Use of switchable ionic liquid (SIL) pulp offers an efficient and greener technology to produce nanofibers via ultrafine grinding. In this study, we demonstrate that SIL pulp opens up a mechanically efficient route to the nanofibrillation of wood pulp, thus providing both a low cost and chemically benign route to the production of cellulose nanofibers. The degree of fibrillation during the process was evaluated by viscosity and optical microscopy of SIL treated, bleached SIL treated and a reference pulp. Furthermore, films were prepared from the fibrillated material for characterization and tensile testing. It was observed that substantially improved mechanical properties were attained as a result of the grinding process, thus signifying nanofibrillation. Both SIL treated and bleached SIL treated pulps were fibrillated into nanofibers with fiber diameters below 15 nm thus forming networks of hydrophilic nature with an intact crystalline structure. Notably, it was found that the SIL pulp could be fibrillated more efficiently than traditional pulp since nanofibers could be produced with more than 30% less energy when compared to the reference pulp. Additionally, bleaching reduced the energy demand by further 16%. The study demonstrated that this switchable ionic liquid treatment has considerable potential in the commercial production of nanofibers due to the increased efficiency in fibrillation.

The objective of this work was to find a rapid, high-yield process to obtain an aqueous stable colloid suspension of cellulose nanocrystals/whiskers. Large quantities are required since these whiskers are designed to be extruded into polymers in the production of nano-biocomposites. Microcrystalline cellulose (MCC), derived from Norway spruce (Picea abies), was used as the starting material. The processing parameters have been optimized by using response surface methodology. The factors that varied during the process were the concentration of MCC and sulfuric acid, the hydrolysis time and temperature, and the ultrasonic treatment time. Responses measured were the median size of the cellulose particles/whiskers and yield. The surface charge as calculated from conductometric titration, microscopic examinations (optical and transmission electron microscopy), and observation of birefringence were also investigated in order to determine the outcome (efficiency) of the process. With a sulfuric acid concentration of 63.5% (w/w), it was possible to obtain cellulose nanocrystals/whiskers with a length between 200 and 400 nm and a width less than 10 nm in approximately 2 h with a yield of 30% (of initial weight).

This study confirms the enzyme-mediated phosphorylation of cellulose nanofibers (CNF) by using hexokinase and adenosine-5’-triphosphate (ATP) in the presence of Mg-ions, resulting in a phosphate group’s creation predominantly at C-6-O positioned hydroxyl groups of cellulose monomer rings. A proof-of-concept is provided using 12C CPMAS, 31P MAS NMR, ATR-FTIR and XPS analyzing methods. The degree of substitution is determined for the first time by ATR-FTIR spectroscopy being in a correlation with XPS and potentiometric titration results. From the thermal degradation measurements using TGA, the C-6-O phosphorylation was found to noticeably prevent the CNF derivatives from weight loss in the pyrolysis process, thus, providing them flame-resistance functionality. Furthermore, phosphorylation significantly enhanced adsorption capacity of Fe3+ ions making them interesting for fabrication of biobased filters and membranes. Finally, the biomimetic growth of Ca-P crystals (hydroxyapatite) in simulated body fluid was characterized by SEM and showing further practicability for biomedical materials.

Cellulose nanofibrils (CNFs), unique and promising natural materials have gained significant attention recently for biomedical applications, due to their special biomechanical characteristics, surface chemistry, good biocompatibility and low toxicity. However, their long bio-persistence within organisms may provoke chronic immune reactions and this aspect of CNFs has not been studied to date. Therefore, the aim of this work was to examine and compare the biocompatibility and immunomodulatory properties of CNFs in vitro. CNFs (diameters of 10-70nm; lengths of a few microns) were prepared from Norway spruce (Picea abies) by mechanical fibrillation and high pressure homogenisation. L929 cells, rat thymocytes or human peripheral blood mononuclear cells (PBMNCs) were cultivated with CNFs. None of the six concentrations of CNFs (31.25µg/ml – 1mg/ml) induced cytotoxicity and oxidative stress in the L929 cells, nor induced necrosis and apoptosis of the thymocytes and PBMNCs. Higher concentrations (250µg/ml – 1mg/ml) slightly inhibited the metabolic activities of the L929 cells as a consequence of inhibited proliferation. The same concentrations of CNFs suppressed the proliferation of PBMNCs to phytohemaglutinine, a T-cell mitogen, and the process was followed by down-regulation of interleukin-2 (IL-2) and interferon-γ (IFN-γ) production. The highest concentration of CNFs inhibited IL-17A but increased IL-10 and IL-6 production. The secretions of the inflammatory cytokines, IL-1β and the tumor necrosis factor-α (TNF-α) as well as Th2 cytokine (IL-4), remained unaltered. In conclusion, the results suggest that these CNFs are biocompatible, non-inflammatory and non-immunogenic nanomaterial. Higher concentrations seem to be tollerogenic to the immune system, a characteristic very desirable for implantable biomaterials.

