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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.

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... However, due to its strong hydrogen bonding, CNF is easily agglomerated into microscale in the drying state, and the redispersion of CNF into nanoscale is very challenging, even in water [3]. The dried form of CNF is particularly significant when performing thermoplastic processing, such as injection molding and extrusion, especially when conducting thermal melting process with non-polar material since water can be disadvantageous for the process [4]. Furthermore, in terms of the techno economy, dried CNF can significantly cut the cost of transportation and storage [5]. ...
... Removing water from CNF suspensions while maintaining nanoscale dimensions of the nanofibrils is complicated [4]. There are several methods for drying CNF suspension, including spray drying, freeze-drying, and oven drying. ...
... In the early days, the aerogel was produced by dissolving cellulose with suitable chemical compounds followed by precipitation and supercritical drying or freeze-drying to maintain the porous structure and prevent them from collapse [8]. However, when CNF suspension exposes a constant drying rate in oven drying, the suspension volume will reduce and experience shrinkage as water vaporize [4]. ...
Article
One major manufacturing challenge in nanocellulose production is getting the dry form of nanocellulose while maintaining its nano-size dimensions. Different drying techniques will produce nanocellulose with different sizes and morphologies. Each has its own specific application. This study performed three methods to dry nanocellulose suspension, specifically cellulose nanofiber, including freeze-drying, spray-drying, and oven drying. The morphology and particle size of the dried CNF were analyzed using Field Emission Scanning Electron Microscope (FE SEM). Sponge-like material, also known as aerogel with low density (0.01 – 0.02 g/cm ³ ) and high porosity (98%), was obtained via freeze-drying. Meanwhile, finely grounded solidly in a spherical and irregular form has resulted from the spray drying process of CNF, with an average diameter of less than 2 μm. Oven-dried CNF formed rigid thin film with a rough surface. However, the FE-SEM micrograph indicated that the nanoscale dimension of the oven-dried CNF has no longer existed. Therefore, oven-drying is not suggested as a drying method for nanocellulose.
... Nanofibrillated cellulose (NFC) hydrogel is a natural biomaterial, whose biocompatibility, noninvasive properties, and hydrophilicity have aroused interest in many research sites, such as in 3D cell culturing and biomedical applications. 1,2 Furthermore, the optimization of the drying of NFC hydrogel into a highly porous aerogel has been a subject of research 3,4 to be utilized in various chemical applications as well as in pharmaceutical ones. However, the tendency of the hydrophilic fibrils of the nanocellulose to form irreversible hydrogen bonds between each other and aggregate during the drying process have created obstacles in the drying trials of NFC 5 and prevents the reconstitution back to hydrogel. ...
... Different drying methods for NFC hydrogel have been applied to obtain aerogel with an intact nanoscale structure and 3D network. 3,4 In addition, subsequent reconstitution of the FD TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl)oxyl]-oxidized NFC (ANFC) hydrogel has been studied, where the surface charge density of the NFC fibrils has decreased the aggregation of the structure and this way has facilitated the freeze-drying process when compared to native one. 13 However, with the comprehensive optimization of the freeze-drying process and by finding the optimal quantity of the biomolecules, we have shown now, for the first time, that the properties of the native NFC hydrogel after the freeze-drying and reconstitution can be preserved without further chemical modifications. ...
... Both FD NFC hydrogel formulations formed organized porous structure evidenced by the SEM images, which could be explained by the formation of ice crystals during freeze-drying. 4 Moreover, obtained PXCT images showed the FD NFC hydrogel formulation including sucrose to be homogeneous by having evenly formed 3D structure as well as the electron density in the narrow range throughout the whole sample. The homogeneous structure and organized porosity of the aerogel with the presence of sucrose might be valuable parameters to follow when considering the reconstitution back to the hydrogel. ...
Article
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The diversity and safety of nanofibrillated cellulose (NFC) hydrogels have gained a vast amount of interest at the pharmaceutical site in recent years. Moreover, this biomaterial has a high potential to be utilized as a protective matrix during the freeze-drying of heat-sensitive pharmaceuticals and biologics to increase their properties for long-term storing at room temperature and transportation. Since freeze-drying and subsequent reconstitution have not been optimized for this biomaterial, we must find a wider understanding of the process itself as well as the molecular level interactions between the NFC hydrogel and the most suitable lyoprotectants. Herein we optimized the reconstitution of the freeze-dried NFC hydrogel by considering critical quality attributes required to ensure the success of the process and gained insights of the obtained experimental data by simulating the effects of the used lyoprotectants on water and NFC. We discovered the correlation between the measured characteristics and molecular dynamics simulations and obtained successful freeze-drying and subsequent reconstitution of NFC hydrogel with the presence of 300 mM of sucrose. These findings demonstrated the possibility of using the simulations together with the experimental measurements to obtain a more comprehensive way to design a successful freeze-drying process, which could be utilized in future pharmaceutical applications.
... Thereinto, liquid storage strategy needs large storage volume and increased the transportation cost, while dry storage can considerably reduce its volume, making it more stable and reducing transportation and storage costs. However, it can also lead to the irreversible aggregation of cellulose fibrils caused by intermolecular bonding due to increasing the proximity of cellulose chains during the dehydration, resulting the limitation of large-scale application Peng et al. 2011). Over the last few years, many continuous efforts have been devoted to solving these problems. ...
... There have been some studies on the drying condition of CNFs, such as drying method, drying cycles and drying temperature, however, the drying technologies for LCNFs still deserves investigation on structural changes of cellulose caused by drying conditions (Huang et al. 2020;Kwak et al. 2019;Mo et al. 2020;Peng et al. 2011). Therefore, an effective way of the full use of common drying methods including ovendrying, spray-drying, freeze-drying, supercritical drying, evaporation and vacuum drying should be considered to solve the reduction of properties of aggregated nanofibrils (Ding et al. 2018;Hanif et al. 2017;Jiang and Hsieh, 2014;Kwak et al. 2019;Silva et al. 2021;Wang et al. 2019). ...
... Oven-drying (OD) was conducted by the evaporation of water molecule, and the strong intermolecular hydrogen bonds developed to form a continuous fiber network and a relatively solid bulk material under the effect of capillary and diffusion forces in the process of the evaporation of water molecule (Peng et al. 2011). The mechanism of centrifugal followed by vacuum drying (CVD) and evaporation followed by vacuum drying (EVD) was extended from the basis of OD. ...
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Having the advantages of a higher yield, lower cost and less environmental impact, lignin-containing cellulose nanofibrils (LCNFs) obtained by mechanically fibrillating unbleached pulps have been demonstrated to be a promising alternative to high-purity nanocellulose. In this study, the structural changes after four drying methods containing freeze-drying (FD), oven-drying (OD), centrifugal followed by vacuum-drying (CVD), and evaporation followed by vacuum-drying (EVD), and efficient reuse of LCNFs were extensively explored. It was found that the structural characteristics of LCNFs after drying were maintained by freeze drying with high lignin contents where the aggregation of fibrils was alleviated by lignin. The freeze-dried LCNFs were further redispersed by homogenizer in water, which exhibited excellent dispersion characteristics. In addition, the redispersed LCNFs were further assembled into PVA films to fabricate high-strength composites. The results showed that when the addition of redispersed LCNFs was up to 16.9%, the tensile strength and elongation at break of the as-prepared composite film increased by 325.2% and 335.2%, respectively. This study demonstrated a more sustainable approach to utilize LCNFs to produce biomass-based composite films than those of CNF-based composite films. Graphical abstract
... When cellulose is dried from air it will form large, micrometer-sized aggregates (Peng et al. 2012). Such drying-induced association is a technical problem of great significance since the dry fibrils can be difficult to redisperse. ...
... This has large consequences for the industrial use of nanocellulose since fibrils have to be kept in their dispersed state, with large transportation costs as a consequence (Posada et al. 2020). The extent of hornification depends strongly on drying methods (Peng et al. 2012;Nodenström 2020) and can also be mitigated by additives such as glycerol (Moser et al. 2018), which presumably act as spacers between fibrils. It also depends on surface chemistry of the fibrils (Benselfelt et al. 2019), where for instance acetylation was shown to reduce the work of adhesion between fibrils in water due to the surface acetyl groups preventing tight association leading to the interpenetration of water molecules at the interface (Fig. 6). ...
