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Cellulose nanofibrils (CNFs) have emerged as sustainable options for a wide range of applications. However, the high aspect ratio and biopersistence of CNFs raise concerns about potential health effects. Here, we evaluated the in vivo pulmonary and systemic toxicity of unmodified (U-CNF), carboxymethylated (C-CNF), and TEMPO (2,2,6,6-tetramethyl-piperidin-1-oxyl)-oxidized (T-CNF) CNFs, fibrillated in the same way and administered to mice by repeated (3×) pharyngeal aspiration (14, 28, and 56 μg/mouse/aspiration). Toxic effects were assessed up to 90 days after the last administration. Some mice were treated with T-CNF samples spiked with lipopolysaccharide (LPS; 0.02-50 ng/mouse/aspiration) to assess the role of endotoxin contamination. The CNFs induced an acute inflammatory reaction that subsided within 90 days, except for T-CNF. At 90 days post-administration, an increased DNA damage was observed in bronchoalveolar lavage and hepatic cells after exposure to T-CNF and C-CNF, respectively. Besides, LPS contamination dose-dependently increased the hepatic genotoxic effects of T-CNF.

Natural biopolymers have become key players in the preparation of biodegradable food packaging. However, biopolymers are typically highly hydrophilic, which imposes limitations in terms of barrier properties that are associated with water interactions. Here, we enhance the barrier properties of biobased packaging using multilayer designs, in which each layer displays a complementary barrier function. Oxygen, water vapor, and UV barriers were achieved using a stepwise assembly of cellulose nanofibers, biobased wax, and lignin particles supported by chitin nanofibers. We first engineered several designs containing CNFs and carnauba wax. Among them, we obtained low water vapor permeabilities in an assembly containing three layers, i.e., CNF/wax/CNF, in which wax was present as a continuous layer. We then incorporated a layer of lignin nanoparticles nucleated on chitin nanofibrils (LPChNF) to introduce a complete barrier against UV light, while maintaining film translucency. Our multilayer design which comprised CNF/wax/LPChNF enabled high oxygen (OTR of 3 ± 1 cm 3 /m 2 ·day) and water vapor (WVTR of 6 ± 1 g/m 2 ·day) barriers at 50% relative humidity. It was also effective against oil penetration. Oxygen permeability was controlled by the presence of tight networks of cellulose and chitin nanofibers, while water vapor diffusion through the assembly was regulated by the continuous wax layer. Lastly, we showcased our fully renewable packaging material for preservation of the texture of a commercial cracker (dry food). Our material showed functionality similar to that of the original packaging, which was composed of synthetic polymers.

Current research targets innovative medical textiles of nanofibrous nature and antibacterial activity to prevent diaper dermatitis. The work is based on electrospun nanofibers from cellulose acetate (CA) and lignin (Lig) polymers. A series of new copper complexes were synthesized and loaded to the CA/Lig solution mix then subjected to electrospinning, giving rise to the tricomponent bioactive mats CA/Lig/Cu-complex. The surface morphology of electrospun nanofiber mats was smooth and homogenous as the concentration of lignin increased in the mixture. The incorporation of lignin improved the electrospinnability of the cellulose acetate; however, it increased the fiber diameter. The water contact angle, absorption underload were significantly improved as lignin content increased. The incorporation of Cu-complex in electrospun CA and CA/Lig fiber mats occurred without any substantial change in the surface morphology, indicating well encapsulation of the complex. The electrospun mats were active against Pseudomonas aeruginosa, Acinetobacter baumannii, Staphylococcus epidermidis, and Streptococcus faecalis. The cytotoxicity, protein leakage, and biological results, together with the above studies, would advocate copper complex loaded CA/Lig nanofibers as a potential candidate for hygienic applications., (Copyright © 2022. Published by Elsevier B.V.)

Background: Cellulose nanofibrils (CNFs) have emerged as a sustainable and environmentally friendly option for a broad range of applications. The fibrous nature and high biopersistence of CNFs call for a thorough toxicity assessment, but it is presently unclear which physico-chemical properties could play a role in determining the potential toxic response to CNF. Here, we assessed whether surface composition and size could modulate the genotoxicity of CNFs in human bronchial epithelial BEAS-2B cells. We examined three size fractions (fine, medium and coarse) of four CNFs with different surface chemistry: unmodified (U-CNF) and functionalized with 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO) (T-CNF), carboxymethyl (C-CNF) and epoxypropyltrimethylammonium chloride (EPTMAC) (E-CNF). In addition, the source fibre was also evaluated as a non-nanosized material., Results: The presence of the surface charged groups in the functionalized CNF samples resulted in higher amounts of individual nanofibrils and less aggregation compared with the U-CNF. T-CNF was the most homogenous, in agreement with its high surface group density. However, the colloidal stability of all the CNF samples dropped when dispersed in cell culture medium, especially in the case of T-CNF. CNF was internalized by a minority of BEAS-2B cells. No remarkable cytotoxic effects were induced by any of the cellulosic materials. All cellulosic materials, except the medium fraction of U-CNF, induced a dose-dependent intracellular formation of reactive oxygen species (ROS). The fine fraction of E-CNF, which induced DNA damage (measured by the comet assay) and chromosome damage (measured by the micronucleus assay), and the coarse fraction of C-CNF, which produced chromosome damage, also showed the most effective induction of ROS in their respective size fractions., Conclusions: Surface chemistry and size modulate the in vitro intracellular ROS formation and the induction of genotoxic effects by fibrillated celluloses. One cationic (fine E-CNF) and one anionic (coarse C-CNF) CNF showed primary genotoxic effects, possibly partly through ROS generation. However, the conclusions cannot be generalized to all types of CNFs, as the synthesis process and the dispersion method used for testing affect their physico-chemical properties and, hence, their toxic effects., (© 2022. The Author(s).)