Nanofibrillated cellulose (NFC) is a type of nanomaterial based on renewable resources and produced by mechanical disintegration without chemicals. NFC is a potential reinforcing material with a high surface area and high aspect ratio, both of which increase reinforcement on the nanoscale. The raw materials used were unbleached and bleached bamboo organosolv pulp. Organosolv pulping is a cleaner process than other industrial methods (i.e. Kraft process), as it uses organic solvents during cooking and provides easy solvent recovery at the end of the process. The NFC was produced by treating unbleached and bleached bamboo organosolv pulps for 5, 10, 15 and 20 nanofibrillation cycles using the grinding method. Chemical, physical and mechanical tests were performed to determine the optimal condition for nanofibrillation. The delamination of the S2 layer of the fibers during nanofibrillation contributed to the partial removal of amorphous components (mainly lignin), which have low polarity and improved the adhesion of the fibers, particularly the unbleached cellulose. The transverse modulus of elasticity of the unbleached NFC was highest after 10 nanofibrillation cycles. Further treatment cycles decreased the modulus due to the mechanical degradation of the fibers. The unbleached NFC produced by 10 cycles have a greater transverse modulus of elasticity, the crystallite size showed increase with the nanofibrillation, and after 5 nanofibrillation cycles, no differences are observed in the morphology of the fibers.

Nanocellulose was successfully extracted from five different lignocellulosic biomass sources viz. banana rachis, sisal, kapok, pineapple leaf and coir using a combination of chemical treatments such as alkaline treatment, bleaching and acid hydrolysis. The shape, size and surface properties of the nanocellulose generally depend on the source and hydrolysis conditions. A comparative study of the fundamental properties of raw material, bleached and nanocellulose was carried out by means of Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, birefringence, X-ray diffraction, inverse gas chromatography and thermogravimetric analysis. Through the characterization of the nanocellulose obtained from different sources, the isolated nanocellulose showed an average diameter in the range of 10–25 nm, high crystallinity, high thermal stability and a great potential to be used with acid coupling agents due to a predominantly basic surface. This work provides an insight into the effective utilization of a variety of plant biomass as a potential source for nanocellulose extraction.

Water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by carboxymethylation (c) and mechanical disintegration (m). Two routes were examined by altering the sequence of the chemical and mechanical treatment, leading to four different products: RBP-m and RBP-mc (route 1), and RBP-c and RBP-cm (route 2). The occurrence of the carboxymethylation reaction was confirmed by FT-IR spectrometry and 13C solid state NMR (13C CP-MAS) spectroscopy with the appearance of characteristic signals for the carboxylate group at 1,595 cm-1 and 180 ppm, respectively. The chemical modification reduced the crystallinity of the products, especially for those of route 2, as shown by XRD experiments. Also, TGA showed a decrease in the thermal stability of the carboxymethylated products. However, sedimentation tests revealed that carboxymethylation was critical to obtain water-redispersible powders: the products of route 2 were easier to redisperse in water and their aqueous suspensions were more stable and transparent than those from route 1. SEM images of freeze-dried suspensions from redispersed RBP powders confirmed that carboxymethylation prevented irreversible agglomeration of cellulose fibrils during drying. These results suggest that carboxymethylated and mechanically disintegrated RBP in dry form is a very attractive alternative to conventional NFC aqueous suspensions as starting material for derivatization and compounding with (bio)polymers.

Bionanocomposites of hydroxypropyl cellulose (HPC) and nanofibrillated cellulose (NFC) were prepared by solution casting. The various NFC were in form of powders and were prepared from refined, bleached beech pulp (RBP) by mechanical disintegration, optionally combined with a pre- or post mechanical carboxymethylation. Dynamic mechanical analysis (DMA) and tensile tests were performed to compare the reinforcing effects of the NFC powders to those of their never-dried analogues. For unmodified NFC powders an inferior reinforcing potential in HPC was observed that was ascribed to severe hornification and reagglomeration of NFC. In contrast, the composites with carboxymethylated NFC showed similar behaviors, regardless of the NFC suspensions being dried or not prior to composite preparation. SEM characterization confirmed a homogeneous dispersion of dried, carboxymethylated NFC within the HPC matrix. These results clearly demonstrate that drying of carboxymethylated NFC to a powder does not decrease its reinforcing potential in (bio)nanocomposites.

Cellulose acetate (CA) fibers were electrospun on a mesh template to create specific surface and pore structures for membrane applications. The mesh template CA fiber mats were impregnated with cellulose nanocrystals at varying weight percentages. The membranes showed nanotextured surfaces and improved mechanical properties post impregnation. More importantly, the hydrophilicity of the original CA fibers was increased from a hydrophobic contact angle of 102°–0° thereby creating an anti-fouling membrane surface structure. The membranes showed rejection of 20–56% for particles of 0.5–2.0 μm, indicating potential of these membranes in rejecting microorganisms from water. Furthermore, high rejection of dyes (80–99%) by adsorption and potential application as highly functional affinity membranes was demonstrated. These membranes can therefore be utilized as all-cellulose, green, scalable and low cost high flux membranes (> 20,000 LMH) for water cleaning applications in food industry where microorganisms and charged contaminants are to be removed.

