Characteristics of concentrated lignocellulosic nanofibril suspensions

Lignocellulosic nanofibrils (LCNFs) are usually isolated from biomass with concentration less than 2.0 wt%. The low concentration limits the transportation and end-use applications of LCNFs. Therefore, the development of concentration process and the characteristics of concentrated LCNF become desirable and important for commercial deployment of LCNF application. In this study, 1.0 wt% LCNF suspension was prepared by mechanical fibrillation using a supermass grinder after enzymatic pretreatment, and then dewatered to solid concentrations of 5.9 wt%, 16.3 wt% and 25.9 wt% by a centrifuge. The un-concentrated LCNF suspension was obviously stable, being translucent, and well dispersed in water, while the concentrated LCNF suspensions exhibited the gel-like behavior or “solid-like” behavior depending on the concentration. Bundle-like fibrils were observed for the concentrated LCNFs, and average diameter of concentrated LCNF became large but still less than 100 nm. Un-concentrated and concentrated LCNFs had similar crystallinity and crystallite size, and the morphological changes were mainly in the amorphous regions of the fibrils. The concentrated LCNF films still had relatively good UV-blocking property, water absorption and oxygen permeability. The increasing basis weight of films was benefit for enhancing the surface smoothness of films and interweaves between fibrils, resulting in the tensile index and specific modulus of films higher than 71.7 kN·m·kg⁻¹ and 6.8 MN·m·kg⁻¹, respectively. In sum, the concentration process affected the morphology structure of LCNF, but the concentrated LCNF still kept relatively good properties. Concentration process of LCNF suspension may be a feasible strategy for large-scale LCNF production and storage.