Plant-based hydrogels have attracted great attention in biomedical fields since they are biocompatible and based on natural, sustainable, cost-effective, and widely accessible sources. Here, we introduced new viscoelastic bio-inks composed of quince seed mucilage and cellulose nanofibrils (QSM/CNF) easily extruded into 3D lattice structures through direct ink writing in ambient conditions. The QSM/CNF inks enabled precise control on printing fidelity where CNF endowed objects with shape stability after freeze-drying and with suitable porosity, water uptake capacity, and mechanical strength. The compressive and elastic moduli of samples produced at the highest CNF content were both increased by ~100% (from 5.1 ± 0.2 kPa and 32 ± 1 kPa to 10.7 ± 0.5 and 64 ± 2 kPa, respectively). These values ideally matched those reported for soft tissues; accordingly, the cell compatibility of the printed samples was evaluated against HepG2 cells (human liver cancer). The results confirmed the 3D hydrogels as being non-cytotoxic and suitable to support attachment, survival, and proliferation of the cells. All in all, the newly developed inks allowed sustainable 3D bio-hydrogels fitting the requirements as scaffolds for soft tissue engineering., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

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.

Direct-ink-writing (DIW) of hydrogels has become an attractive research area due to its capability to fabricate intricate, complex, and highly customizable structures at ambient conditions for various applications, including biomedical purposes. In the current study, cellulose nanofibrils reinforced aloe vera bio-hydrogels were utilized to develop 3D geometries through the DIW technique. The hydrogels revealed excellent viscoelastic properties enabled extruding thin filaments through a nozzle with a diameter of 630 μm. Accordingly, the lattice structures were printed precisely with a suitable resolution. The 3D-printed structures demonstrated significant wet stability due to the high aspect ratio of the nano- and microfibrils cellulose, reinforced the hydrogels, and protected the shape from extensive shrinkage upon drying. Furthermore, all printed samples had a porosity higher than 80% and a high-water uptake capacity of up to 46 g/g. Altogether, these fully bio-based, porous, and wet stable 3D structures might have an opportunity in biomedical fields., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Hypothesis: Nanocellulose and nanochitin are both biobased materials with complementary structures and properties. Both exhibit pH-dependent surface charges which are opposite in sign. Hence, it should be possible to manipulate them to form complexed structures via ionic bond formation at prescribed pH conditions., Experiment: Nanocellulose and nanochitin were mixed after exposure to acidic or neutral conditions to influence their ionization state. The heat of interaction during the introduction of nanochitin to nanocellulose was monitored via isothermal titration calorimetry. The strength and gel properties of the resulting structures were characterized via rheological measurement., Findings: The resultant gel properties in the designed hybrid systems were found to depend directly on the charge state of the starting materials, which was dictated by pH adjustment. Different interparticle interactions including ionic attraction, hydrophobic associations, and physical entanglement were identified in the systems and the influence of each was elucidated for different conditions of pH, concentration, and ratio of nanochitin to nanocellulose. Hydrophobic associations between neutralized nanochitin particles were found to contribute strongly to increased elastic modulus values. Ionic complex formation was found to provide enhanced stability under broader pH conditions, while physical entanglement of cellulose nanofibers was a substantial thickening mechanism in all systems., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