The effect of treatment of regenerated cellulose fibres by cellulose nanocrystals on the moisture absorption of the fibres as well as on fibre–epoxy resin adhesion has been investigated. Nanocrystals were deposited on the fibres using γ-methacryloxypropyltrimethoxysilane (MPS) as coupling agent. Water absorption tests performed on fibres showed that, at 64% relative humidity, treatment by the coupling agent decreased the water uptake by a factor of two compared with untreated fibres, whereas deposition of cellulose nanocrystals (CNC) on fibres treated with MPS (FMMPS) did not further increase the water absorption despite the hydrophilic character of the CNC. This result was confirmed by monitoring fibre swelling using contact angle measurements. Indeed, it was found that FMMPS presented the same contact angle with glycerol before and after CNC deposition, being higher than that obtained for untreated fibres. The tensile strength and stiffness of fibres were not affected by moisture after either treatment, but nanocrystal deposition enhanced the fibre–epoxy resin adhesion, as revealed by results of pull-out tests performed on fibre bundles at 64% relative humidity.

This paper describes an approach to manufacture hierarchical composites from environmentally friendly materials by grafting cellulose whiskers onto regenerated cellulose fibers (Cordenka 700). Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy and X-ray diffraction analysis were performed to verify the degree of modification. The mechanical properties of the unmodified and modified fibers were analyzed using fiber bundle tensile static and loading-unloading tests. To show the effect of cellulose whiskers grafting on the Cordenka fibers, epoxy based composites were manufactured and tensile tests done on transverse uni-directional specimens. The mechanical properties were significantly increased by fiber modification and addition of the nano-phase into composite reinforced with micro-sized fibers.

There is a recent interest in producing cellulose nanofibers with different surface properties from unbleached cellulose pulps for economic and environmental reasons. In the current study we investigated the use of xylanase pretreatment on two types of unbleached rice straw pulps, namely, soda and neutral sulfite, and their fibrillation to nanofibers using ultrafine grinding. The effect of xylanase pretreatment on the fibrillation progress, energy consumption, and nanofiber dimensions was studied. In addition, mechanical properties, water contact angle, water absorption, and roughness of produced nanopapers were studied. Although very thin nanofibers with a homogenous width could be isolated from both xylanase-treated and untreated pulps, the xylanase pretreatment resulted in faster fibrillation. In addition, nanopapers prepared from xylanase-treated nanofibers had better mechanical properties than those isolated from the untreated pulps. The energy consumption during fibrillation depended on the type of pulp; a slightly lower energy consumption (~ 8%) was recorded for xylanase-treated soda pulp while a higher energy consumption (~ 21%) was recorded for xylanase-treated neutral sulfite pulp compared to the untreated pulps.

In this study, the effect of pectin extraction method on the properties of cellulose nanofibers (CNFs) isolated from sugar beet pulp (SBP) was studied. Pectin was extracted by the industrially practiced method by sulfuric acid hydrolysis or by enzymatic hydrolysis using a cellulase/xylanase enzymes mixture. The CNFs were then isolated by high-pressure homogenization and investigated in terms of their chemical composition, crystallinity, size, degree of polymerization, and re-dispersion in water after freeze-drying. The mechanical properties and surface characteristics of CNF films were also studied. The results showed that fibrillation of the de-pectinated SBP was more efficient for the acid hydrolyzed SBP. CNFs from the acid-hydrolyzed SBP had a slightly wider diameter, higher crystallinity, viscosity, and α-cellulose content but a lower degree of polymerization than CNFs from the enzyme-hydrolyzed SBP. Owing to the presence of more residual hemicelluloses in the CNFs from the enzyme-hydrolyzed SBP, the CNFs had higher re-dispersion ability in water. CNF films from enzyme-hydrolyzed SBP displayed slightly better mechanical properties and higher water contact angle than acid-hydrolyzed CNF films.

Barrier, mechanical and thermal properties of porous paper substrates dip-coated with nanocellulose (NC) were studied. Sorbitol plasticizer was used to improve the toughness, and citric acid cross-linker to improve the moisture stability of the coatings. In general, the addition of sorbitol increased the barrier properties, maximum strength and toughness as well as the thermal stability of the samples when compared to the non-modified NC coatings. The barrier properties significantly improved, especially for plasticized NC coating’s, where the oxygen permeability value was as low as 0.7 mL μm day⁻¹ m⁻² kPa⁻¹ at 49% RH and the water vapor permeability was reduced by 60%. Furthermore, we found that the cross-linked plasticized NC coating had a smoother surface (50% lower roughness) compared to non-modified ones. This study shows that the environmentally friendly additives sorbitol and citric acid had positive effects on NC coating properties, increasing its potential use in paper-based packaging applications.

A simple method for preparing redispersible nanofibers from sugar beet residue and their use as a well-dispersed reinforcement for a polyvinyl alcohol (PVA) matrix is reported. It is known that the redispersion of dried cellulose nanofibers is difficult because of the formation of strong hydrogen bonds between the nanofibers. The results show that the properties of the initial sugar beet nanofiber suspension can be recovered without the use of chemical modification or additives with higher pectin and hemicellulose content. Undried and redispersed nanofibers with and without pectin were used as nanocomposite reinforcement with PVA. The redispersed nanofibers were as good reinforcements as the undried nanofibers. The tensile strength and elastic modulus of the nanocomposites with the redispersed sugar beet nanofibers were as good as those of the nanocomposites with undried nanofibers. Interestingly, the nanofiber dispersion in the PVA matrix was better when sugar beet nanofibers containing pectin and hemicellulose were used as reinforcements.