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In the cellulose scientific community, hydrogen bonding is often used as the explanation for a large variety of phenomena and properties related to cellulose and cellulose based materials. Yet, hydrogen bonding is just one of several molecular interactions and furthermore is both relatively weak and sensitive to the environment. In this review we present a comprehensive examination of the scientific literature in the area, with focus on theory and molecular simulation, and conclude that the relative importance of hydrogen bonding has been, and still is, frequently exaggerated.
... and C-CNCs. Moreover, abundant white spots and big fibers can be observed on the surface of the CNFs, thought to have formed because of the aggregation of the CNFs via hydrogen bonds and van der Waals forces, which might have occurred during their drying (Peng et al. 2012;Niu et al. 2018). During the drying of the CNFs, the forces resulting from the removal of water at high temperature may drive the molecular contact that facilitates the occurrence of the above forces (Peng et al. 2012). ...
... Moreover, abundant white spots and big fibers can be observed on the surface of the CNFs, thought to have formed because of the aggregation of the CNFs via hydrogen bonds and van der Waals forces, which might have occurred during their drying (Peng et al. 2012;Niu et al. 2018). During the drying of the CNFs, the forces resulting from the removal of water at high temperature may drive the molecular contact that facilitates the occurrence of the above forces (Peng et al. 2012). Another possibility is that these aggregates may have already formed in the dispersion even before the drying process because CNFs were not completely separated. ...
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When applying an adhesive to wood, the chemical heterogeneity of the wood cell walls makes it difficult to understand the contribution they make to the interfacial adhesion between the adhesive and the wood as the adhesion is a very complex physical and chemical phenomenon. This study, for the first time, directly measured the surface adhesion between cellulose, a major component of wood, and urea–formaldehyde (UF) resin adhesives. The adhesion between thin, smooth nanocellulose films, such as cellulose nanofibrils (CNFs), carboxymethylated nanofibrils (CM)–CNFs, and carboxylated cellulose nanocrystals (C–CNCs), and UF resins with two formaldehyde to urea (F/U) molar ratios of 1.0 and 1.6 was measured using two approaches: (1) direct measurement of the adhesion force between nanocellulose films and liquid droplets of the UF resins, and (2) calculation of the work of adhesion between films of the nanocelluloses and UF resins using the contact angle and the van Oss–Chaudhury–Good method. The results show that the total surface free energies, either between the different nanocelluloses or between the two UF resins are somewhat similar, indicating the similarity in their surface properties. However, the adhesion force and work of adhesion of 1.6 UF resins with different types of nanocellulose are higher than those of 1.0 UF resins, which shows that van der Waals forces are dominant in their molecular interactions. These results suggest that the adhesion between 1.6 UF resins and nanocellulose is stronger than that when 1.0 UF resins are used because the 1.6 UF resins have a more branched structure, smoother surface, and higher surface free energy. Graphic abstract
... More commonly, colloidal NCC dispersions at 2-10% w/v can be prepared (Börjesson & Westman, 2015). Sometimes, drying may be carried out to minimize bulkiness and transportation costs but the redispersibility of completely dried NCCs can be challenging (Peng, Gardner, & Han, 2012). Various drying methods such as air drying, oven drying, supercritical drying, freeze-drying and spray drying have been studied but spray drying may be more practical for scale-up (Han, Zhou, Wu, Liu, & Wu, 2013;Peng et al., 2012;Voronova, Zakharov, Kuznetsov, & Surov, 2012). ...
... Sometimes, drying may be carried out to minimize bulkiness and transportation costs but the redispersibility of completely dried NCCs can be challenging (Peng, Gardner, & Han, 2012). Various drying methods such as air drying, oven drying, supercritical drying, freeze-drying and spray drying have been studied but spray drying may be more practical for scale-up (Han, Zhou, Wu, Liu, & Wu, 2013;Peng et al., 2012;Voronova, Zakharov, Kuznetsov, & Surov, 2012). Neutralization of NCCs with sodium hydroxide before drying can easily improve the redispersibility into suspensions (Beck et al., 2012). ...
Article
The use of nanocrystalline cellulose (NCC) as a renewable and green biomaterial in diverse value-added applications has roused substantial interest. Sourcing NCCs from the abundantly available non-woody biomass becomes attractive due to its high cellulose content and low cost. Acid hydrolysis using mineral acids has been widely explored as a facile, low-cost, and efficient way of isolating NCCs. Still, the technical aspect of the extraction procedure is lacking. This review gathers the available knowledge on the NCC extraction using hydrolysis with mineral acids from non-woody biomass and provides a critical overview of the extraction parameters to be considered from the feedstocks and related pretreatment to the final hydrolysis procedure. To fulfill an operationally feasible production of NCCs, this review shares considerations and challenges on the biomass characteristics and pretreatment as well as hydrolysis parameters for optimizing NCC production and tailoring its application.
... The small pores in the eluted IGCPA collapsed to form large pores, which caused the S BET of the aerogel to become larger and the pore size also increased. In addition, the specific surface area of composite aerogels was generally smaller, most likely due to the formation of large aggregates or aggregates during drying (Peng et al., 2011;Brinkmann et al., 2016;Zheng et al., 2020). ...
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Because of dysprosium’s unique physical and chemical properties and limited supply, the price of rare earth dysprosium has been high in recent years. Therefore, the study of the method of high efficiency selective separation of dysprosium has the double value of scientific research and practical economy. In this paper, we used periodic cellulose nanocrystals as the basic structure, polyethylenimine and graphene oxide were introduced, combined with imprinting technology, to construct a porous imprinted aerogel and use it for selective adsorption of Dy(III). The physical and chemical properties were characterized by SEM, FT-IR and TGA. It was proved that both polyethylenimine and graphene oxide were crosslinked effectively with cellulose nanocrystals. Adsorption experiments showed that the composite imprinted aerogel could selectively adsorb dysprosium effectively, and the maximum adsorption capacity for Dy(III) was 36.495 mg g−1. The reproducibility experiment showed that aerogel had good regeneration ability. In conclusion, cellulose nanocrystal aerogel, which is environmentally friendly, efficient and repeatable, is expected to provide a new direction for the recovery of rare earth elements.
... Transferring material concepts designed for printing into papermaking conditions is not, however, that straightforward. Using nanocelluloses as the web-forming material alone is simply not possible due to its small size and water retention capacity (Peng et al 2012), why exchanging the nanoscale cellulose fibrils into macroscale pulp fibers would make the transition easier. The forming section in papermaking, where the fiber suspension is drained over a coarse wire, further put demands on a well-designed system in order to retain the materials to be included in the web. ...
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The global electrification of our society requires an enormous capacity of electrical energy storage. This drives the demand for low-cost and sustainable solutions, where the electrode materials are key components. In the present work, all-organic supercapacitor electrodes have successfully been demonstrated to be produced on a pilot-scale paper machine, thereby showing the feasibility of large-scale production of “paper-based energy storage”. The material concept was based on activated charcoal from pyrolyzed coconut and cationized cellulose pulp, the latter having small amounts of electrostatically adsorbed PEDOT:PSS in order to create a conducting, percolating network. In a pre-trial lab experiment, it was evident that even small addition of 1 wt% PEDOT:PSS gave a large increase in capacitance compared to samples with only activated charcoal. In the pilot trials, the addition of carboxymethylated nanocellulose and/or carbon black was further investigated. The different additions significantly affected several paper properties such as tensile strength and conductivity, but the specific capacitance of the activated charcoal was not affected and was found to be around 65-70 F/g. As more than half of the electrodes mass consisted of pulp fibers, the specific capacitance of the paper electrodes was about 25-30 F/g, which is in the same order of commercial supercapacitor electrodes. The successful production of several 10-meter-long rolls of supercapacitor electrode paper shows the feasibility of producing energy storage devices with papermaking methods, and the work as a whole provides valuable insights on how to further advance bio-based energy storage solutions.
... This structure was not apparent on the wood-mycelium particle surfaces ( Figure 6.2D). Under TEM, CNF appeared as thin elongated and branched fibers with multiple ramifications and sub-ramifications, which would easily form networks upon drying ( Figure 6.2D) (Diop et al., 2017;Peng et al., 2012). The thermal degradation profiles of raw materials reveal that most of the degradation occurred between 200 and 350 °C (Figure 6.3). ...
