RESUMO
Twin-screw extrusion (TSE) is a recent strategy used to prepare nanocelluloses at high solid contents. However, various aspects of the mechanism of disintegration and the role of fiber pretreatment remain to be elucidated. Oxidized cellulose fibers with carboxyl contents between 300 and 700 µmol·g-1 were extruded in the presence of polyvinyl alcohol (PVA) at a 80/20 (w/w) ratio, to produce high-consistency nanocellulose gels at 15 wt% solid content, ready for use in multiple applications. The influence of the origin of the pulps and the oxidation treatment on the efficiency of fiber disintegration was evaluated by porosity measurement. The rheological properties of the nanocellulose-PVA gels and the mechanical properties and transparency of the resulting nanopapers were studied as well. Combining TSE and rotor-stator dispersion or short sonication homogenization contributed to enhancing the fibrillation during extrusion, providing a method to increase the fraction of nanocellulose in a much less energy-consuming manner.
RESUMO
Twin-screw extrusion (TSE) is a rather recent method to produce cellulose nanofibrils (CNFs) at a high solid content under continuous feeding. Here, never-dried commercial eucalyptus pulp was used as starting material to produce CNFs by TSE after a chemical pretreatment to introduce carboxylic groups via TEMPO-mediated oxidation and carboxymethylation. Five samples with a carboxyl content ranging from 800 to 1300 µmol.g-1 were produced to explore how the carboxyl content affects the aptitude of cellulose fibers to be broken down to nanoscale. The properties of the resulting CNFs in terms of nanosized fraction, morphology and rheological properties were investigated. A critical carboxyl content of 700 µmol.g-1was a prerequisite for the successful conversion of cellulose fibers into a CNF gel by TSE, regardless the pretreatment method. The degree of swelling of the fibers was put forward to account for this critical parameter.