Bio-based continuous fibers were prepared by melt spinning cellulose acetate butyrate (CAB), cellulose nanocrystals (CNC) and triethyl citrate. A CNC organo-gel dispersion technique was used and the prepared materials (2 and 10 wt% CNC) were melt spun using a twin-screw micro-compounder and drawn to a ratio of 1.5. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young's modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance

Fiber mat materials based on cellulose natural fibers combines a useful set of properties, including renewability, stiffness, strength and dielectric insulation, etc. The dominant in-plane fiber orientation ensures the in-plane performance, at the expense of reduced out-of-plane behavior, which has not been studied as extensively as the in-plane behavior. Quantitative use of X-ray micro-computed tomography and strain analyses under in-situ loading open up possibilities to identify key mechanisms responsible for deformation. In the present investigation, focus is placed on the out-of-plane deformation under compressive loading of thick, high density paper, known as pressboard. The samples were compressed in the chamber of a microtomographic scanner. 3D images were captured before and after the loading the sample. From sequential 3D images, the strain field inside the material was calculated using digital volume correlation. Two different test pieces were tested, namely unpolished and surface polished ones. The first principal strain component of the strain tensor showed a significant correlation with the density variation in the material, in particular on the top and bottom surfaces of unpolished samples. The manufacturing-induced grooves generate inhomogeneities in the microstructure of the surface, thus creating high strain concentration zones which give a sensible contribution to the overall compliance of the unpolished material. More generally, the results reveal that, on the micrometer scale, high density fiber pressboard behaves as a porous material rather than a low density fiber network.

Cellulose nanofibrils (CNFs) are top-down nanomaterials obtainable from abundant lignocelluloses. Despite recent advances in processing technologies, the effects of variations in the lignocellulose structure and composition on CNF isolation and properties are poorly understood. In this study, we compared the isolation of CNFs from tension wood (TW) and normal wood (NW) from Populus tremula (aspen). The TW has a higher cellulose content, native cellulose fibrils with a larger crystalline diameter, and less lignin than the NW, making it an interesting material for CNF isolation. The wood powders were oxidized directly by 2,2,6,6-tetramethylpiperidin-1-oxyl, and the morphology and mechanical behaviors of the nanofibril suspensions and networks were characterized. The TW was more difficult to fibrillate by both chemical and mechanical means. Larger nanofibrils (5–10 nm) composed of 1.2 nm structures were present in the TW CNFs, whereas the NW samples contained more of thin (1.6 nm) structures, which also comprised 77% of the solid yield compared to the 33% for TW. This difference was reflected in the TW CNF networks as decreased transmittance (15% vs. 50%), higher degree of crystallinity (85.9% vs. 78.0%), doubled toughness (11 MJ/m³) and higher elongation at break (12%) compared to NW. The difference was ascribed to greater preservation of the hierarchical, more crystalline microfibril structure, combined with a more cellulose-rich network (84% vs. 70%). This knowledge of the processing, structure, and properties of CNFs can facilitate the breeding and design of wood feedstocks to meet the increasing demand for nanoscale renewable materials.

The link between wood and corresponding cellulose nanofiber (CNF) behavior is complex owing the multiple chemical pretreatments required for successful preparation. In this study we apply a few pretreatments on aspen wood and compare the final CNF behavior in order to rationalize quantitative studies of CNFs derived from aspen wood with variable properties. This is relevant for efforts to improve the properties of woody biomass through tree breeding. Three different types of pretreatments were applied prior to disintegration (microfluidizer) after a mild pulping step; derivatizing TEMPO-oxidation, carboxymethylation and non-derivatizing soaking in deep-eutectic solvents. TEMPO-oxidation was also performed directly on the plain wood powder without pulping. Obtained CNFs (44–55% yield) had hemicellulose content between 8 and 26 wt% and were characterized primarily by fine (height ≈ 2 nm) and coarser (2 nm < height < 100 nm) grade CNFs from the derivatizing and non-derivatizing treatments, respectively. Nanopapers from non-derivatized CNFs had higher thermal stability (280 °C) compared to carboxymethylated (260 °C) and TEMPO-oxidized (220 °C). Stiffness of nanopapers made from non-derivatized treatments was higher whilst having less tensile strength and elongation-at-break than those made from derivatized CNFs. The direct TEMPO-oxidized CNFs and nanopapers were furthermore morphologically and mechanically indistinguishable from those that also underwent a pulping step. The results show that utilizing both derivatizing and non-derivatizing pretreatments can facilitate studies of the relationship between wood properties and final CNF behavior. This can be valuable when studying engineered trees for the purpose of decreasing resource consumption when isolation cellulose nanomaterials.

