High Solid Content Production of Nanofibrillar Cellulose via Continuous Extrusion

Cellulose nanofibrils (CNFs) with a high solid content of 10% were produced from oxidized holocellulose pulps by continuous extrusion using a twin-screw mini compounder in replacement of the high pressure homogenization or grinding, conventionally used to produce CNFs. A strong gel with high yield in nanofibrillated material exceeding 80% was obtained after 30 min of recirculation through the extruder at room temperature. The effect of the chemical composition of the pulp and the carboxyl content on the fibrillation yield and the properties of the ensuing CNFs were investigated. CNF material with a lateral dimension lower than S nm and a length within the micrometer scale was produced through this simple approach, and no evolution in crystallinity in terms of crystalline indexes was observed after prolonged extrusion up to 30 min. Dynamical rheology showed that the CNF suspension exhibited an elastic gel-like behavior over the whole concentration domains, ranging from 1 to 10% w/w. The described preparation method is easy to implement, without any clogging risk during the disintegration process and can be scaled up for a high capacity and cost-effective production of CNFs at high consistency.