Nanocelluloses (NC) are nature-based sustainable biomaterials, which not only possess cellulosic properties but also have the important hallmarks of nanomaterials, such as large surface area, ...versatile reactive sites or functionalities, and scaffolding stability to host inorganic nanoparticles. This class of nanomaterials offers new opportunities for a broad spectrum of applications for clean water production that were once thought impractical. This Review covers substantial discussions based on evaluative judgments of the recent literature and technical advancements in the fields of coagulation/flocculation, adsorption, photocatalysis, and membrane filtration for water decontamination through proper understanding of fundamental knowledge of NC, such as purity, crystallinity, surface chemistry and charge, suspension rheology, morphology, mechanical properties, and film stability. To supplement these, discussions on low-cost and scalable NC extraction, new characterizations including solution small-angle X-ray scattering evaluation, and structure–property relationships of NC are also reviewed. Identifying knowledge gaps and drawing perspectives could generate guidance to overcome uncertainties associated with the adaptation of NC-enabled water purification technologies. Furthermore, the topics of simultaneous removal of multipollutants disposal and proper handling of post/spent NC are discussed. We believe NC-enabled remediation nanomaterials can be integrated into a broad range of water treatments, greatly improving the cost-effectiveness and sustainability of water purification.
Cellulose is one of the most important natural polymers on earth and its various nanoscale forms provide new opportunities for groundbreaking discoveries in materials science. The current state of ...nanocellulose research and development, in terms of production and processing (including international market launch), structural details, properties, and innovative applications in life sciences and engineering technology is featured.
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Nanocelluloses are natural materials with at least one dimension in the nano-scale. They combine important cellulose properties with the features of nanomaterials and open new horizons for materials science and its applications. The field of nanocellulose materials is subdivided into three domains: biotechnologically produced bacterial nanocellulose hydrogels, mechanically delaminated cellulose nanofibers, and hydrolytically extracted cellulose nanocrystals. This review article describes today’s state regarding the production, structural details, physicochemical properties, and innovative applications of these nanocelluloses. Promising technical applications including gels/foams, thickeners/stabilizers as well as reinforcing agents have been proposed and research from last five years indicates new potential for groundbreaking innovations in the areas of cosmetic products, wound dressings, drug carriers, medical implants, tissue engineering, food and composites. The current state of worldwide commercialization and the challenge of reducing nanocellulose production costs are also discussed.
Bio-based nanocellulose has been shown to possess impressive mechanical properties and simplicity for chemical modifications. The chemical properties are largely influenced by the surface area and ...functionality of the nanoscale materials. However, finding the typical cross-sections of nanocellulose, such as cellulose nanofibers (CNFs), has been a long-standing puzzle, where subtle changes in extraction methods seem to yield different shapes and dimensions. Here, we extracted CNFs from wood with two different oxidation methods and variations in degree of oxidation and high-pressure homogenization. The cross-sections of CNFs were characterized by small-angle X-ray scattering and wide-angle X-ray diffraction in dispersed and freeze-dried states, respectively, where the results were analyzed by assuming that the cross-sectional distribution was quantized with an 18-chain elementary microfibril, the building block of the cell wall. We find that the results agree well with a pseudosquare unit having a size of about 2.4 nm regardless of sample, while the aggregate level strongly depends on the extraction conditions. Furthermore, we find that aggregates have a preferred cohesion of phase boundaries parallel to the (110)-plane of the cellulose fibril, leading to a ribbon shape on average.
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Unbleached wood fibers and nanofibers are environmentally friendly bio-based candidates for material production, in particular, as reinforcements in polymer matrix biocomposites due to their ...low density and potential as carbon sink during the materials production phase. However, producing high reinforcement content biocomposites with degradable or chemically recyclable matrices is troublesome. Here, we address this issue with a new concept for facile and scalable in-situ polymerization of polyester matrices based on functionally balanced oligomers in pre-formed lignocellulosic networks. The idea enabled us to create high reinforcement biocomposites with well-dispersed mechanically undamaged fibers or nanocellulose. These degradable biocomposites have much higher mechanical properties than analogs in the literature. Reinforcement geometry (fibers at 30 µm or fibrils at 10–1000 nm diameter) influenced the polymerization and degradation of the polyester matrix. Overall, this work opens up new pathways toward environmentally benign materials in the context of a circular bioeconomy.
The deformation micromechanics of bacterial cellulose (BC) and microfibrillated cellulose (MFC) networks have been investigated using Raman spectroscopy. The Raman spectra of both BC and MFC networks ...exhibit a band initially located at ∼1095 cm–1. We have used the intensity of this band as a function of rotation angle of the specimens to study the cellulose fibril orientation in BC and MFC networks. We have also used the change in this peak’s wavenumber position with applied tensile deformation to probe the stress-transfer behavior of these cellulosic materials. The intensity of this Raman band did not change significantly with rotation angle, indicating an in-plane 2D network of fibrils with uniform random orientation; conversely, a highly oriented flax fiber exhibited a marked change in intensity with rotation angle. Experimental data and theoretical analysis shows that the Raman band shift rate arising from deformation of networks under tension is dependent on the angles between the axis of fibrils, the strain axis, the incident laser polarization direction, and the back scattered polarization configurations. From this analysis, the effective moduli of single fibrils of BC and MFC in the networks were estimated to be in the ranges of 79–88 and 29–36 GPa, respectively. It is shown also that for the model to fit the data it is necessary to use a negative Poisson’s ratio for MFC networks and BC networks. Discussion of this in-plane “auxetic” behavior is given.