Article
The increasing environmental awareness has led to an increased interest in developing more sustainable materials as alternatives to petroleum-derived products. Among different nature-based products, fungal-mycelium-based bio-composites have gained considerable attention in various applications. Multiple materials with different densities and structures and potential applications can be fabricated by inoculating filamentous white-rot fungi in lignocellulosic materials and other substrates. Different from lower-density as-grown foam-like mycelium composites, higher-density mycelium-lignocellulosic panels have the potential to replace commercial particleboard and fiberboard bonded by petroleum-based resins. This kind of composite can be produced by directly adding heat and pressure to the low-density foams or by assembling mycelium-industry wastes before hot-pressing. The main goal of this dissertation was to investigate the principal adhesion mechanisms involved in the production of hot-pressed mycelium bio-composites. The functionality of surface mycelium for wood bonding was thoroughly investigated by growing Trametes versicolor on yellow birch veneers. The presence of surface mycelium improved the interface between two wood layers and consequently enhanced bonding. The surface mycelium layer was also confirmed to be able to be utilized as a stand-alone adhesive to bond untreated wood. The exopolysaccharides and proteins located at the interface between aerial mycelium and the substrate were confirmed to play an essential role in adhesion. The bonding mechanism and functionality of mycelium were also investigated in both as-grown and hot-pressed bio-composite structures. For low-density as-grown foam structures, fungal mycelium only worked as a binder, the lignocellulosic substrate material played an essential role in sound absorption and thermal insulation properties, and the denser mycelium structure had a negative effect on these properties. In a higher-density hot-pressed panel system, fungal mycelium contributed to bonding and reinforced the bio-composite by filling the gaps. Additionally, we also demonstrated that combining the advantages of nanocellulose research at UMaine into our novel mycelium bio-composite can provide further improvements in properties to manufacture formaldehyde-free hybrid composite panels. Finally, we discovered an all-natural mycelium surface with tunable wettability that can be switched several times from hydrophobic to hydrophilic status by a simple treatment. These surfaces can have potential applications in medical microfluidics and invisible pattern printing.
... Other techniques such as freeze-drying and supercritical CO 2 drying can produce a better nanoscale morphology but are currently costly and typically have a low throughput. 41,43 As seen in Figure 2, both BSK-and OCC-derived CNF agglomerate and form particles after spray drying. As these particles consist of agglomerated nanofibrils, they are referred to as "BSK-CNF" and "OCC-CNF" throughout the remainder of this article for consistency. ...
Article
Cellulose nanomaterials have attracted a great deal of interest as sustainable alternatives to nonrenewable or fossil fuel-derived materials, particularly in composite applications. Cellulose nanofibrils (CNF) are most often derived from wood sources through energy-intensive and costly mechanical fibrillation processes. In this study, recycled cardboard, referred to as old corrugated cardboard (OCC), was investigated as an alternate CNF source. OCC is a recycled material that can be obtained at one-tenth the cost of the commonly used bleached softwood Kraft pulp and can be refined to similar levels with nearly one-half of the energy consumption. Additionally, the distinct composition and morphology of OCC-derived CNF provides a more favorable fiber-matrix interface and better reinforcement capabilities of the cellulose nanofibrils in polymer matrices, displaying an over 70% increase in tensile modulus at a loading of 40 wt % with no decrease in tensile strength. When paired with biobased poly(l-lactide) (PLLA), OCC-derived CNF is proven to be an attractive low-cost and low-energy reinforcing agent for sustainable, high performance nanocomposites.
... On the contrary, CNCs are short rod-like materials with low or no entanglement, especially for ordered CNCs films, which cause the brittleness of the films and easy to crack with large dimension (Chowdhury et al., 2019). However, due to the much smaller size of CNC, the surface of CNC films are much smoother than those of CNF films (Peng et al., 2012(Peng et al., , 2013. CNC also has higher crystallinity, enabling CNC reinforced composites are more efficient on property improvement in terms of gas barrier performance. ...
Article
Nanocellulose based gas barrier materials have become an increasingly important subject, since it is a widespread environmentally friendly natural polymer. Previous studies have shown that super-high gas barrier can be achieved with pure and hierarchical nanocellulose films fabricated through simple suspension or layer-by-layer technique either by itself or incorporating with other polymers or nanoparticles. Improved gas barrier properties were observed for nanocellulose-reinforced composites, where nanocellulose partially impermeable nanoparticles decreased gas permeability effectively. However, for nanocellulose-based materials, the higher gas barrier performance is jeopardized by water absorption and shape deformation under high humidity conditions which is a challenge for maintaining properties in material applications. Thus, numerous investigations have been done to solve the problem of water absorption in nanocellulose-based materials. In this literature review, gas barrier properties of pure, layer-by-layer and composite nanocellulose films are investigated. The possible theoretical gas barrier mechanisms are described, and the prospects for nanocellulose-based materials are discussed.
... XRD spectrum of AEAN was studied by Bruker Advance D8 X-ray diffractometer (copper radiation (Kα); Germany) at 40 kV and 40 mA. The crystallite size was calculated by Scherrer's equation (Peng et al. 2012;Singh et al. 2017): where D hkl is the crystallite size, θ is the diffraction angle, λ is 1.5406 Å, and β is the full-width at halfmaximum (FWHM). ...
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Smart nanofibers have been used to create sensing tools for various purposes, such as anticounterfeiting. However, electrospinning produces nanofibers at a low yield, high cost, and requires high voltage. The recently invested solution blowing spinning method generates nanofibers at low cost and high yield without the need for high voltage. Moreover, the efficiency of nanofibrous coatings has been enhanced and strengthened by cellulose nanowhiskers (CNWs). Fluorescent photochromism is an interesting technique for the preparation of dual-mode security encoding authentication materials. Herein, novel photochromic emissive nanofibrous films composed of CNW-supported polyacrylonitrile (PAN) nanocomposite incorporated with alkaline earth activated aluminate nanoparticles (AEAN) was prepared to present security authentication films with optical photo-responsiveness for anticounterfeiting applications. To create a colorless film, AEAN and CNW must be well-dispersed in the PAN-based composite. Nanofiber-coated paper sheets were analyzed by luminescence spectra to display a green emission at 527 nm. The photochromic nanofiber-coated sheets demonstrated strong reversibility under UV and daylight. The current advance can be reported as an efficient strategy to manufacture authenticated merchandise.
... The removal of water is, however, challenging because of the large surface area of the material and its unique three-dimensional network structure in water that results in a gel-like structure. Methods currently suggested include thermal drying (e.g., spray drying), freeze drying, and super-critical drying, 17 all of which require an extensive amount of energy as the heat of evaporation of water is high at atmospheric pressure. Moreover, conventional drying techniques may lead to morphological changes (such as particle aggregation), commonly referred to as hornification. ...
Article
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An electroassisted filtration technique has been employed to improve dewatering of a suspension of microfibrillated cellulose (MFC) produced via 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. In addition, all-atom molecular dynamic (MD) simulations were performed to deepen the understanding of the complicated dewatering mechanism on a molecular level. Both the experimental and the simulation results implied that the dewatering rate was not only improved when electroassisted filtration was used but also found to be proportional to the strength of the electric field. A channeled dewatered structure was observed for these experiments and may have contributed to enhanced dewatering by providing high overall permeability. The MD simulations revealed that the electric field had a significant impact on the fibril movement, whereas the impact of pressure was limited. The simulations also suggested that the increased filtrate flow upon the application of an electric field was not only due to electroosmotic flow but also due to electrophoretic movement of the fibrils toward the anode that led to the release of water that had been trapped between the fibrils, allowing it to be pressed out together with the rest of the bulk water. This study shows that electroassisted filtration has the potential to improve the dewatering of TEMPO-MFC, and the MD simulations provide further insights into the dewatering mechanism.
... While the resolution of TEM can analyse bre width down to a few nanometres, SEM is only capable of analysing bre width greater than 100 nm (Kangas et al. 2014). In addition, the three-dimensional structure and bulk morphology of the sample is disrupted during the drying step required for sample preparation (Peng et al. 2012;Silva et al. 2021). Meanwhile, indirect characterisation involves measuring a derived property of the nano bre system, such as the bre-light interaction (DLS, UV-vis transmittance), bre-solvent interaction (rheology, sedimentation behaviour, water retention capacity), bre-bre interaction (nanopaper mechanical properties), or speci c surface area (SANS, SAXS, DSC, BET adsorption, solvent relaxation NMR, conductimetric titration). ...