The aim of this study was to develop cellulose nanofibers with hydrophobic surface characteristics using chemical modification. Kenaf fibers were modified using acetic anhydride and cellulose nanofibers were isolated from the acetylated kenaf using mechanical isolation methods. Fourier transform infrared spectroscopy (FTIR) indicated acetylation of the hydroxyl groups of cellulose. The study of the dispersion demonstrated that acetylated cellulose nanofibers formed stable, well-dispersed suspensions in both acetone and ethanol. The contact angle measurements showed that the surface characteristics of nanofibers were changed from hydrophilic to more hydrophobic when acetylated. The microscopy study showed that the acetylation caused a swelling of the kenaf fiber cell wall and that the diameters of isolated nanofibers were between 5 and 50 nm. X-ray analysis showed that the acetylation process reduced the crystallinity of the fibers, whereas mechanical isolation increased it. The method used provides a novel processing route for producing cellulose nanofibers with hydrophobic surfaces.

In the present study, chemical-physical properties of nanofibers isolated from rubberwood (Hevea brasiliensis) and empty fruit bunches (EFB) of oil palm (Elaeis guineensis) were analyzed by microscopic, spectroscopic, thermal and X-ray diffraction methods. The isolation was achieved using chemo-mechanical processes. Microscopy study showed that the diameters of the nanofibers isolated from the EFB ranged from 5 to 40 nm while those of the nanofibers isolated from rubberwood had a wider range (10-90 nm). Fourier transform infrared spectroscopy study demonstrated that almost all the lignin and most of the hemicellulose were removed during the chemical treatments. X-ray diffraction analysis revealed that the crystallinity of the studied nanofibers increased after the chemo-mechanical isolation process. The results of thermogravimetric analysis showed that the nanofibers isolated from both sources had higher thermal stability than those of the bleached pulp and untreated fibers

The main goal of this article is to provide an overview of recent research in the area of cellulose nanomaterial production from different sources. Due to their abundance, renewability, high strength and stiffness, eco-friendliness and low weight, numerous studies have been reported on the isolation of cellulose nanomaterials from different cellulosic sources and their use in high-performance applications. This report covers an introduction to the definition of nanocellulose as well as the methods used for isolation of nanomaterials (including nanocrystals and nanofibers, CNCs and CNFs, respectively) from various sources. The web-like network structure (CNFs) can be extracted from natural sources using mechanical processes, which include high-pressure homogenization, grinding and refining treatments. Also, rod-like CNCs can be isolated from sources such as wood, plant fibers, agricultural and industrial bioresidues, tunicates and bacterial cellulose using an acid hydrolysis process. Following this, the article focuses on the characterization methods, material properties and structures. Encyclopedic characteristics of CNFs and CNCs obtained from different source materials and/or studies are also included. The current report is a comprehensive review of the literature regarding nanocellulose isolation and demonstrates the potential of cellulose nanomaterials for a wide range of high-tech applications.

Cellulose nanofibre coatings were treated by a dielectric barrier discharge plasma in a He/NH3 gas mixture at atmospheric pressure. Ultrasound was optionally irradiated during the treatment. The treatment enhanced the wetting of deionized water, glycerol, and uncured epoxy. Irradiation of ultrasound did not significantly change optical emission from the plasma, but increased the oxygen contents and enhanced etching and roughening at the nanofibre coating surfaces. Furthermore, the irradiation of ultrasound enhanced the wetting of deionized water and glycerol drastically, while that of uncured epoxy to some extent.

The study explores the potential of cellulose nanocrystals (CNC), cellulose nanofibers (CNF) and chitin nanocrystals (ChNC) isolated from bioresidues to remove silver ions from contaminated water. Zeta sizer studies showed negatively charged surfaces for CNC and CNF isolated from cellulose sludge in the acidic and alkaline pHs, whereas ChNC isolated from crab shell residue showed either positive or negative charges depending on pH conditions. Model water containing silver ions showed a decrease in Ag+ ion concentration (measured by inductively coupled plasma-optical emission spectrometer; inductively coupled plasma mass spectrometry), after treatment with CNC, CNF and ChNC suspensions. The highest Ag+ ion removal was measured near neutral pH for CNC, being 34.4 mg/g, corresponding to 64 % removal. ChNC showed 37 % and CNF showed 27 % removal of silver ions. The WDX (wavelength dispersive X-ray analysis) and XPS (X-ray photoelectron spectroscopy) analysis confirmed the presence of silver ions on the surface of the nanocellulose and nanochitin after adsorption. Surface adsorption on the nanoparticles via electrostatic interactions is considered to be the prominent mechanism of heavy metal ion capture from aqueous medium, with CNC with negative surface charge and negatively charged functional groups being most favourable for the adsorption of positively charged Ag+ ions compared to other native bionanomaterials