Unbleached lignocellulosic wood fiber materials of low porosity are of great interest as eco-friendly load-bearing materials because their yield is much higher than that for “pure” wood cellulosics. ...The difference between comparable materials based on lignocellulose fibers or nanocellulose is investigated. The structure, surface area, mechanical properties, moisture sorption, and optical properties of films based on fibers or microfibrillated lignocellulose (MFLC) were characterized as a function of lignin content, and the environmental impact was compared. The modulus and tensile strength of comparable fiber and MFLC films (≈25% porosity) increased up to an optimum lignin content (11–17%) and then decreased at a very high lignin content. Hot-pressed MFLC films with little porosity showed excellent properties, 230–260 MPa strength, 17–20 GPa modulus, and 81 MPa wet strength. The mechanical property values of hot-pressed wood fibers with 25% porosity were also as high as 154 MPa strength and 13.2 GPa modulus, which are higher than those of comparable materials reported in the literature. Because hot-pressed lignocellulose fibers can be readily recycled and show low cumulative energy demand, they are candidates for semistructural engineering materials. MFLC is of great interest for coatings, films, adhesives, and as additives or in high-technology applications.
Cellulose nanofibrils offer interesting potential as a native fibrous constituent of mechanical performance exceeding the plant fibers in current use for commercial products. In the present study, ...wood nanofibrils are used to prepare porous cellulose nanopaper of remarkably high toughness. Nanopapers of different porosities and from nanofibrils of different molar mass are prepared. Uniaxial tensile tests are performed and structure−property relationships are discussed. The high toughness of highly porous nanopaper is related to the nanofibrillar network structure and high mechanical nanofibril performance. Also, molar mass correlates with tensile strength. This indicates that nanofibril fracture controls ultimate strength. Furthermore, the large strain-to-failure means that mechanisms, such as interfibril slippage, also contributes to inelastic deformation in addition to deformation of the nanofibrils themselves.
It is demonstrated that it is possible to coat the individual fibers of wood-based nanocellulose with polypyrrole using in situ chemical polymerization to obtain an electrically conducting continuous ...high-surface-area composite. The experimental results indicate that the high surface area of the water dispersed material, to a large extent, is maintained upon normal drying without the use of any solvent exchange. Thus, the employed chemical polymerization of polypyrrole on the microfibrillated cellulose (MFC) nanofibers in the hydrogel gives rise to a composite, the structure of whichunlike that of uncoated MFC paperdoes not collapse upon drying. The dry composite has a surface area of ∼90 m2/g and a conductivity of ∼1.5 S/cm, is electrochemically active, and exhibits an ion-exchange capacity for chloride ions of 289 C/g corresponding to a specific capacity of 80 mAh/g. The straightforwardness of the fabrication of the present nanocellulose composites should significantly facilitate industrial manufacturing of highly porous, electroactive conductive paper materials for applications including ion-exchange and paper-based energy storage devices.
The layer-by-layer (LbL) deposition method was used for the build-up of alternating layers of nanofibrillated cellulose (NFC) or carboxymethyl cellulose (CMC) with a branched, cationic ...polyelectrolyte, polyethyleneimine (PEI) on flexible poly (lactic acid) (PLA) substrates. With this procedure, optically transparent nanocellulosic films with tunable gas barrier properties were formed. 50 layer pairs of PEI/NFC and PEI/CMC deposited on PLA have oxygen permeabilities of 0.34 and 0.71 cm3·μm/m2·day·kPa at 23 °C and 50% relative humidity, respectively, which is in the same range as polyvinyl alcohol and ethylene vinyl alcohol. The oxygen permeability of these multilayer nanocomposites outperforms those of pure NFC films prepared by solvent-casting. The nanocellulosic LbL assemblies on PLA substrates was in detailed characterized using a quartz crystal microbalance with dissipation (QCM-D). Atomic force microscopy (AFM) reveals large structural differences between the PEI/NFC and the PEI/CMC assemblies, with the PEI/NFC assembly showing a highly entangled network of nanofibrils, whereas the PEI/CMC surfaces lacked structural features. Scanning electron microscopy images showed a nearly perfect uniformity of the nanocellulosic coatings on PLA, and light transmittance results revealed remarkable transparency of the LbL-coated PLA films. The present work demonstrates the first ever LbL films based on high aspect ratio, water-dispersible nanofibrillated cellulose, and water-soluble carboxymethyl cellulose polymers that can be used as multifunctional films and coatings with tailorable properties, such as gas barriers and transparency. Owing to its flexibility, transparency and high-performance gas barrier properties, these thin film assemblies are promising candidates for several large-scale applications, including flexible electronics and renewable packaging.
The possibility of forming self-organized films using only charge-stabilized dispersions of cellulose I nanofibrils with opposite charges is presented, that is, the multilayers were composed solely ...of anionically and cationically modified microfibrillated cellulose (MFC) with a low degree of substitution. The build-up behavior and the properties of the layer-by-layer (LbL)-constructed films were studied using a quartz crystal microbalance with dissipation (QCM-D) and stagnation point adsorption reflectometry (SPAR). The adsorption behavior of cationic/anionic MFC was compared with that of polyethyleneimine (PEI)/anionic MFC. The water contents of five bilayers of cationic/anionic MFC and PEI/anionic MFC were approximately 70 and 50%, respectively. The MFC surface coverage was studied by atomic force microscopy (AFM) measurements, which clearly showed a more dense fibrillar structure in the five bilayer PEI/anionic MFC than in the five bilayer cationic/anionic MFC. The forces between the cellulose-based multilayers were examined using the AFM colloidal probe technique. The forces on approach were characterized by a combination of electrostatic and steric repulsion. The wet adhesive forces were very long-range and were characterized by multiple adhesive events. Surfaces covered by PEI/anionic MFC multilayers required more energy to be separated than surfaces covered by cationic/anionic MFC multilayers.
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