We use acetylated cellulose nanofibrils (AcCNF) to stabilize transient emulsions with paraffin that becomes shape-stable and encapsulated phase change material (PCM) upon cooling. Rheology measurements confirm the gel behavior and colloidal stability of the solid suspensions. We study the effect of nanofiber content on PCM leakage upon melting and compare the results to those from unmodified CNF. The nanostructured cellulose promotes paraffin phase transition, which improves the efficiency of thermal energy exchange. The leakage-proof microcapsules display high energy absorption capacity (ΔH m  = 173 J/g) at high PCM loading (up to 80 wt%), while effectively controlling the extent of supercooling. An excellent thermal stability is observed during at least 100 heating/cooling cycles. Degradation takes place at 291 °C, indicating good thermal stability. The high energy density and the effective shape and thermal stabilization of the AcCNF-encapsulated paraffin points to a sustainable solution for thermal energy storage and conversion., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cellulose (CNF) and chitin (ChNF) nanofibers are known to form materials that are both tough and strong. In this study, we hypothesize that the inertness of networks produced from CNF and ChNF makes them ideal templates for heterogeneous reactions and in situ formation of nanoarchitectures. We expand nanoparticle templating on polysaccharide colloids by introducing a new and facile process that leads to the growth of organic nanoparticles on CNF and ChNF in aqueous media. The process, based on solvent shifting supported on solid interfaces, is demonstrated by direct observation of lignin nanoparticles that are further used for their photocatalytic activity. Importantly, the dynamics of nanoparticle nucleation and growth is correlated with the surface chemistry of the templating nanopolysaccharides. Electrostatic repulsion between the deprotonated lignin molecules and the slightly negative CNF support led to limited adsorption and was effective in producing free (nonbound) lignin nanoparticles (28 ± 7 nm) via precipitation. In contrast, the stronger interfacial interactions between the positively charged ChNF and lignin molecules facilitated instantaneous and extensive lignin adsorption, followed by nucleation and growth into relatively larger nanoparticles (46 ± 17 nm). The latter were homogeneously distributed and strongly coupled to the ChNF support. Overall, we introduce lignin nanoparticle nucleation and growth on renewable nanopolysaccharides, offering an effective route toward in situ synthesis of highly functional fibrils and related cohesive films that offer a great potential in packaging and other applications.

We introduce a green and facile method to compatibilize hydrophobic polylactide (PLA) with hydrophilic cellulose nanofibers (CNF) by using ionic liquid ([DBNH][OAc]) welding with a cosolvent system (gamma-valerolactone). Such welding affords strong (230 MPa tensile strength), flexible (13% elongation at break), transparent (>90%) and defect-free CNF/PLA films. The films are biodegradable in marine environments (70% degradation in 7 weeks), facilitating the otherwise slow PLA decomposition. Physical, chemical and structural features of the films before and after welding are compared and factored in the trends observed for degradation in seawater. The results point to the possibility of PLA-based films forming a co-continuous system with nanocellulose to achieve an improved performance. The role of film morphology, hydrophobicity, and crystallinity is discussed to add to the prospects for packaging materials that simultaneously display accelerated degradability in marine environments., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

The rheological behavior of aqueous suspensions of lignocellulose nanofibrils (LCNFs) is investigated systematically by considering the coupled effect of residual lignin and LCNF morphology. The LCNF was obtained by high-energy fluidization of TEMPO-oxidized mechanical fibers, followed by size fractionation (fibril widths of ∼5, ∼9, and ∼18 nm). The nanofibril width and the corresponding fibril-fibril interactions are strongly influenced by the presence and distribution of lignin in the respective fractions, either retained on the fibril surface or as free structures present in the finest size fraction. All samples containing lignin display dilatancy, typifying gel suspensions with aggregated hydrophobic particles. Fine fractionated samples display strong gel behavior. The coarse fractionated sample, by contrast, shows a greater tendency to flocculate via entanglement and displays less gel-like characteristics; hence, it dewaters more freely.

Hydrogels of TEMPO-oxidized nanocellulose were stabilized for dry-jet wet spinning using a shell of cellulose dissolved in 1,5-diazabicyclo[4.3.0]non-5-enium propionate ([DBNH][CO 2 Et]), a protic ionic liquid (PIL). Coagulation in an acidic water bath resulted in continuous core-shell filaments (CSFs) that were tough and flexible with an average dry (and wet) toughness of ∼11 (2) MJ·m -3 and elongation of ∼9 (14) %. The CSF morphology, chemical composition, thermal stability, crystallinity, and bacterial activity were assessed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, liquid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, pyrolysis gas chromatography-mass spectrometry, wide-angle X-ray scattering, and bacterial cell culturing, respectively. The coaxial wet spinning yields PIL-free systems carrying on the surface the cellulose II polymorph, which not only enhances the toughness of the filaments but facilities their functionalization.

We study the generation and decay of aqueous foams stabilized by sodium dodecyl sulfate (SDS) in the presence of unmodified cellulose nanofibrils (CNF). Together with the rheology of aqueous suspensions containing CNF and SDS, the interfacial/colloidal interactions are determined by quartz crystal microgravimetry with dissipation monitoring, surface plasmon resonance, and isothermal titration calorimetry. The results are used to explain the properties of the air/water interface (interfacial activity and dilatational moduli determined from oscillating air bubbles) and of the bulk (steady-state flow, oscillatory shear, and capillary thinning). These properties are finally correlated to the foamability and to the foam stability. The latter was studied as a function of time by monitoring the foam volume, the liquid fraction, and the bubble size distribution. The shear-thinning effect of CNF is found to facilitate foam formation at SDS concentrations above the critical micelle concentration ( c SDS ≥ cmc ). Compared with foams stabilized by pure SDS, the presence of CNF enhances the viscosity and elasticity of the continuous phase as well as of the air/water interface. The CNF-containing foams have higher liquid fractions, larger initial bubble sizes, and better stability. Due to charge screening effects caused by sodium counter ions and depletion attraction caused by SDS micelles, especially at high SDS concentrations, CNF forms aggregates in the Plateau borders and nodes of the foam, thus slowing down liquid drainage and bubble growth and improving foam stability. Overall, our findings advance the understanding of the role of CNF in foam generation and stabilization.