Suspensions of commercial refined beech pulp (RBP) were further processed through mechanical disintegration (MD-RBP), chemical modification (CM-RBP) and through chemical modification followed by mechanical disintegration (CM-MD-RBP). Nanocomposites were prepared by compounding a poly(vinyl acetate) (PVAc) latex adhesive with increasing contents of the different types of nanofibrils, and the resulting nanocomposites were analyzed by dynamic mechanical analysis (DMA). Also, the suitability of using the CM-RBP fibrils to formulate PVAc adhesives for wood bonded assemblies with improved heat resistance was studied. The presence of cellulose nanofibrils had a strong influence on the viscoelastic properties of PVAc latex films. For all nanocomposites, increasing amounts of cellulose nanofibrils (treated or untreated) led to increasing reinforcing effects in the glassy state, but especially in the PVAc and PVOH glass transitions. This reinforcement primarily resulted from interactions between the cellulose fibrils network and the hydrophilic PVOH matrix that led to the complete disappearance of the PVOH glass transition (tan δ peak) for some fibril types and contents. At any given concentration in the PVOH transition, the CM-MD-RBP nanofibrils provided the highest reinforcement, followed by the MD-RBP, CM-RBP and the untreated RBP. Finally, the use of the CM-RBP fibrils to prepare PVAc reinforced adhesives for wood bonding was promising since, even though they generally performed worse in dry and wet conditions, the boards showed superior heat resistance (EN 14257) and passed the test for durability class D1.

Collagen and cellulose nanofiber based composites were prepared by solution casting followed by pH induced in situ partial fibrillation of collagen phase and crosslinking of collagen phase using gluteraldehyde. Microscopy studies on the materials confirmed the presence of fibrous collagen and cellulose nanofibers embedded in the collagen matrix. The cellulose nanofiber addition as well as collagen crosslinking showed significant positive impact on the nanocomposite's mechanical behaviour. The synergistic performance of the nanocomposites indicated stabilization and reinforcement through strong physical entanglement between collagen and cellulose fibres as well as chemical interaction between collagen matrix and collagen fibrils. The mechanical performance and stability in moist conditions showed the potential of these materials as implantable scaffolds in biomedical applications. The collagen-cellulose ratio, crosslinking agent and crosslinking level of collagen may be further optimised to tailor the mechanical properties and cytocompatibility of these composites for specific applications such as artificial ligament or tendon

Nanocellulose papers offer high tensile strength and modulus but suffer from drawbacks such as their brittle nature. We show that mercerisation of cellulose nanopapers in strong alkaline media for 2 min to 24 h results in the (partial) transformation of native cellulose I into the more ductile cellulose II allomorph. The strain to failure of mercerised nanopapers tripled compared to the original nanopapers while retaining their tensile strength in excess of 100 MPa at the expense of a slight drop in modulus resulting in a significant increase in toughness (total work of fracture). An additional advantage of mercerisation is a reduction in porosity of the nanopapers and increased transparency.

Spruce galactoglucomannans (GGM) and konjac glucomannan (KGM) were mixed with cellulose nanowhiskers (CNW) to form composite films. Remarkable effects of CNW on the appearance of the films were detected when viewed with regular and polarizing optical microscopes and with a scanning electron microscope. Addition of CNW to KGM-based films induced the formation of fiberlike structures with lengths of several millimeters. In GGM-based films, rodlike structures with lengths of several tens of micrometers were formed. The degree of crystallinity of mannan in the plasticized KGM-based films increased slightly when CNW were added, from 25 to 30%. The tensile strength of the KGM-based films not containing glycerol increased with increasing CNW content from 57 to 74 MPa, but that of glycerol-plasticized KGM and GGM films was not affected. Interestingly, the notable differences in the film structure did not appear to be related to the thermal properties of the films

The rheological properties of aqueous suspensions based on three different nanocelluloses were compared. One system was obtained via acid hydrolysis (thus yielding crystalline nanocellulose, CNC) and the other two from mechanical shearing, but from different origins and subjected to different pretreatments. Of the latter two, one was considered to be a rather typical cellulose nanofibril (CNF) suspension whereas the other was a kind of intermediate between CNF and CNC. All three nanocellulose elements differed in dimensions as evident from transmission electron microscopy and atomic force microscopy. With regard to the length of the fibrils/particles, the three nanocelluloses formed three distinct groups with lengths between 200 and slightly more than 800 nm. The three cellulosic elements were also subjected to a TEMPO-mediated oxidation yielding a similar carboxylate content in the three systems. Furthermore, the TEMPO-oxidized elements were grafted with poly(ethylene glycol) (PEG). The amount of grafted PEG was about 35 wt%. The shear viscosity, the storage modulus and the loss modulus of suspensions of the unmodified, the TEMPO-oxidized and the grafted nanocelluloses were determined at room temperature and the solids content of the suspensions was varied between 0.7 and 2.0 wt%. It was concluded that the rheological properties varied significantly between the suspensions depending on the dimensions of the cellulosic elements and their surface characteristics. In this context, the length (or the aspect ratio) of the particles played a very important role.