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Characterising cellulose nanofibre (CNF) morphology has been identified as a grand challenge for the nanocellulose research field. Direct techniques for CNF morphology characterisation exhibit various difficulties related to the material network structure and equipment cost, while indirect techniques that investigate fibre-light interaction, fibre-solvent interaction, fibre-fibre interaction, or specific fibre surface area involve relatively facile methods but may be more unreliable. Nanopaper mechanical testing is a prevalent metric for assessing fibre-fibre interaction, but is an off-line, time-consuming, and destructive methodology. In this study, an optical fibre morphology analyser (MorFi, TechPap) was employed as an on-line, high throughput, fast turnaround tool to assess micro/nanofibre pulp morphology and predict the properties of nanopaper material. Correlation analysis identified fibre content and fibre kink properties as most correlated with nanopaper strength and toughness, while fibre width and coarseness were most inversely correlated with nanopaper performance. Principal component analysis (PCA) was employed to visualise interdependent morphological and mechanical data. Subsequently, two data driven statistical models - multiple linear regression (MLR) and machine learning based support vector regression (SVR) - were established to predict nanopaper properties from fibre morphology data, with SVR generating a more accurate prediction across all nanopaper properties (NRMSE = 0.13-0.33) compared to the MLR model (NRMSE = 0.33-0.51). This study highlights that statistical methods are useful to disentangle and visualise interdependent morphological data from an on-line fibre analysis device, while regression models are also capable of predicting paper mechanical properties from CNF samples even though these devices do not operate at nanoscale resolution.
... ZnCl 2 has an advantage for environmental loads and workers' health in the present and future industries in which green chemistry is required. In addition, the CNFs, and related fibrillation and drying technologies have been of importance to unthread vulcanized fibers (Saito et al. 2006;Isogai et al. 2011;Peng et al. 2012;Nemoto et al. 2015). With improved basics of CNFs and related analytical techniques, the classical aqueous ZnCl 2 treatment of cellulose has been reviewed from a new perspective (Nemoto et al. 2018;Burger et al. 2020). ...
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Vulcanized fibers are all-cellulose materials made from cotton and/or wood cellulose after aqueous zinc chloride treatment. These materials were invented in the UK in the mid-nineteenth century and is widely used because of their excellent characteristics, such as impact resistance and electrical insulation. Recently the matured vulcanized fibers have been recognized as renewable and biodegradable materials and reevaluated with advanced cellulose technologies derived from cellulose nanofibers (CNFs) and all-cellulose composites. The microscopic analysis based on the improved freeze-drying method revealed that the strength of vulcanized fiber sheets can be attributed to the chemically defibrillated CNFs. The architecture is similar to all-cellulose composites made from the same raw materials in which the residual cellulose fibers serve as reinforcement, and the CNFs serve as adhesives or matrix components. In this report, we describe the history and structural characteristics of vulcanized fibers and introduce a new aspect in aqueous zinc chloride treatment of cellulose. Graphical abstract
... After completion of the delignification process, subsequent air-drying of the isolated macrofibres creates a capillary tension that causes the constituent cellulose nanofibrils to collapse together 21 . The chemical delignification pretreatment and subsequent air-drying process is the key to achieving self-densification of the cellulose macrofibres. ...
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Synthetic fibres such as polyester and carbon are used in a broad variety of industries. However, as they derive from petrochemicals that are neither renewable nor biodegradable, the development of natural alternatives has gained increasing momentum in recent years. Here, we report a top-down approach for scalable production of cellulose macrofibres from bamboo stems involving a mild delignification process followed by water-assisted air-drying. Consisting of aligned and densely packed cellulose nanofibrils that possess strong hydrogen bonds and van der Walls forces, the extracted fibres exhibit a tensile strength of 1.90 ± 0.32 GPa, a Young’s modulus of 91.3 ± 29.7 GPa and a toughness of 25.4 ± 4.5 MJ m⁻³, which exceed those of wood-derived fibres and are comparable to synthetic carbon analogues. As a result of the low density, the specific strength is as high as 1.26 ± 0.21 GPa cm⁻³ g⁻¹, surpassing most reinforcing components such as steel wire, synthetic polymers and vitreous fibres. The life-cycle assessment reveals that replacing polymer and carbon fibres in structural composites with the current natural fibres leads to substantial reduction in carbon emissions. Our work suggests a pathway towards sustainability in wider areas of application, including automobiles, aeronautics and construction.
... While the resolution of TEM can analyse fibre width down to a few nanometres, SEM is only capable of analysing fibre width greater than 100 nm (Kangas et al. 2014). In addition, the three-dimensional structure and bulk morphology of the sample is disrupted during the drying step required for sample preparation (Peng et al. 2012;Silva et al. 2021). Meanwhile, indirect characterisation involves measuring a derived property of the nanofibre system, such as the fibre-light interaction (DLS, UV-vis transmittance), fibre-solvent interaction (rheology, sedimentation behaviour, water retention capacity), fibre-fibre interaction (nanopaper mechanical properties), or specific surface area (SANS, SAXS, DSC, BET adsorption, solvent relaxation NMR, conductimetric titration). ...
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Characterising cellulose nanofibre (CNF) morphology has been identified as a grand challenge for the nanocellulose research field. Direct techniques for CNF morphology characterisation exhibit various difficulties related to the material network structure and equipment cost, while indirect techniques that investigate fibre-light interaction, fibre-solvent interaction, fibre-fibre interaction, or specific fibre surface area involve relatively facile methods but may be more unreliable. Nanopaper mechanical testing is a prevalent metric for assessing fibre-fibre interaction, but is an off-line, time-consuming, and destructive methodology. In this study, an optical fibre morphology analyser (MorFi, Techpap) was employed as an on-line, high throughput, fast turnaround tool to assess micro/nanofibre pulp morphology and predict the properties of nanopaper material. Correlation analysis identified fibre content and fibre kink properties as most correlated with nanopaper strength and toughness, while fibre width and coarseness were most inversely correlated with nanopaper performance. Principal component analysis (PCA) was employed to visualise interdependent morphological and mechanical data. Subsequently, two data driven statistical models—multiple linear regression (MLR) and machine learning based support vector regression (SVR)—were established to predict nanopaper properties from fibre morphology data, with SVR generating a more accurate prediction across all nanopaper properties (NRMSE = 0.13–0.33) compared to the MLR model (NRMSE = 0.33–0.51). This study highlights that statistical methods are useful to disentangle and visualise interdependent morphological data from an on-line fibre analysis device, while regression models are also capable of predicting paper mechanical properties from CNF samples even though these devices do not operate at nanoscale resolution. Graphical abstract
... Redispersion of these dried particles into stable 50 suspensions that are comparable to that of the original particle dimensions is an ongoing challenge 51 due to the high energy requirements to break these hydrogen bonds (Beck et al. 2012;Missoum et 52 al. 2012;Beuguel et al. 2018). Traditional drying methods such as oven drying, spray drying, 53 freeze drying, suffer from loss of nanoscale dimension due to agglomeration of fibrils associated 54 with inter-particle hydrogen bonding (Peng et al. 2012a). Supercritical drying (Zimmermann et al. 55 2016) and solvent replacement drying (Hanif et al. 2018) are two methods that has been observed 56 to retain the nanoscale dimensions. ...
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Although cellulose nanomaterials have promising properties and performance in a wide application space, one hinderance to their wide scale industrial application has been associated with their economics of dewatering and drying and the ability to redisperse them back into suspension without introducing agglomerates or lose of yield. The present work investigates the dewatering of aqueous suspensions of cellulose nanofibrils (CNF) using ultrasound as a potentially low-cost, non-thermal, and scalable alternative to traditional heat-based drying methods such as spray drying. Specifically, we use vibrating mesh transducers to develop a direct-contact mode ultrasonic dewatering platform to remove water from CNF suspensions in a continuous manner. We demonstrate that the degree of dewatering is modulated by the number of transducers, their spatial configuration, and the flow rate of the CNF suspension. Water removal of up to 72 wt.% is achieved, corresponding to a final CNF concentration of 11 wt.% in 30 minutes using a twotransducer configuration. To evaluate the redispersibility of the dewatered CNF material, we use a microscopic analysis to quantify the morphology of the redispersed CNF suspension. By developing a custom software pipeline to automate image analysis, we compare the histograms of the dimensions (length, width) of the redispersed dewatered fibrils with the original CNF samples and observe no significant difference, suggesting that no agglomeration is induced due to ultrasonic dewatering. We estimate that this ultrasound dewatering technique is also energyefficient, consuming up to 36% less energy than the enthalpy of evaporation per kilogram of water. Together with the inexpensive cost of transducers (<$1), the potential for scaling up in parallel flow configurations, and excellent redispersion of the dewatered CNF, our work offers a proof-ofconcept of a sustainable CNF dewatering system, that addresses the shortcomings of existing techniques.