A major challenge exists in the preparation of scaffolds for bone regeneration, namely, achieving simultaneously bioactivity, biocompatibility, mechanical performance and simple manufacturing. Here, cellulose nanofibrils (CNF) are introduced for the preparation of scaffolds taking advantage of their biocompatibility and ability to form strong 3D porous networks from aqueous suspensions. CNF are made bioactive for bone formation through a simple and scalable strategy that achieves highly interconnected 3D networks. The resultant materials optimally combine morphological and mechanical features and facilitate hydroxyapatite formation while releasing essential ions for in vivo bone repair. The porosity and roughness of the scaffolds favor several cell functions while the ions act in the expression of genes associated with cell differentiation. Ion release is found critical to enhance the production of the bone morphogenetic protein 2 (BMP-2) from cells within the fractured area, thus accelerating the in vivo bone repair. Systemic biocompatibility indicates no negative effects on vital organs such as the liver and kidneys. The results pave the way towards a facile preparation of advanced, high performance CNF-based scaffolds for bone tissue engineering.

Mechanically fibrillated cellulose nanofibrils (CNFs) have attracted special attention as building blocks for the development of advanced materials and composites. A correlation exists between CNF morphology and the properties of the materials they form. However, this correlation is often evaluated indirectly by process-centered approaches or by accessing a single dimensionality of CNFs adsorbed on solid supports. High-resolution imaging is currently the best approach to describe the morphological features of nanocelluloses; nevertheless, adsorption effects need to be accounted for. For instance, possible deformations of the CNFs arising from capillary forces and interactions with the substrate need to be considered in the determination of their cross-sectional dimensions. By considering soft matter imaging and adsorption effects, we provide evidence of the deformation of CNFs upon casting and drying. We determine a substantial flattening associated with the affinity of CNFs with the substrate corresponding to a highly anisotropic cross-sectional geometry (ellipsoidal) in the dried state. Negative-contrast scanning electron microscopy is also introduced as a new method to assess the dimensions of the CNFs. The images obtained by the latter, a faster imaging method, were correlated with those from atomic force microscopy. The cross-sectional area of the CNF is reconstructed by cross-correlating the widths and heights obtained by the two techniques.

Multiphase (emulsion) gels with internal phase fractions between 0.1 and 0.5 were formulated at low loadings of cellulose nanofibrils (CNF), alginate, and polylactide (PLA). Their properties (rheology and morphology) fitted those of inks used for direct ink writing (DIW). The effect of formulation and composition variables were elucidated after printing cubic scaffolds and other solid designs. The distinctive microstructures that were developed allowed high printing fidelity and displayed limited shrinkage after room temperature and freeze-drying (0 and 5% shrinkage in the out-of-plane and in-plane directions upon freeze-drying, respectively). The CNF added in the continuous phase was shown to be critical to achieve rheology control as an effective interfacial stabilizer and to ensure the printability of the ink toward high structural reliability. We found that the extent of shape retention of the dried scaffolds resulted from the tightly locked internal structure. The PLA that was initially added in the nonpolar or organic phase (0 to 12%) was randomly embedded in the entire scaffold, providing a strong resistance to shrinkage during the slow water evaporation at ambient temperature. No surface collapse or lateral deformation of the dried scaffolds occurred, indicating that the incorporation of PLA limited drying-induced shape failure. It also reduced compression strain by providing better CNF skeletal support, improving the mechanical strength. Upon rewetting, the combination of the hydrophilicity imparted by CNF and alginate together with the highly porous structure of the 3D material and the internal microchannels contributed to high water absorption via capillary and other phenomena (swelling % between ∼400 and 900%). However, no shape changes occurred compared to the initial 3D-printed shape. The swelling of the scaffolds correlated inversely with the PLA content in the precursor emulsion gel, providing a means to regulate the interaction with water given its low surface energy. Overall, the results demonstrate that by compatibilization of the CNF-based hydrophilic and the PLA-based hydrophobic components, it is possible to achieve shape control and retention upon 3D printing, opening the possibility of adopting low-solids inks for DIW into dry objects. The dryable CNF-based 3D structural materials absorb water while being able to support load (high elastic modulus) and maintain the shape upon hydration.

Two-dimensional (hydrophilic) channels were patterned on films prepared from cellulose nanofibrils (CNF) using photolithography and inkjet printing. Such processes included UV-activated thiol-yne click coupling and inkjet-printed designs with polystyrene. The microfluidic channels were characterized (SEM, wetting, and fluid flow) and applied as platforms for biosensing. Compared to results from the click method, a better feature fidelity and flow properties were achieved with the simpler inkjet-printed channels. Human immunoglobulin G (hIgG) was used as target protein after surface modification with either bovine serum albumin (BSA), fibrinogen, or block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) (PDMAEMA- block-POEGMA copolymers). Surface plasmon resonance (SPR) and AFM imaging were used to determine their antifouling effect to prevent nonspecific hIgG binding. Confocal laser scanning microscopy revealed diffusion and adsorption traces in the channels. The results confirm an effective surface passivation of the microfluidic channels (95% reduction of hIgG adsorption and binding). The inexpensive and disposable systems proposed here allow designs with space-resolved blocking efficiency that offer a great potential in biosensing.

