Cellulose: A Review of Water Interactions, Applications in Composites, and Water Treatment.

Cellulose is known to interact well with water, but is insoluble in it. Many polysaccharides such as cellulose are known to have significant hydrogen bond networks joining the molecular chains, and yet they are recalcitrant to aqueous solvents. This review charts the interaction of cellulose with water but with emphasis on the formation of both natural and synthetic fiber composites. Covering studies concerning the interaction of water with wood, the biosynthesis of cellulose in the cell wall, to its dispersion in aqueous suspensions and ultimately in water filtration and fiber-based composite materials this review explores water-cellulose interactions and how they can be exploited for synthetic and natural composites. The suggestion that cellulose is amphiphilic is critically reviewed, with relevance to its processing. Building on this, progress made in using various charged and modified forms of nanocellulose to stabilize oil-water emulsions is addressed. The role of water in the aqueous formation of chiral nematic liquid crystals, and subsequently when dried into composite films is covered. The review will also address the use of cellulose as an aid to water filtration as one area where interactions can be used effectively to prosper human life.

Self-Healing Composite Coating Fabricated with a Cystamine Cross-Linked Cellulose Nanocrystal-Stabilized Pickering Emulsion.

A gelled Pickering emulsion system was fabricated by first stabilizing linseed oil droplets in water with dialdehyde cellulose nanocrystals (DACNCs) and then cross-linking with cystamine. Cross-linking of the DACNCs was shown to occur by a reaction between the amine groups on cystamine and the aldehyde groups on the CNCs, causing gelation of the nanocellulose suspension. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the cystamine-cross-linked CNCs (cysCNCs), demonstrating their presence. Transmission electron microscopy images evidenced that cross-linking between cysCNCs took place. This cross-linking was utilized in a linseed oil-in-water Pickering emulsion system, creating a novel gelled Pickering emulsion system. The rheological properties of both DACNC suspensions and nanocellulose-stabilized Pickering emulsions were monitored during the cross-linking reaction. Dynamic light scattering and confocal laser scanning microscopy (CLSM) of the Pickering emulsion before gelling imaged CNC-stabilized oil droplets along with isolated CNC rods and CNC clusters, which had not been adsorbed to the oil droplet surfaces. Atomic force microscopy imaging of the air-dried gelled Pickering emulsion also demonstrated the presence of free CNCs alongside the oil droplets and the cross-linked CNC network directly at the oil-water interface on the oil droplet surfaces. Finally, these gelled Pickering emulsions were mixed with poly(vinyl alcohol) solutions and fabricated into self-healing composite coating systems. These self-healing composite coatings were then scratched and viewed under both an optical microscope and a scanning electron microscope before and after self-healing. The linseed oil was demonstrated to leak into the scratches, healing the gap automatically and giving a practical approach for a variety of potential applications.

Tackling the challenge of drying and redispersion of cellulose nanofibrils via membrane-facilitated liquid phase exchange.

It is generally acknowledged that to advance the application of cellulose nanofibrils (CNFs) in product formulations, challenges associated with the drying and redispersion of this material must be addressed. Despite increased research efforts in this area, these interventions still involve the use of additives or conventional drying technologies, which both have the capacity to drive up the cost of the final CNF powders. Herein, we prepared dried and redispersible CNF powders with varying surface functionalities without the use of additives nor conventional drying technologies. Rapid drying in air was achieved after liquid phase exchange from water to isopropyl alcohol. The surface properties, morphology and thermal stabilities were the same for the never-dried and redispersed forms. The rheological properties of the CNFs were also unaffected after drying and redispersion of unmodified and organic acid modified materials. However, for 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-mediated oxidised CNFs with higher surface charge and longer fibrils, the storage modulus could not be recovered to the never-dried state because of the possible non-selective reduction in length upon redispersion. Nevertheless, this method provides an effective and low-cost process for the drying and redispersion of unmodified and surface modified CNFs.

Amphiphilic Cellulose Nanocrystals for Aqueous Processing of Thermoplastics.

Conventional composite formulation of cellulose nanocrystals (CNCs) with thermoplastics involves melt compounding or in situ polymerisation. In this rather unconventional approach, polypropylene (PP) microparticles were finely suspended and stabilized, at varying weight loadings, in aqueous suspensions of amphiphilic CNCs to enable adsorption of the nanoparticles onto the thermoplastic. In order to achieve these suspensions, CNCs were modified with either octyl or hexadecyl groups. These modifications imparted hydrophobic properties to the CNCs, hence increasing interfacial adhesion to the PP microparticles. The modification, however, also retained the sulfate half ester groups that ensured dispersibility in aqueous media. The CNCs were evidently coated on the PP microparticles as revealed by confocal microscope imaging and had no detrimental effect on the melt properties of the PP-based composites. The approach is demonstrated to increase the Young's moduli of CNC-thermoplastic composites prepared in optimum suspension loadings of 0.5 wt. % octyl-modified and 0.1 wt % hexadecyl-modified CNCs. This procedure can be extended to other thermoplastics as the ability to aqueously process these composites is a major step forward in the drive for more sustainable manufacturing.

Stable Sodium-Metal Batteries in Carbonate Electrolytes Achieved by Bifunctional, Sustainable Separators with Tailored Alignment.

Sodium (Na) is the most appealing alternative to lithium as an anode material for cost-effective, high-energy-density energy-storage systems by virtue of its high theoretical capacity and abundance as a resource. However, the uncontrolled growth of Na dendrites and the limited cell cycle life impede the large-scale practical implementation of Na-metal batteries (SMBs) in commonly used and low-cost carbonate electrolytes. Herein, the employment of a novel bifunctional electrospun nanofibrous separator comprising well-ordered, uniaxially aligned arrays, and abundant sodiophilic functional groups is presented for SMBs. By tailoring the alignment degree, this unique separator integrates with the merits of serving as highly aligned ion-redistributors to self-orientate/homogenize the flux of Na-ions from a chemical molecule level and physically suppressing Na dendrite puncture at a mechanical structure level. Remarkably, unprecedented long-term cycling performances at high current densities (≥1000 h at 1 and 3 mA cm-2 , ≥700 h at 5 mA cm-2 ) of symmetric cells are achieved in additive-free carbonate electrolytes. Moreover, the corresponding sodium-organic battery demonstrates a high energy density and prolonged cyclability over 1000 cycles. This work opens up a new and facile avenue for the development of stable, low-cost, and safe-credible SMBs, which could be readily extended to other alkali-metal batteries.

The effects of morpholine pre-treated and carboxymethylated cellulose nanofibrils on the properties of alginate-based hydrogels.

The effects of varying percentage loadings of morpholine pre-treated cellulose nanofibrils (MCNF) and carboxymethylated cellulose nanofibrils (CMCNF) on the aqueous swelling, compressive modulus and viscoelastic properties of calcium-ion-crosslinked alginate hydrogels were investigated. In addition, the pore structures of hydrogels with the highest compressive modulus were studied. The incorporation of 5 wt. % MCNF resulted in a slightly reduced aqueous swelling, a 36% increase in compressive modulus and a layered pore structure when compared with the neat alginate hydrogel. On the other hand, the addition of CMCNF at the same loading led to a slightly improved aqueous swelling, an increase in compressive modulus (17%) and high porosity. Further increases in CNF loadings did not result in significant increase in material properties. The alginate/CNF composite materials have potentials to be used in applications where good swelling and mechanical robustness are required.