... According to the literature, freeze-dried nanocellulose samples should be easier to redisperse than samples dried by solvent evaporation with or without heat. 10,44,45 It is therefore herein suggested that the improved redispersibility of the nanopaper is a consequence of the structure of the dried material. During vacuum filtration, the CNFs first form an arrested state which collapses into a layered structure. ...
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The potential for large-scale applications of cellulose nanofibrils (CNFs) is limited by the high water content of the starting material, which leads to high transportation costs and undesirable environmental impact. However, drying of CNFs results in loss of their nanoscopic dimensions leading to deterioration of their unique inherent mechanical properties. Herein, thorough redispersion studies of both fundamental and applied nature have been conducted in order to evaluate the effect of charge, redispersing agent, and drying method. Freeze-dried CNF dispersions were successfully redispersed by either increasing the charge density or adding redispersing agents. The greatest effect on redispersibility was achieved with fractionated LignoBoost lignin as redispersing agent, and this is attributed to steric repulsion during water removal and reduced CNF adhesion. Furthermore, the results unexpectedly show that redispersion is easier when the CNFs are dried in the form of nanopapers. By using this approach, excellent redispersibility was achieved even without a redispersing agent. Nanopapers formed from the redispersed CNFs was found to have essentially the same mechanical properties as those made from never-dried CNFs. Hence, this work suggests solutions for making CNFs viable for large-scale application while maintaining their nanoscale dimensions and their ability to create nanopapers with excellent mechanical properties.
... In order to incorporate CNFs into composites through industrially viable processes, e.g., extrusion, water needs to be removed to prevent degradation of the polymer matrix, especially when used in biopolymers, and formation of porosity. A few strategies exist to dry CNF without the occurrence of hornification, but many, including freeze-drying and supercritical CO 2 drying, remain costly and difficult to use industrially (Peng et al. 2012;Sinquefield et al. 2020;Zimmermann et al. 2016). Additionally, CNFs, which are hydrophilic in nature, tend to aggregate when introduced into polymer matrices, as most are hydrophobic (Zhou et al. 2016). ...
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Cellulose nanofibrils (CNFs) have been widely used as a nanofiller for polymer composite reinforcement due to their excellent mechanical properties. However, CNF is produced in water and needs to be dried prior to use in composite materials. The presence of hydroxyl groups on the surface of CNF creates strong hydrogen bonding that makes it difficult and costly to dry. Additionally, the hydrophilicity at the fiber surface results in agglomeration of CNFs within many polymer matrices. In this study, chitosan (CS) was co-precipitated with CNF to produce a dual-bonding filler for use in poly (lactic acid) (PLA) composites. CS promotes improved interfacial interaction within the polymer matrix by forming strong hydrogen bonds with the CNF and potential covalent bonds with the PLA. The results confirmed that the addition of a small amount of CS significantly improved the mechanical properties compared to PLA + CNF composites and neat PLA. The detailed study of the PLA + CNF/CS composites reveals the synergetic effect of the hydrogen and covalent bonding mechanism for PLA reinforcement. Graphical abstract
... The input material that entered the compounding phase had to be prepared in a dried state; thus, the dispersions of unmodified and modified NFC were previously dried by the freeze-drying (lyophilisation) technique. A common phenomenon that occurs during the freeze-drying of the nanofibrillated cellulose dispersion is agglomeration, which was proved by Peng et al. [22]. The agglomerates also appeared in our dried samples of unmodified and modified NFC. ...
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Polylactic acid (PLA) is one of the most suitable materials for 3D printing. Blending with nanoparticles improves some of its properties, broadening its application possibilities. The article presents a study of composite PLA matrix filaments with added unmodified and lignin/polymerised lignin surface-modified nanofibrillated cellulose (NFC). The influence of untreated and surface-modified NFC on morphological, mechanical, technological, infrared spectroscopic, and dynamic mechanical properties was evaluated for different groups of samples. As determined by the stereo and scanning electron microscopy, the unmodified and surface-modified NFCs with lignin and polymerised lignin were present in the form of plate-shaped agglomerates. The addition of NFC slightly reduced the filaments’ tensile strength, stretchability, and ability to absorb energy, while in contrast, the initial modulus slightly improved. By adding NFC to the PLA matrix, the bending storage modulus (E’) decreased slightly at lower temperatures, especially in the PLA samples with 3 wt% and 5 wt% NFC. When NFC was modified with lignin and polymerised lignin, an increase in E’ was noticed, especially in the glassy state.
... Co., Ltd., Wenzhou, China. All the materials were used as received, while CNC was diluted with distilled water, followed by 10 min sonication and oven drying for 24 h in a beaker at 105°C (Peng et al., 2012). ...
Article
Carbon black (CB) and silica (Sil) as rubber reinforcement have raised environmental concerns for being high resources consumptive and less susceptible towards biodegradability. Cellulose nanocrystal (CNC) has demonstrated great potentials for use as biodegradable nanofillers in rubber nanocomposites while evaluation of its environmental impacts with optimal end-of-life (EOL) choices is not carried out. To simulate realistic EOL, thermo-oxidative aging and soil burial aging behaviors of rubber nanocomposites with 33.3% filler were performed. The environmental weathering performance modeled with the help of life cycle assessment (LCA) illustrates increased biodegradation susceptibility with partial replacement of CB or Sil with CNC in the nanocomposites, hence promoting the environmental solutions for waste minimalization by enhancing the biodegradability potentials. In terms of LCA, the CNC incorporation contributes more to the environmental impacts in manufacturing but greatly lowers the EOL choices, by reducing the global warming potential values.
... In addition, amorphous regions are separately split and particular crystallites are released with acidic treatment of cellulose [93,94]. CNC efficiency depends on many factors, including cellulose streams, hydrolysis acid forms, reaction time, and temperature [95]. Brinchi [96] stated that CNC's altered particle dimension, hydrophobicity, crystallinity, amorphous composition, and outer surface as well as molecular mass which is due to by various cellulose source and hydrolysis circumstances. ...
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Nanocellulose products derived from different forms of biomass have significant importance in the modern era. This is due to its extraordinary physical characteristics, wide surface area as well as its biodegradability, which lead to being promising reinforcements as a nanomaterial. The nanomaterials which represent the cellulosic structures comprise nanocellulose reinforcements with biodegradable characteristics and tremendous ability to be used in eco-friendly applications to supplant fossil-based products. Meanwhile, the syntheses approach of such nanoscale structures still possesses challenging tasks at nanoscales. In addition, the virtuous distribution of nanocellulose in the hydrophobic polymer matrix has still difficulties to produce high-performance nanomaterials. Consequently, this study concludes many approaches and techniques to structural alteration of cellulosic materials to improve the distribution of nanocellulose to enhance the characteristics and features of nanocomposites. The macroscale and nanoscale cellulosic structures get popularity because of their high strength, stiffness, biodegradability, renewability, and use in the preparation of nanocomposites. Application of cellulose nanofibres for the production of nanocomposites is a relatively recent research field. Cellulose macro- and nanofibres can be used as insulation nanocomposite materials because of the improved mechanical, thermal, and biodegradation properties of nanocomposites. Cellulose fibres are hydrophilic, so it became important to improve their surface roughness for the production of nanocomposites with improved properties. This article includes the surface modifications of cellulose fibres by different methods as well as production processes, properties, and various applications of nanocellulose and cellulosic nanocomposites. A high thermal conductivity of cellulosic nanocomposite material for electronic devices can be obtained by combining cellulose nanofibrils (CNF) as the framework material with carbon nanotubes, graphene, and inorganic nitrides. Additionally, the research developments in this field with prospective applications of CNF-based materials for supercapacitors, lithium-ion batteries, and solar cells are emphasized. Moreover, the emerging challenges of different cellulosic nanofibrils-based energy storage devices have been discussed in this review paper. Graphical abstract
... Comparison of various nanofibrillated cellulose (NFC) drying approaches[58][59][60]. ...
... Our different exponent could therefore be explained by a different particle interaction behavior due to the different concentrations and the shorter rod lengths. The morphological properties are dependent on the drying method (Peng et al. 2012) and this might also explain the difference. Calabrese et al. (2021a) report that extensional forces, described by the extensional rate ̇ , are four times more effective in aligning CNCs than shear forces, stating Δn ∼̇0 .9 ...
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Birefringence measurements of aqueous cellulose nanocrystal (CNC) suspensions are reported. Seven suspensions with concentrations between 0.7 and 1.3% per weight are sheared in a Taylor-Couette type setting and characterized using a birefringent measurement technique based on linear polarized light and acquisition with a polarization camera. Steady state measurements with shear rates up to 31 1/s show extinction angles of 23°–40° and birefringence in the order of 1e–5. The findings demonstrate the utility of CNC suspensions for flow birefringence studies.