Cellulose nanofiber films (CNFF) were treated via a welding process using ionic liquids (ILs). Acid-base-conjugated ILs derived from 1,5-diazabicyclo[4.3.0]non-5-ene [DBN] and 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) were utilized. The removal efficiency of ILs from welded CNFF was assessed using liquid-state nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The mechanical and physical properties of CNFF indicated surface plasticization of CNFF, which improved transparency. Upon treatment, the average CNFF toughness increased by 27%, and the films reached a Young's modulus of ∼5.8 GPa. These first attempts for IL "welding" show promise to tune the surfaces of biobased films, expanding the scope of properties for the production of new biobased materials in a green chemistry context. The results of this work are highly relevant to the fabrication of CNFFs using ionic liquids and related solvents.

Heterogeneous acetylation of wood fibers is proposed for weakening their interfibrillar hydrogen bonding, which facilitates their processing into micro- and nanocelluloses that can be further used to synthesize filaments via wet-spinning. The structural (SEM, WAXD), molecular (SEC), and chemical (FTIR, titration) properties of the system are used to propose the associated reaction mechanism. Unlike the homogeneous acetylation, this method does not alter the main morphological features of cellulose fibrils. Thus, we show for the first time, the exploitation of synergies of compositions simultaneously comprising dissolved cellulose esters and suspended cellulose micro- and nanofibrils. Such colloidal suspension forms a co-continuous assembly with a matrix that interacts strongly with the micro- and nanofibrils in the dispersed phase. This facilitates uninterrupted and defect-free wet-spinning. Upon contact with an antisolvent (water), filaments are easily formed and display a set of properties that set them apart from those reported so far for nanocelluloses: a remarkable stretchability (30% strain) and ultrahigh toughness (33 MJ/m 3 ), both surpassing the values of all reported nanocellulose-based filaments. All the while, they also exhibit competitive stiffness and strength (6 GPa and 143 MPa, respectively). Most remarkably, they retain 90% of these properties after long-term immersion in water, solving the main challenge of the lack of wet strength that is otherwise observed for filaments synthesized from nanocelluloses.

This work investigates multifunctional composite films synthesized with cellulose nanofibers (CNFs) and poly(vinyl alcohol) (PVA). First, TEMPO-oxidized CNFs were modified in the heterogeneous phase with benzophenone, diisocyanate, and epoxidized soybean oil via esterification reactions. A thorough characterization was carried out via elemental analysis as well as FT-IR and X-ray photoelectron spectroscopies and solid-state NMR. Following, the surface-modified CNFs were combined with PVA to endow composite films with UV-absorbing capabilities while increasing their thermomechanical strength and maintaining a high light transmittance. Compared to neat PVF films, the tensile strength, Young modulus, and elongation of the films underwent dramatic increases upon addition of the reinforcing phase (maximum values of ∼96 MPa, ∼ 714 MPa, and ∼350%, respectively). A high UV blocking performance, especially in the UVB region, was observed for the introduced multifunctional PVA films at CNF loadings below 5 wt %. The trade-off between modified nanofibril function as interfacial reinforcement and aggregation leads to an optimum loading. The results indicate promising applications, for example, in active packaging.

Cellulose nanofibrils (CNF) offer great prospects as a natural stabilizer of colloidal dispersions and complex fluids for application in food, pharma, and cosmetics. In this study, an ionic surfactant (sodium dodecyl sulfate, SDS) was used as emulsifier of oil-in-water and water-in-oil emulsions that were further costabilized by addition of CNF. The adsorption properties of SDS in both, CNF dispersions and emulsions, as well as the influence of composition (CNF and SDS concentration) and formulation (ionic strength, oil, and CNF types) on the phase behavior were elucidated and described in the framework of Windsor systems. At low salinity, the phase transition of emulsions containing CNF and SDS at low concentrations was controlled by molecular transfer in the oil-in-water system. Irregular droplets and "bi-continuous" morphologies were observed at medium and high salinity for systems containing high CNF and SDS concentrations. Water-in-oil emulsions were only possible at high salinity and SDS concentrations in the presence of small amounts of CNF. The results revealed some subtle differences in CNF interfacial activity, depending on the method used for their isolation via fiber deconstruction, either from microfluidization or aqueous counter collision. Overall, we propose that the control of emulsion morphology and stability by addition of CNF opens the possibility of developing environmentally friendly complex systems that display high stability and respond to ionic strength following the expectations of classical emulsion systems.

