Drying cellulose nanofibrils: in search of a suitable method

Abstract

Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufacturing approaches. Cellulose nanofibrils (CNFs) are typically processed as aqueous suspensions because of their hydrophilic nature. One of the major manufacturing challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD). The particle size and morphology of the CNFs were determined via dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and morphological analysis. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were observed in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a technically suitable manufacturing process to dry CNF suspensions.

Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer

“…Preparation of dry microfibrillated cellulose powder without hornification could be of great interest in industrial application. Freeze-drying represents a potential option, because it largely preserves the fibrillary structure of MFC without agglomeration during the drying process (Peng et al 2012). Nanocellulose powder was prepared by combining freezing drying and surfactant treatment, and it was re-dispersed in PLA-chloroform solution to prepare PLA composites (Petersson et al 2007).…”

“…Nanocellulose powder was prepared by combining freezing drying and surfactant treatment, and it was re-dispersed in PLA-chloroform solution to prepare PLA composites (Petersson et al 2007). Drying in supercritical CO2 is also a good way to produce dry NFC, as it keeps the dimensions in nano size (Peng et al 2012). However, both of these two methods are of high cost and impractical to scale up.…”

Electroosmotic dewatering of cellulose nanocrystals

“…Á vila Ramírez et al 2017;Bai et al 2009;Cranston and Gray 2006;Kedzior et al 2016). Many industrial applications require that this solid content is increased and different drying methods, such as thermal, freeze and supercritical drying, can be used to obtain a dry material (Peng et al 2012(Peng et al , 2013. However, these techniques are associated with significant energy demands.…”

Surface properties and porosity of highly porous, nanostructured cellulose II particles

“…This freeze-drying method was also used to obtain aerogels with surface areas of 284-349 m 2 /g starting from cellulose nanofibrils (CNF) (Sehaqui et al 2011;Saito et al 2011;Nemoto et al 2015). Apart from freeze-drying, cellulose suspensions can be as well dried by airdrying or spray-drying (Peng et al 2012;Rämänen et al 2012;Ganesan et al 2016). These methods yield xerogels which differ quite drastically from the aerogels reported here: they are denser and have smaller surface areas because of shrinkage and resulting particle agglomeration in the drying process (Aegerter et al 2011).…”