... Normally, CNC is stored in the form of aqueous suspension due to the large number of hydrophilic groups on its surface (Sinquefield et al. 2020). It should be noted that CNC aqueous suspension tends to transform into gel state when its concentration exceeds a certain range which limits the further increase of its concentration (Peng et al. 2011). At present, CNCs are mainly stored, transported and used in the form of low-concentration aqueous suspension (0.1-10 wt%) that greatly limits their industrial application (Wang et al. 2019b). ...
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Nanocellulose is a renewable material with excellent properties. At present, nanocellulose powder is mainly prepared by high-cost spray drying, which severely limits its output and quality. In this paper, we propose an innovative method to prepare dispersible nanocellulose powder by simple precipitation and conventional evaporation. Potassium acetate was added to CNC (a kind of nanocellulose) suspension to precipitate and purify CNC. The added potassium acetate was dissolved in ethanol and removed. Then dispersible nanocellulose powder can be obtained by simple evaporation. In CNC purification, we discussed the combination of different electrolytes and CNCs. It was found that although the monovalent electrolytes lead to weak aggregation with CNC, the resulting dry CNC powder had the best dispersion. In CNC drying, we discussed the effects of different dispersants and different drying methods on the forming of dry CNC powder. It is revealed that ethanol is the best dispersant tested in this paper because it can only form a single hydrogen bond with CNC and is easy to evaporate. In the evaporation of CNC and ethanol mixture, it will not lead to the aggregation of CNC fibers. It is hopeful that the new method may greatly reduce the cost of the preparation of nanocellulose powder.
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When pulp and minerals are co-processed in suspension, the mineral acts as a grinding aid, allowing cost-effective production of mineral/microfibrillated cellulose (MFC) composite materials. This processing uses robust milling equipment and is practiced at industrial scale. The resulting products can be used in many applications, including as wet- and dry-strength aids in paper and board production. Previously, we have reported that use of these MFC composite materials in fiber-based applications allow generally improved wet and dry mechanical properties with concomitant opportunities for cost savings, property improvements, or grade developments. Mineral/MFC composites made with recycled pulp feedstocks were shown to offer at least equivalent strength aid performance to composites made using virgin fibers. Selection of mineral and fiber allows preparation of mineral/MFC composites with a range of properties. For example, the viscosity of such formulations was shown to be controlled by the shape factor of the mineral chosen, effective barrier formulations were prepared, and mineral/MFC composites with graphite as the mineral were prepared. High-solids mineral/MFC composites were prepared at 75% total solids (37% fibril solids). When resuspended and used for papermaking, these high-solids products gave equivalent performance to never-dried controls.
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Since endogenous pectin has been reported to improve water redispersibility of dried nanofibrillated cellulose (NFC), feasibility of using exogenous pectin to achieve such a purpose when NFC was prepared from a material with minute amount of pectin was investigated. Cabbage outer leaves, which are by‐product with low pectin content, were selected as the test material. Prior to defibrillation, commercial citrus pectin at different concentrations was autoclaved at 130 °C for 2 h with the cabbage. After hot air drying at 60 °C, dried NFC samples with 43‐44% (dry mass) cellulose and varying pectin contents were obtained. Freshly prepared NFC suspensions exhibited desirable gel‐like behaviour, while suspensions prepared from dried NFC did not. Aggregation of NFC was clearly seen from microstructural images although the contents of pectin were believed to be adequate. Hydrolysis of exogenous pectin during autoclaving into low molecular‐weight oligomers was noted to be responsible for such incapability.
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One of the main manufacturing challenges is to obtain dried cellulose nanofibrils (CNFs) so that they can be cost effectively transported to customers. This work presents a study on using two methods of drying: freeze drying and spray drying; these dried CNFs were then characterized. The dried CNFs from either freeze drying or spray drying could not recover their original state after simple re-dispersion in water. Compared to spray dried CNFs, the microstructure of the freeze dried CNFs remained in a better shape. This was because the packing of nanofibrils as a result of freeze drying was not as tight as that from spray drying. It was demonstrated by the lower final mass residue and crystallinity of the freeze-dried CNFs, which led to better re-dispersion in water. X-ray diffractometry proved the occurrence of aggregation/hornification of the dried CNFs with increased crystallinity. Time-dependent sedimentation confirmed that the dried CNFs were incapable of forming stable water-re-dispersible suspensions.
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Cellulose, consisting of β-anhydro-d-glucose units, is a natural, biodegradable, and versatile biopolymer with several applications in food and non-food systems. Cellulose is probably the most abundant biopolymer in the biosphere and is synthesized by multiple living organisms, ranging from some bacterial species to higher plants. Cellulose recovery was initially done from forest wood mainly. Other sources, including agro-industrial by-products, such as, fruit peels, husks, revealed to be potential reservoirs of cellulose. Recycling agro-industrial waste by recovering cellulose is an ideal strategy to mitigate the impact of food waste from agro-industrial activities. Moreover, the tremendous potential of cellulose nanomaterials has fueled researchers’ interest in developing environmentally friendly extraction techniques. The present review paper focuses on the recovery of nanocellulose from different agro-industrial by-products and reports the advantages of the extraction technique used, such as, the use of deep eutectic solvents, ultrasound, steam explosion, mild acids, reduced effluents, amongst others. The importance of characterizing the physico-chemical properties of nanocellulose from different sources is also discussed. It is expected that scientific findings presented in this paper will highlight the potential of agro-industrial wastes as cellulose reservoirs and the importance of physico-chemical characterization of nanocellulose.
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This review considers the most recent developments in supramolecular and supraparticle structures obtained from natural, renewable biopolymers as well as their disassembly and reassembly into engineered materials. We introduce the main interactions that control bottom-up synthesis and top-down design at different length scales, highlighting the promise of natural biopolymers and associated building blocks. The latter have become main actors in the recent surge of the scientific and patent literature related to the subject. Such developments make prominent use of multicomponent and hierarchical polymeric assemblies and structures that contain polysaccharides (cellulose, chitin, and others), polyphenols (lignins, tannins), and proteins (soy, whey, silk, and other proteins). We offer a comprehensive discussion about the interactions that exist in their native architectures (including multicomponent and composite forms), the chemical modification of polysaccharides and their deconstruction into high axial aspect nanofibers and nanorods. We reflect on the availability and suitability of the latter types of building blocks to enable superstructures and colloidal associations. As far as processing, we describe the most relevant transitions, from the solution to the gel state and the routes that can be used to arrive to consolidated materials with prescribed properties. We highlight the implementation of supramolecular and superstructures in different technological fields that exploit the synergies exhibited by renewable polymers and biocolloids integrated in structured materials.
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This study examined the effect of hemicellulose molecular structure on wettability and surface adhesion to urea–formaldehyde resin adhesives to better understand the complex adhesion process of wood biopolymers. Molecular structure of two hemicelluloses, such as arabinogalactan and xylan, was characterized using Fourier transform infrared, one-dimensional, and two-dimensional nuclear magnetic resonances. As a result, arabinogalactan had a hyperbranched structure, whereas xylan was more linear, which caused a distinctive morphology in their films, with the latter having a rougher surface. Further, the surface adhesion between hemicellulose and UF resins with various formaldehyde to urea molar ratios (1.0 and 1.6) was measured. The adhesion force and work of adhesion of arabinogalactan with different UF resins were found to be greater than those of xylan due to the former film’s higher surface free energy, more exposed OH groups, and smoother surface. In addition, 1.6 UF resins exhibited greater adhesion than 1.0 UF resins, regardless of the hemicellulose type, demonstrating that dispersion force was dominant in their molecular interactions.
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Interest in cellulose nanocrystal (CNC) recently has been growing significantly. Many applications have been developed for CNC and appropriate procedures to handle the CNC suspensions are critical for these applications. In this study, we explored a method evaluating CNC suspensions based on rheological property characterization. We used a rotational viscometer to characterize CNC suspensions at concentrations of 3, 4, 5, and 6 wt.%. We collected primary readings from the rotational viscometer, including spindle rotation speed and torque, to generate apparent viscosity and shear rate for CNC suspensions. We applied three different methods summarized from the literature to calculate apparent viscosity and real shear rate. We critically analyzed differences among calculation results from the three methods. Shearing thinning behaviors obeyed the power law flow model for all CNC suspensions in the shear rate tested. At different concentrations, consistency and flow behavior indices in the model differed in the measured shear rate range. With the same shear rate, higher concentration CNC suspension had a higher apparent viscosity. The apparent viscosity of the CNC suspension was associated with its weight concentration in a power law relationship. This study indicated that a rotational viscometer can be used as a quality control tool for characterizing the rheological properties of the CNC suspensions. We made recommendations for using appropriate calculation methods to obtain shear rate and apparent viscosity of CNC suspensions from the primary readings of a rotational viscometer under different situations.
