale production of CNFs. The first one is the high energy consumption involved in the production of CNFs when a high pressure homogenizer or a microfluidizer are used. Even though the chemical pretreatments contributed to notably reducing the energy input to less than 20 KWh/kg of dry CNF, this is still too high. The second obstacle is the low consistency of the CNFs produced via these disintegration modes. Typically, CNFs are produced at a solid content between 0.5 up to 2.5 wt% at maximum, which led to a large dilution effect when CNFs are used as an additive over 5% and contributed to increase the transport cost. The third issue is the high cost of the high-pressure homogenizer or the microfluidizer and their frequent clogging during the disintegration process.
Twin screw extrusion (TSE) which is commonly used for nanocomposites and composites processing, might be interesting alternative for the production of CNFs with high solid content ranging from 10
up to 25%. Although, this approach is not as popular as HPH, grinding or microfluidization, it is promising for the high consistency production of CNF with low energy demand.
The aim of the project is to investigate the production of CNFs at high solid content (between 10 to 15w.%) using twin screw extrusion for the disintegration of the pulp. The feasibility of the approach has been demonstrated recently in a work performed in the LRP using a laboratory scale co-rotating conical twin-screw mini extruder (TSE) DSM-Xplore 15cc Micro-extruder, comprised of a clamshell barrel with a conical twin-screw extruder. Using TEMPO-mediated oxidized fibers with carboxyl content around 500 µmol/g, it was possible to disintegrate the fibers into CNFs with high yield in nanofibrillated material exceeding 70% after continuous extrusion during 40 min by recirculation through the extruder.
Within this project, we would like to go further in exploring how the chemical pretreatment and the extrusion parameters in terms of the screw speed, the temperature and the presence of additive are likely to affect the extent of fibrillation and the rheological properties of the ensuing CNFs suspension.
This project involves a collaboration between the University of Sfax, the LRP and the LGP2 (Grenoble)
PI: Samir Boufi (visitor); Co-PI: Albert Magnin (LRP) & Naceur Belgacem (LGP2)