Chitosan (CS), cellulose nanofibrils (CNF) and boric acid, the latter of which was used as flame retardant, were combined in transparent, hybrid films that were produced by solvent casting. The flammability and the thermal stability of the films were studied with respect to the loading of the inorganic component. Chitosan films displayed fire retardancy properties, which were enhanced in the presence of boric acid. CNF films, in contrast to those from chitosan, were readily flammable; however, when combined with boric acid (30w%), they became self-extinguishing. Most remarkably, bicomponent films comprising CNF and chitosan, displayed better fire retardancy than that of neat CS films. Moreover, boric acid improved the thermal stability of the bicomponent films. The tensile strength and Young's modulus of CS, CNF and CS-CNF films improved at intermediate boric acid addition, although a negative effect on elongation was observed., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

We demonstrate benzophenone (BP) conjugation via amine-reactive esters onto oxidized cellulosic fibers that were used as precursors, after microfluidization, of photoactive cellulose nanofibrils (CNF). From these fibrils, cellulose I filaments were synthesized by hydrogel spinning in an antisolvent followed by fast biradical UV cross-linking. As a result, the wet BP-CNF filaments retained extensively the original dry strength (a remarkable ∼80% retention). Thus, the principal limitation of these emerging materials was overcome (the wet tensile strength is typically <0.5% of the value measured in dry conditions). Subsequently, antihuman hemoglobin (anti-Hb) antibodies were conjugated onto residual surface carboxyl groups, making the filaments bifunctional for their active groups and properties (wet strength and bioactivity). Optical (surface plasmon resonance) and electroacoustic (quartz crystal microgravimetry) measurements conducted with the bifunctional CNF indicated effective anti-Hb conjugation (2.4 mg m -2 ), endowing an excellent sensitivity toward Hb targets (1.7 ± 0.12 mg m -2 ) and negligible nonspecific binding. Thus, the anti-Hb biointerface was deployed on filaments that captured Hb efficiently from aqueous matrices (confocal laser microscopy of FITC-labeled antibodies). Significantly, the anti-Hb biointerface was suitable for regeneration, while its sensitivity and selectivity in affinity binding can be tailored by application of blocking copolymers. The developed bifunctional filaments based on nanocellulose offer great promise in detection and affinity binding built upon 1D systems, which can be engineered into other structures for rational use of material and space.

The state of dispersion and the interactions between a polymer and a filler in a nanocomposite crucially define its properties and performance. The affinity of polylactide (PLA) with vegetable and animal proteins (casein, gelatin, soy protein isolate, and hydrolysate) is investigated and their role as eco-friendly dispersants and compatibilizers of cellulose nanofibrils (CNF) is elucidated. The affinity of the proteins with PLA is determined by using sensograms acquired by electroacoustic (quartz crystal microgravimetry) and optical (surface plasmon resonance) techniques. The surface energy of PLA increases upon protein adsorption while the opposite effect is observed for CNF, under identical experimental conditions. A significant improvement in the thermodynamic work of adhesion for PLA/CNF systems is predicted by application of the denatured proteins at low concentrations (∼20% and ∼15% enhancement with soy protein and casein at pH 3 and pH 8, respectively). We offer a robust method to screen denatured proteins and to tailor the wettability and material compatibility in the synthesis of bionanocomposites based on CNF and PLA.

C-reactive protein (CRP) is an acute phase protein that has been widely used as a predictor of cardiovascular diseases. We report herein the synthesis of immunosensors based on carboxylated cellulose nanofibrils (CNF) for CRP detection, as demonstrated by quartz crystal microgravimetry (QCM). QCM sensors carrying ultrathin films of carboxylated CNF were prepared by using two protocols: (i) spin coating of CNF on the sensors followed by carboxylation via in situ oxidation with 2,2,6,6-tetramethylpiperidine 1-oxyl and (ii) carboxymethylation of CNF in aqueous dispersion followed by spin coating deposition on the sensors. Protein A was conjugated to the carboxylated CNF via N-(3-(Dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide and used as a ligand for oriented immobilization of anti C-reactive protein (anti-CRP). The different carboxyl group density of the two oxidized CNF surfaces influenced Protein A binding and, subsequently, the available immobilized anti-CRP molecules. The detection efficiency for CRP, specificity, and concentration range displayed by the carboxylated CNF-based immunosensors coupled with oriented and unoriented anti-CRP were determined and compared.