Randomly oriented fiber mats of chitosan-polyethylene oxide matrix reinforced with cellulose nanocrystals (CNCs) were prepared by electrospinning technique. The cellulose nanocrystals used were isolated using hydrochloric acid (CNCHCl) or sulphuric acid (CNCH2SO4) and the CNCs concentration was 50 wt% in the electrospun mats. The surface characteristics of the nanocrystals were found to affect the dispersion, viscosity, conductivity and zeta-potential of the respective spinning solutions and resulted in better spinnability, homogeneity as well as crosslinking of CNCHCl based nanocomposite fiber mats compared to CNCH2SO4 ones. The microscopy studies showed that diameter of the electrospun fibers decreased by the inclusion of both types of nanocrystals and the crosslinking decreased the porosity of the mats. The tensile strength and tensile modulus of the mats increased with the addition of nanocrystals and increased further for the CNCHCl based mats (58 MPa, 3.1 GPa) after crosslinking. The as-spun CNCHCl based mats had average pore diameters of 1.6 μm and porosity of 38%. The water vapor permeability and the O2/CO2 transmission increased with the addition of CNCHCl. The used nanocrystals as well as electrospun mats showed non-cytotoxic impact towards adipose derived stem cells (ASCs) was considered favorable for wound dressing.

A quantitative analysis of degree of transformation from a softwood sulphite dissolving pulp to alkalised material and the yield of this transformation as a function of the simultaneous variation of the NaOH concentration, denoted [NaOH], reaction time and temperature was performed. Samples were analysed with Raman spectroscopy in combination with multivariate data analysis and these results were confirmed by X-ray diffraction. Gravimetry was used to measure the yield. The resulting data were related to the processing conditions in a Partial Least Square regression model, which made it possible to explore the relevance of the three studied variables on the responses. The detailed predictions for the interactive effects of the measured parameters made it possible to determine optimal conditions for both yield and degree of transformation in viscose manufacturing. The yield was positively correlated to the temperature from room temperature up to 45 °C, after which the relation was negative. Temperature was found to be important for the degree of transformation and yield. The time to reach a certain degree of transformation (i.e. mercerisation) depended on both temperature and [NaOH]. At low temperatures and high [NaOH], mercerisation was instantaneous. It was concluded that the size of fibre particles (mesh range 0.25–1 mm) had no influence on degree of transformation in viscose processing conditions, apparently due to the quick reaction with the excess of NaOH.

Biobased nanofibers are increasingly considered in purification technologies due to their high mechanical properties, high specific surface area, versatile surface chemistry and natural abundance. In this work, cellulose and chitin nanofibers functionalized with carboxylate entities have been prepared from pulp residue (i.e., a waste product from the pulp and paper production) and crab shells, respectively, by chemically modifying the initial raw materials with the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated oxidation reaction followed by mechanical disintegration. A thorough investigation has first been carried out in order to evaluate the copper(II) adsorption capacity of the oxidized nanofibers. UV spectrophotometry, X-ray photoelectron spectroscopy and wavelength dispersive X-rays analysis have been employed as characterization tools for this purpose. Pristine nanofibers presented a relatively low content of negative charges on their surface thus adsorbing a low amount of copper(II). The copper adsorption capacity of the nanofibers was enhanced due to the oxidation treatment since the carboxylate groups introduced on the nanofibers surface constituted negative sites for electrostatic attraction of copper ions (Cu2+). The increase in copper adsorption on the nanofibers correlated both with the pH and carboxylate content and reached maximum values of 135 and 55 mg g−1 for highly oxidized cellulose and chitin nanofibers, respectively. Furthermore, the metal ions could be easily removed from the contaminated nanofibers through a washing procedure in acidic water. Finally, the adsorption capacity of oxidized cellulose nanofibers for other metal ions, such as nickel(II), chromium(III) and zinc(II), was also demonstrated. We conclude that TEMPO oxidized biobased nanofibers from waste resources represent an inexpensive and efficient alternative to classical sorbents for heavy metal ions removal from contaminated water.

The current work reports a novel, completely water based approach to prepare the water resistant modified cellulose nanopapers. Lactic acid in aqueous medium was attached on cellulose nanofibers surface with the aid of ultra-sonication and later oligomerized (polymerized) by compression molding under high temperature and pressure, to obtain the modified nanopapers with enhanced mechanical properties. The modified nanopapers showed an increase of 32% in the elastic modulus and 30% in the yield strength over reference nanopapers. Additionally, the modified nanopaper was hydrophobic in nature and had superior storage modulus under moist conditions. The storage modulus of wet modified nanopaper was three times (2.4 GPa) compared to the reference nanopapers (0.8 GPa) after 1 h immersion in water. Finally, the thermal stability of the modified nanopaper was also higher than reference nanopaper. The material reported is 100% bio-based

Poly(vinyl alcohol) (PVA) foams reinforced with cellulose nanocrystals (CNCs) were prepared with formaldehyde as a crosslinking agent. Two initial reaction times (10, 120 s) and the addition of CNCs (0–2 wt% based on total reaction suspension) were found to affect the foam density, water uptake, morphology and mechanical properties. A longer initial reaction time resulted in higher mechanical properties and density, due to the small pore size. The addition of CNCs induced a progressive decrease in the pore diameter and an increase in the foam density, as well as improved mechanical properties. With 1.5 wt% CNC content, the compressive strength of the PVA foams was significantly improved from 7 to 58 kPa for 10 s-initial reaction time and from 65 to 115 kPa for 120 s-initial reaction time. Results showed that the cross-linked PVA foams with CNC had promising properties for use in biomedical applications.

