Effect of wettability and surface free energy of collection substrates on the structure and morphology of dry-spun cellulose nanofibril filaments

Utilization of cellulose nanofibrils (CNF) for filament production is a comparatively new approach, which can broaden nanocellulose applications by providing continuous long filaments suitable for composite and textile applications. Methods are proposed for the spinning of filaments from cellulose nanofibril suspensions, which are mainly categorized into two groups, i.e. dry-spinning and wet-spinning. For the dry-spinning method, the substrate on which the filament is spun will have a significant influence on the properties of the filament because the as-spun CNF will initially contact it. In this work, the influence of different collection substrates on the properties of CNF filament was studied. Filaments with an average diameter of 0.1 mm were spun on different collection substrates including Teflon tape, Teflon film and glass. The influence of adding oil, as a friction modifier, on the surface properties of the substrate and the structure of the resultant filaments was evaluated. Wettability of each substrate in the absence of oil, and the presence of a thin layer and a thick layer of oil was studied. Circularity of the filaments was measured using image analysis of the cross sections and was correlated with the surface properties of the substrates. It was found that while the surface properties of the collection substrate were related to the uniformity and cross section circularity of the filaments, those spun on a thick layer of oil had the best circular shape irrespective of the substrate material. The results of this study can be used to optimize dry-spinning of CNF filaments.