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Because of dysprosium's unique physical and chemical properties and limited supply, the price of rare earth dysprosium has been high in recent years. Therefore, the study of the method of high efficiency selective separation of dysprosium has the double value of scientific research and practical economy. In this paper, we used periodic cellulose nanocrystals as the basic structure, polyethylenimine and graphene oxide were introduced, combined with imprinting technology, to construct porous imprinted aerogel and use it for selective adsorption of Dy(III). The physical and chemical properties were characterized by SEM, TEM, FT-IR and TGA. It was proved that both polyethylenimine and graphene oxide were crosslinked effectively with cellulose nanocrystals. Adsorption experiments showed that the composite imprinted aerogel could selectively adsorb dysprosium effectively, and the maximum adsorption capacity for Dy(III) was 36.495 mg g − 1 . The reproducibility experiment showed that aerogel had good regeneration ability. In conclusion, cellulose nanocrystals aerogel, which is environmentally friendly, efficient and repeatable, is expected to provide a new direction for the recovery of rare earth elements.
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A lightweight acoustic composite foams with unique sound absorption feature is reported, that is, the foam acoustic composite demonstrates surprisingly stable sound absorption performance in a wide bandwidth of frequency. The unique acoustic properties are attributed to the highly exfoliated nano-layered biocarbon nucleation, derived from the pyrolytic pinus resinosa, with tailoring the foam structure and properties. Polystyrene (PS) composite foams with porous graphitic biocarbon are obtained by sequestering recycled supercritical carbon dioxide assisted with torsion extrusion technology. Unique design concept is validated and implemented in the torsion induced extrusion process, with good mixing and thermal management, offering a suitable environment for the nucleation, uniform growth and stability of the cells on the foam structures. The presence of porous graphitic nano-layered characteristics of biocarbon in the composition changes the sound insulation behavior from resonant absorber of pure PS closed cell foam to stable acoustic performance over a wide range in high frequency band (3.5-6.4 kHz) while preserving the closed cell structure. This allows the tailoring of cell structures and properties with varying renewable carbon content, so as to better adapt to a broadband sound absorption applications including absorbing panels, anechoic chamber with high accuracy and aircraft acoustic stealth technology. This article is protected by copyright. All rights reserved
Chapter
Natural cellulose fibers have attracted significant interest for manufacturing advanced polymer composites due to their environmental friendliness (renewability and biodegradability), easy availability, high stiffness and strength, easy processability, and modifiable surfaces. Many applications have been developed and more are being explored for cellulose fiber reinforced polymer composites. In different regions in the world the focus is on developing and usingdifferent cellulose based polymer composites for a variety of applications. For examples, In North America, wood based cellulose fibers have been extensively researched for manufacturing polymer composites in applications in the construction sector, such as outdoor decking and siding. In Europe, these composites are being investigated for fuel efficient and recyclable automotive components. In India and South America jute and sugar cane fiber reinforced polymers are being investigated for structural applications in housing. In this chapter, the physical, mechanical, and chemical properties of cellulose fibers of different origins will be presented. The processes used to manufacture cellulose fiber reinforced thermoplastic composites will then be introduced followed by the performance of these composites. A major challenge in using natural fibers as reinforcement for polymers is the poor adhesion between the fibers and the matrices. As a result, surface modification of the fibers is an active area of research and development and is comprehensively covered in this Chapter. Another area of active investigation is the use of nano-fibers as reinforcements. The status and challenges in this area are also summarized.
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Although nanocellulose is an eco-friendly, high-performance raw material provided by nature, the agglomeration of nanocellulose that occurs during the drying process is the biggest obstacle to its advanced materialization and commercialization. In this study, a facile and simple nanocellulose drying system was designed using lignin, which is self-assembled together with cellulose in natural wood, as an eco-friendly additive. The addition of lignin not only minimized aggregation during the drying and dehydration process of nanocellulose but also ensured excellent redispersion kinetics and stability. In addition, the added lignin could be removed through a simple washing process. Through FTIR, XRD, TGA, tensile and swelling tests, it was confirmed that the addition of lignin enabled the reversible restitution of the nanocellulose physicochemical properties to the level of pristine never-dried nanocellulose in drying, redispersion, and polymer processing processes.
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Despite increasing interest in using nanofibrillated cellulose (NFC) as food thickener and emulsifier, poor water redispersibility of dried NFC, which is form suitable for practical utilization, significantly limits such applications. Studies are lacking on preparation of dried NFC with superior redispersibility. The present study therefore proposed and examined strategies to improve water redispersibility of spray dried NFC via the use of selected co-carriers, i.e., gum Arabic with/without xanthan gum, carboxymethyl cellulose or pectin. Synergistic interactions between NFC and co-carriers, as confirmed by X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra, helped prevent NFC agglomeration during spray drying. All reconstituted spray-dried NFC/co-carriers suspensions exhibited shear-thinning and gel-like behaviors, thus supporting the use of such suspensions as thickener and emulsifier. Spray-dried NFC with 80% gum Arabic and 20% xanthan gum (SD-NFC/GA20XG) resulted in suspension with highest viscosity; the suspension also performed best at recovering viscous characteristics of NFC. Water thickened by SD-NFC/GA20XG had strongest shear-thinning behavior, indicating that SD-NFC/GA20XG suspension resulted in smoothest mouth feel and easiest swallowing. Such observations were supported by XRD patterns of SD-NFC/GA20XG, which suggested that its relative crystallinity was the lowest. Its FTIR spectra also showed the highest intensity of –OH bending and carbonyl bands, which are directly related to water adsorption capability of NFC. Use of reconstituted SD-NFC/GA20XG as emulsifier also resulted in highest stability for oil-in-water (O/W) Pickering emulsion during storage for up to 30 days.
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Flexible devices serve as important intelligent interfaces in various applications involving health monitoring, biomedical therapies, and human–machine interfacing. To address the concern of electronic waste caused by the increasing usage of electronic devices based on synthetic polymers, bio‐origin materials that possess environmental benignity as well as sustainability offer new opportunities for constructing flexible electronic devices with higher safety and environmental adaptivity. Herein, the bio‐source and unique molecular structures of various types of natural bio‐origin materials are briefly introduced. Their properties and processing technologies are systematically summarized. Then, the recent progress of these materials for constructing emerging intelligent flexible electronic devices including energy harvesters, energy storage devices, and sensors are introduced. Furthermore, the applications of these flexible electronic devices including biomedical implants, artificial e‐skin, and environmental monitoring are summarized. Finally, future challenges and prospects for developing high‐performance bio‐origin material‐based flexible devices are discussed. This review aims to provide a comprehensive and systematic summary of the latest advances in the natural bio‐origin material‐based flexible devices, which is expected to offer inspirations for exploitation of green flexible electronics, bridging the gap in future human–machine–environment interactions.
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In this work, the viability of contact dewatering of cellulose nanofibrils (CNFs) and lignin-containing cellulose nanofibrils (LCNFs) was tested to achieve nanoscale morphology of dried fibers on wood particles with varying CNF and LCNF contents after dewatering and oven drying. Nanoscale dimensions of dried CNFs and LCNFs were observed on the surface of wood particles and mechanical testing of WF-CNF and WF-LCNF furnish-incorporated poly(lactic) acid (PLA) composites showed similar or better properties than PLA mixed with spray-dried CNFs. Analysis of theoretical energy required to dry CNFs and LCNFs via contact dewatering showed a considerable reduction compared to non-dewatered CNFs.
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Cellulose nanofibers (CNF) are demonstrated as an effective tool for converting electrodeposits into more easily detachable dendritic deposits useful in recycling zinc ion batteries via electrowinning. The incorporation of CNF...