In this work, the defibrillation of cellulose fibers (CF) in the presence of hydroxyethyl cellulose (HEC) within the one-step twin-screw extrusion (TSE) process was examined. The effect of the TSE on cellulose fiber size reduction as well as CF-HEC biocomposites properties were investigated. The results showed that the TSE of cellulose fiber-hydroxyethyl cellulose (CF-HEC) with different cellulose fiber contents (50, 65, and 80 wt%) resulted in partial defibrillation of the cellulose fibers. The fractionation test of the cellulose fibers confirmed that their size was reduced and some fibrillation was observed in microscopy studies. The maximum width reduction of 46% occurred with 80 wt% cellulose content. However, the partial width reduction was also observed with 50% and 65 wt% of cellulose contents. Based on rheological measurements, the shear-viscosity trend of CF-HEC dispersion abruptly dropped when higher fiber content (80 wt%) was extruded, which was related to the fibrillation of the cellulose fibers as well as the reduction of the length. The extruded CF-HEC materials (powder form) were compression molded to prepare the biocomposites with different cellulose fiber contents (50, 65, and 80 wt%). The extruded CF-HEC powders were diluted with addition extra HEC to make biocomposites with lower fiber content (20%, 30%, and 40 wt%) and compression molded to study how the size reduction of the cellulose fibers affected the mechanical properties of biocomposites. The results showed that the E-modulus improved from 0.4 GPa of the neat HEC to 1.6 GPa for the composite with 40 wt% CF. Interestingly, the tensile strength of CF-HEC biocomposite with 40 wt% confirmed a clear improvement from 9.8 to 26.6 MPa, confirming good interaction between HEC and CF. Graphic abstract Preparation (mixing, TSE, and hot-pressing) and characterization (FE-SEM, rheometry, and tensile test) of CF-HEC biocomposite

CO2 adsorption is a promising strategy to reduce costs and energy use for CO2 separation. In this study, we developed CO2 adsorbents based on lightweight and flexible cellulose nanofiber aerogels with monolithic structures prepared via freeze-casting, and cellulose acetate or acetylated cellulose nanocrystals (a-CNCs) were introduced into the aerogels as functional materials using an impregnation method to provide CO2 affinity. The microstructure of the adsorbent was examined using scanning electron microscopy, and compression tests were performed to analyze the mechanical properties of the adsorbents. The CO2 adsorption behavior was studied by recording the adsorption isotherms and performing column breakthrough experiments. The samples showed excellent mechanical performance and had a CO2 adsorption capacity of up to 1.14 mmol/g at 101 kPa and 273 K. Compared to the adsorbent which contains cellulose acetate, the one impregnated with a-CNCs had better CO2 adsorption capacity and axial mechanical properties owing to the building of a nanoscale scaffold on the surface of the adsorbent. Although the CO2 adsorption capacity could be improved further, this paper reports a potential CO2 adsorbent that uses all cellulose-based materials, which is beneficial for the environment from both resource and function perspectives. Moreover, the interesting impregnation process provides a new method to attach functional materials to aerogels, which have potential for use in many other applications.

The relationships between biomass composition, water retention value (WRV), settling volume and enzymatic glucose yield and enzyme binding is investigated in this work by employing grasses pretreated with combinations of alkaline hydrogen peroxide (AHP) delignification and liquid hot water pretreatment that result in significant alterations of cell wall properties and subsequent enzymatic hydrolysis yields. Specifically, these cell wall treatments are performed on corn stover and switchgrass to generate material with a range of lignin (6-35 %) and xylan (2-28 %) contents as well as a range of other properties such as carboxylic acid content, water binding affinity and swellability. It was determined that WRV and settling volume are predictors of glucose yield (R2 = 0.900 and 0.895 respectively) over the range of materials and treatment conditions used. It was also observed that mild AHP delignification can result in threefold increases in the WRV. Dynamic vapor sorption isotherms demonstrated that AHP-delignified corn stover exhibited an increased affinity for water sorption from the vapor phase relative to untreated corn stover. These results indicate that these water properties may be useful proxies for biomass susceptibility to enzymatic deconstruction.

Nuclear magnetic resonance (NMR) relaxometry is applied to provide direct measurement of water adsorption in anatomical fractions of corn stover. NMR transverse T2 relaxation time distribution measurements indicate multiple water populations, which vary with anatomical fraction and water adsorption. Measured T2 data are used to calculate thermodynamic properties of Brunauer-Emmet-Teller adsorption theory using a model to estimate mono and bilayer relaxation. T2 data are used directly to determine rotational diffusion correlation times indicating adsorption interaction strength. T1-T2 longitudinal-transverse relaxation time correlation measurements quantify differences in the molecular level structural order of the adsorbate surface water as a function of water activity, i.e. relative humidity or water vapor partial pressure. The T1/T2 ratio provides a measure of the surface energy related to the adsorption strength and surface diffusive mobility of the water adsorbate and differentiates the anatomical fractions. The results indicate that direct measurement of NMR relaxation times can be used to characterize corn stover biomass water adsorption, data relevant to processing and handling considerations.