Two chitosan derivatives, namely, thiol-chitosan (TCs) and chitosan iodoacetamide (CsIA) were newly synthesized by reacting Cs with thiglycolic acid (TGA) and iodoacetic acid (IA) respectively. After being crosslinked with glutraldehyde (GA), the two derivatives were submitted to FT-IR and H 1 NMR analysis for identification and characterization of their chemical features. As TCs and CsIA are water soluble, their electrospun nanofibres mats from aqueous solutions could be crosslinked and achieved using polyvinyl alcohol/Chitosan blend (PVA/Cs) polymers. Morphological structures of the obtained nanofibres and their webs were studied via those of TCs and CsIA free systems. The data also indicate that the crosslinked PVA/Cs/CsIA is more thermally stable than the crosslinked PVA/Cs/TCs and crosslinked PVA/Cs respectively. It was proved that the electrospun fibers containing TCs or CsIA display a superior antibacterial activity against negative bacteria E. Coli with a minimum inhibitory concentration (MIC) of 400μg/ml. These effects are rather in confirmation with bacterial kinetics essays which were also carried out in current work. Of particular interest is that the antimicrobial properties of fibers containing small concentration of either TCs or CsIA are much superior than those obtained with neat Cs electrospun nanofibres used as reference. By and large the results advocate the fibers webs containing TCs or CsIA as excellent candidates for wound dressing applications., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Curdlan (CURD) and polyethylene oxide were used to synthesize nanofibers as carriers of hydro soluble tetracycline hydrochloride (TCH). The viscosity, surface tension and conductivity of the precursor multicomponent aqueous solutions were determined and adjusted to produce defect-free fiber webs. Except for a slight increase in diameter, the addition of TCH did not affect the original morphology of the CURD/PEO nanofibers, as determined by FE-SEM imaging. However, the thermal stability of the system was enhanced (TGA and DSC). Moreover, water resistance, as measured with 24-h immersion tests, was observed upon crosslinking with glutaraldehyde. In-vitro activity measurements indicated a sustained and controlled TCH time-release pattern and excellent antibacterial activity against E. coli, as assessed by UV-vis spectroscopy and viable cell counting, respectively. Overall, we propose nanofibers based on CURD as promising platforms for scaffolds for wound dressing and drug delivery., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A route for the compatibilization of aqueous dispersions of cellulose nanofibrils (CNFs) with a non-polar polymer matrix is proposed to overcome a major challenge in CNF-based material synthesis. Non-ionic surfactants were used in CNF aqueous dispersions equilibrated with an organic phase (for demonstration, a polystyrene solution, PS, was used). Stable water-in-oil-in-water (W/O/W) double emulsions were produced as a result of the compromise between composition and formulation variables. Most remarkably, the proposed route for CNF integration with hydrophobic polymers removed the need for drying or solvent-exchange of the CNF aqueous dispersion prior to processing. The rheological behavior of the double emulsions showed strong shear thinning behavior and facilitated CNF-PS co-mixing in solid nanofibers upon electrospinning. The morphology and thermal properties of the resultant nanofibers revealed that CNFs were efficiently integrated in the hydrophobic matrix which was consistent with the high interfacial area of the precursor double emulsion. In addition, the morphology and quality of the composite nanofibers can be controlled by the conductivity (ionic strength) of the CNF dispersion. Overall, double emulsion systems are proposed as a novel, efficient and scalable platform for CNF co-processing with non-polar systems and they open up the possibility for the redispersion of CNFs after removal of the organic phase.

We passivated TEMPO-oxidized cellulose nanofibrils (TOCNF) toward human immunoglobulin G (hIgG) by modification with block and random copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA). The block copolymers reversibly adsorbed on TOCNF and were highly effective in preventing nonspecific interactions with hIgG, especially if short PDMAEMA blocks were used. In such cases, total protein rejection was achieved. This is in contrast to typical blocking agents, which performed poorly. When an anti-human IgG biointerface was installed onto the passivated TOCNF, remarkably high affinity antibody-antigen interactions were observed (0.90 ± 0.09 mg/m(2)). This is in contrast to the nonpassivated biointerface, which resulted in a significant false response. In addition, regeneration of the biointerface was possible by low pH aqueous wash. Protein A from Staphylococcus aureus was also utilized to successfully increase the sensitivity for human IgG recognition (1.28 ± 0.11 mg/m(2)). Overall, the developed system based on TOCNF modified with multifunctional polymers can be easily deployed as bioactive material with minimum fouling and excellent selectivity.

Cellulose nanofibrils (CNF) were incorporated in water-in-oil (W/O) microemulsions and emulsions, as well as water-in-oil-in-water (W/O/W) multiple emulsions using soybean oil. The addition of CNF to the aqueous phase expanded the composition range to obtain W/O/W emulsions. CNF also increased the viscosity of the continuous phase and reduced the drop size both of which increased the stability and effective viscosity of the emulsions. The effects of oil type and polarity on the properties of the W/O/W emulsions were tested with limonene and octane, which compared to soybean oil produced a smaller emulsion drop size, and thus a higher emulsion viscosity. Overall, CNF are a feasible alternative to conventional polysaccharides as stability enhancers for normal and multiple emulsions that exhibit strong shear thinning behavior., (Copyright © 2014 Elsevier Inc. All rights reserved.)