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Sugarcane bagasse fiber cellulose nanocrystals (SBFCNC) and microcrystalline cellulose-derived-cellulose nanocrystals (MCC-CNC) were extracted from sugarcane bagasse fiber (SBF; an agricultural waste) and microcrystalline cellulose (MCC), respectively. Both SBFCNC and MCC-CNC were synthesized using sulfuric acid hydrolysis followed by the freeze-drying method. Both MCC-CNC and SBFCNC show stable suspension in water with zeta potential values of – 40.5 mV and – 42.2 mV, respectively. Transmission electron microscopy (TEM) analysis revealed that the SBFCNC has a higher aspect ratio (l/d = 65) compared to the MCC-CNC (l/d = 25). The poly(lactic acid) (PLA) nanocomposites containing of MCC-CNC and SBFCNC was prepared using solvent casting method, and the films are highly amorphous as evidenced from the differential scanning calorimetry (DSC) study. The tensile strength of PLA/SBFCNC-10 is higher than that of PLA/MCC-CNC-10 films. Thermogravimetric analysis (TGA) results showed that the thermal stability of PLA was improved significantly by the incorporation of MCC-CNC and SBFCNC. Poly(lactic acid)/SBFCNC-15 nanocomposites exhibited higher UV shielding properties (i.e., a UV blocking ratio of 0.63–0.66 in the UVA, UVB, and UVC regions) compared to PLA/MCC-CNC-15 nanocomposites (a UV blocking ratio in the range of 0.38–0.54). Sugarcane bagasse fiber cellulose nanocrystal is a potential biofiller that can provide good thermal stability and UV shielding properties for green bionanocomposites, which can give it an opportunity for food packaging applications.
Chapter
Nanocelluloses are a very promising material that has been widely explored for the most diverse applications. The pursuit for sustainable and environmentally friendly materials is in line with the nature of nanocelluloses and therefore they have emerged as the perfect candidate for plastics substitution, food additive, rheology controller, 3D printing of diverse structures, among many other possibilities. This derives from their interesting characteristics, such as reduced size and high specific surface area, high tensile strength, crystallinity and transparency, and from the fact that, such as cellulose, they are obtained from renewable sources, with relative ease for functionalization in order to obtain desired specificities. Thus, the industry is trying to react and effectively respond to the exponential growth of published research in the last years, and therefore new facilities (not only lab and pilot plants but already industrial sites) have been producing nanocelluloses. This new fibrous materials can be obtained from different raw-materials by different methodologies, leading to different types of nanocelluloses with, obviously, different characteristics. Nonetheless, technical and economical constraints have been addressed, such as the high energy demand or the clogging of homogenizers/microfluidizers. This chapter intends to present a review addressing the main features related to the production, characterization and market of nanocelluloses and providing additional information regarding the vast literature published in these domains.
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Microfibrillated cellulose (MFC) is prepared by subjecting dilute slurries of cellulose fibers to repeated high-pressure homogenizing action. A highly microfibrillated product will have a gel-like appearance at 2% concentration in water. Such gels have pseudoplastic viscosity properties and are very fluid when stirred at high shear rate. The relative viscosity of 2% MFC dispersions may be used as a measure of the degree of homogenization or microfibrillation of a given wood cellulose pulp. The water retention value of an MFC product can also be used as an indicator for degree of homogenization. Structurally, MFC appears to be a web of interconnected fibrils and microfibrils, the latter having diameters in the range 10-100 nm as observed in scanning and transmission electron micrographs. Chemical studies have revealed that MFC is only moderately degraded, while being greatly expanded in surface area. The accessibility of cellulose in MFC is only moderately degraded, while being greatly expanded in surface area. The accessibility of cellulose in MFC toward chemical reagents is greatly increased. Higher reactivity was demonstrated in dilute cupriethylenediamine solubility, triphenylmethylation, acetylation, periodate oxidation, and mineral acid and cellulase enzyme hydrolysis rates. 16 references, 8 figures, 7 tables.
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Pure β-carotene was encapsulated in 25 Dextrose Equivalent maltodextrin by three drying processes (spray, freeze and drum). Stability was studied at 11% and 32% RH and 25°C, 35°C and 45°C. No significant influence of %RH was observed on the retention of β-carotene. Oxidation followed first order kinetics with an initial fast first order reaction followed by a second much slower first order reaction period. Although drum-drying caused more initial loss in drying, the lower surface carotenoids and larger particle size resulted in greater stability as compared to the other methods. The chromametric measurements of “L” and “a” corresponded to the other kinetics and indicated that the first period rapid loss corresponded to the oxidation of surface carotenoids.
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This paper presents the types of nanomaterials whose technology requires drying during processing. The methods of drying of three groups of nanomaterials are discussed: nanoparticles, nanolayers (nanofilms), and nanoporous materials. Principally the method of spray drying using ultrasonic nebulizers and electrospraying is presented for the first group. The Langmuir-Blogget technique is presented for the second group. The method of supercritical drying and the solvent replacement technique is described for the third group. Technological aspects of the presentedmethods are also briefly described.
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The crystal and molecular structure together with the hydrogen-bonding system in cellulose Ibeta has been determined using synchrotron and neutron diffraction data recorded from oriented fibrous samples prepared by aligning cellulose microcrystals from tunicin. These samples diffracted both synchrotron X-rays and neutrons to better than 1 Angstrom resolution (>300 unique reflections; P2(1)). The X-ray data were used to determine the C and 0 atom positions, The resulting structure consisted of two parallel chains having slightly different conformations and organized in sheets packed in a "parallel-up" fashion, with all hydroxymethyl groups adopting the tg conformation. The positions of hydrogen atoms involved in hydrogen-bonding were determined from a Fourier-difference analysis using neutron diffraction data collected from hydrogenated and deuterated samples. The hydrogen atoms involved in the intramolecular O3...O5 hydrogen bonds have well-defined positions, whereas those corresponding to 02 and 06 covered a wider volume, indicative of multiple geometry with partial occupation. The observation of this disorder substantiates a recent infrared analysis and indicates that, despite their high crystallinity, crystals of cellulose Ibeta have an inherent disorganization of the intermolecular H-bond network that maintains the cellulose chains in sheets.
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Abstract Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.
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Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.
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Cellulose - online first Microfibrillated cellulose (MFC), also referred to as nanocellulose, is one of the most promising innovations for forest sector. MFC is produced by fibrillating the fibres under high compression and shear forces. In this study we evaluated the worker exposures to particles in air during grinding and spray drying of birch cellulose. Processing of MFC with either a friction grinder or a spray dryer did not cause significant exposure to particles during normal operation. Grinding generated small amount of particles, which were mostly removed by fume hood. Spray dryer leaked particles when duct valve was closed, but when correctly operated the exposure to particles was low or nonexistent. To assess the health effects of the produced MFC, mouse macrophages and human monocyte derived macrophages were exposed to MFC and the viability and cytokine profile of the cells were studied thereafter. No evidence of inflammatory effects or cytotoxicity on mouse and human macrophages was observed after 6 and 24 h exposure to the materials studied. The results of toxicity studies suggest that the friction ground MFC is not cytotoxic and does not cause any effects on inflammatory system in macrophages. In addition, environmental safety of MFC was studied with ecotoxicity test. Acute environmental toxicity assessed with kinetic luminescent bacteria test showed high NOEC values (>100 mg/l) for studied MFC. However, MFC disturbed Daphnia magna mobility mechanically when the test was performed according to the standard procedure.
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This paper provides an overview of recent progress made in the area of cellulose nanofibre-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibres (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterisation of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibres covered are those extracted from plants by acid hydrolysis (nanowhiskers), mechanical treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, analysis of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymerisation from the surface of cellulose nanowhiskers by atom transfer radical polymerisation and ring opening polymerisation, and methods to analyse the dispersion of nanowhiskers. The applications and new advances covered in this review are the use of cellulose nanofibres to reinforce adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocomposites and the use of all-cellulose nanocomposites for enhanced coupling between matrix and fibre. A comprehensive coverage of the literature is given and some suggestions on where the field is likely to advance in the future are discussed.
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The hydrogen-bonding network and molecular orientation in cellulose vary widely that gives rise to cellulose polymorphs or allomorphs, depending on the respective source, method of extraction, or treatment. Microcrystalline cellulose (MCC) offers a significant opportunity for multiple uses in pharmaceutical industry as a tablet binder, in food applications as a texturizing agent and fat replacer, and also, as an additive in paper and composites applications. The main process for the isolation of cellulose nanocrystal (CN) from cellulose fibers is based on acid hydrolysis. The sulfuric and hydrochloric acids have been extensively used for CN preparation, but phosphoric and hydrobromic acids have also been employed for such purposes. The cellulose nanocrystal generated from hydrochloric acid hydrolysis and then treated with sulfuric acid solution has the same particle size as those directly obtained from sulfuric acid hydrolysis.