Effect of carboxymethylated cellulose nanofibril concentration regime upon material forming on mechanical properties in films and filaments

Abstract

It is predicted that the forest and materials from the forest will play an important role to enable the transformation from our linear present to a circular and sustainable future. Therefore, there is a need to understand the materials that can be extracted from the forest, and how to use them in an efficient manner. Here, carboxymethylated cellulose nanofibrils (CNF) from the forest are used to produce films and filaments with the aim to preserve the impressive mechanical properties of a single CNF in a macro-scale material. The mechanical properties of both the films (tensile strength of 231 MPa) and filaments (tensile strength of 645 MPa) are demonstrated to be maximized when the starting suspension is in a flowing state. This is a new insight with regards to filament spinning of CNF, and it is here argued that the three main factors contributing to the mechanical properties of the filaments are (1) the possibility to produce a self-supporting filament from a suspension, (2) the CNF alignment inside the filament and (3) the spatial homogeneity of the starting suspension. The results in this study could possibly also apply to other nanomaterials such as carbon nanotubes and silk protein fibrils, which are predicted to play a large part in future high performing applications. Graphic abstract

Spinning of Stiff and Conductive Filaments from Cellulose Nanofibrils and PEDOT:PSS Nanocomplexes

“…In the acidic bath, the charge-stabilized CNFs are destabilized by the low pH in the bath, which leads to a protonation of the carboxyl groups of the CNF, which then associates due to the attractive van der Waals forces to form a gel filament. 28,35 Filaments were spun through a conical converging nozzle using a Nexus 6000 syringe pump into a flowing bath. The PEDOT:PSS/ CNF codispersion was injected at a rate of 0.5 mL/min into a pH 2 water bath.…”

“…The filament spinning technique relies on the extrusion of a stable dispersion of CNFs through a nozzle into a coagulation bath (Figure a). In the acidic bath, the charge-stabilized CNFs are destabilized by the low pH in the bath, which leads to a protonation of the carboxyl groups of the CNF, which then associates due to the attractive van der Waals forces to form a gel filament. , …”

Understanding ion-induced assembly of cellulose nanofibrillar gels through shear-free mixing andin situscanning-SAXS

“…2D films in photonic applications 16 . The main advantage of CNFs, are their inherent ability to form volume-spanning networks at very low concentrations [17][18][19][20][21][22] , making them highly desirable as building blocks in membranes, barriers, aerogels, foams 1,2,4 , 3D-printed materials 23 and also for making filaments that can be used for reinforcing new biobased composites and high-performance textiles 22,[24][25][26][27][28][29][30][31][32] The properties of materials produced from the bottom-up reassembly of CNCs and CNFs are highly dependent on their spatial and orientation distributions within the material, which in turn are set by the processing conditions 14,29 . A common route for controlling the nanostructure of the final product includes hydrodynamic alignment with subsequent assembly (transition from dispersion to gel, i.e.…”

The Effect of Ionic Strength and pH on the Dewatering Rate of Cellulose Nanofibril Dispersions

“…For complete isolation and the possibility to form homogenous networks the nanocellulose qualities need to be prepared below the network concentration (Geng et al 2018;Nordenström et al 2017;Håkansson 2021). If the starting concentration is too high, particle ocs are formed, resulting in inhomogeneous material distribution and reduction in material properties, e.g.…”

“…If the starting concentration is too high, particle ocs are formed, resulting in inhomogeneous material distribution and reduction in material properties, e.g. strength of lms (Håkansson 2021). Due to the high aspect ratio of CNFs this demands material formation often below 1 wt%, generally between 0.1 to 0.2 wt% (Håkansson 2021), requiring subsequent removal of a lot of water.…”