One of the major, but often overlooked, challenges toward high end applications of nanocelluloses is to maintain their high mechanical properties under hydrated or even fully wet conditions. As such, permanent covalent cross-linking or surface hydrophobization are viable approaches, however, the former may hamper processability and the latter may have adverse effect on interfibrillar bonding and resulting material strength. Here we show a concept based on physical cross-linking of cellulose nanofibers (CNF, also denoted as microfibrillated cellulose, MFC, and, nanofibrillated cellulose, NFC) with chitosan for the aqueous preparation of films showing high mechanical strength in the wet state. Also, transparency (∼70-90% in the range 400-800 nm) is achieved by suppressing aggregation and carefully controlling the mixing conditions: Chitosan dissolves in aqueous medium at low pH and under these conditions the CNF/chitosan mixtures form easily processable hydrogels. A simple change in the environmental conditions (i.e., an increase of pH) reduces hydration of chitosan promoting multivalent physical interactions between CNF and chitosan over those with water, resulting effectively in cross-linking. Wet water-soaked films of CNF/chitosan 80/20 w/w show excellent mechanical properties, with an ultimate wet strength of 100 MPa (with corresponding maximum strain of 28%) and a tensile modulus of 4 and 14 GPa at low (0.5%) and large (16%) strains, respectively. More dry films of similar composition display strength of 200 MPa with maximum strain of 8% at 50% air relative humidity. We expect that the proposed, simple concept opens new pathways toward CNF-based material utilization in wet or humid conditions, which has still remained a challenge.

A new method to produce cellulose nanofibrils (CNF) is proposed to reduce the energy demand during deconstruction of precursor fibers suspended in aqueous media. Microemulsions were formulated with aqueous solutions of urea or ethylenediamine and applied to disrupt interfibril hydrogen bonding. Compared to typical fibrillation of lignin-containing and lignin-free fibers, pretreatment with microemulsion systems allowed energy savings during microfluidization of 55 and 32%, respectively. Moreover, microemulsion processing facilitated smaller-scale CNF structures (higher degrees of deconstruction), with higher water retention value (WRV) and surface area. Urea-containing microemulsions were found to be most effective in reducing energy consumption and in weakening the cellulosic matrix. Films prepared from CNF processed after pretreatment with urea-containing microemulsions presented a more uniform fiber network and produced films with smoother surfaces compared to those based on ethylenediamine. The lignin-containing CNF (LCNF) produced denser films than those obtained from lignin-free CNF. The mechanical properties of films obtained after application of microemulsion pretreatment were compared, and the benefits of the proposed approach were further confirmed. Overall, fiber deconstruction after microemulsion treatment is a step toward energy-efficient production of nanocellulose.

Hydrophobic particles based on dodecyl 3,4,5-trihydroxybenzoate (LG) were coupled onto the surface of cellulose nanofibrils (CNFs) and silica by treatment with a multicomponent colloidal system (MCS) derived from the laccase-mediated reaction of LG in the presence of a sulfonated lignin (SL). Surface modification upon treatment with MCS was monitored in situ and in real time by quartz crystal microgravimetry. The colloidal stability of MCS and its components in water was followed by measuring space- and time-resolved light transmission and back scattering. The sulfonated lignin increased dispersion stability and reduced the characteristic MCS particle size [from ≈4 to ≈80 nm, according to AFM and dynamic light scattering (DLS)]. It also facilitated the surface enzymatic reaction that led to adsorption and coupling of MCS onto CNFs and silica surfaces. The combined effect of reduced surface energy and surface roughness by MCS treatment produced an increase in water contact angle on CNFs and silica of about 90 and 80°, respectively. Surface pretreatment with chitosan further increased the extent of MCS adsorption on the surfaces. This method represents a sustainable alternative to traditional approaches for cellulose hydrophobization and a step forward in implementing green routes for surface modification., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The amount of residual lignin and hemicelluloses in softwood fibers was systematically varied by SO2-ethanol-water fractionation for integrated biorefinery with nanomaterial and biofuel production. On the basis of their low energy demand in mechanical processing, the fibers were deconstructed to lignocellulose nanofibrils (LCNF) and used as substrate for bioconversion. The effect of LCNF composition on saccharification via multicomponent enzymes was investigated at different loadings. LCNF digestibility was compared with the enzyme activity measured with a quartz crystal microbalance. LCNF hydrolysis rate gradually decreased with lignin and hemicellulose concentration, both of which limited enzyme accessibility. Enzyme inhibition resulted from non-productive binding of proteins onto lignin. Near complete LCNF hydrolysis was achieved, even at high lignin and hemicellulose content. Sugar yields for LCNF were higher than those for precursor SEW fibers, highlighting the benefits of high surface area in LCNF., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Films and hydrogels consisting of cellulose nanofibrils (CNF) were modified by covalent EDC/NHS coupling of luminescent, water-dispersible carbon dots (CDs). Quartz crystal microgravimetry with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) were used to investigate the attachment of CDs on carboxymethylated CNF (CM-CNF). As the first reported use of CD in nanocellulose products, we provide proof-of-concept for the synthesis of transparent and fluorescent nanopaper and for its tunable luminescence as confirmed by confocal microscopy imaging.

Cellulosic substrates were modified by using sequential adsorption of functionalized carboxymethyl cellulose (CMC) and "click" chemistry in aqueous media. First, the effect of degree of substitution (DS), and level of functionalization as well as ionic strength of the medium were systematically investigated in situ by using quartz crystal microbalance with dissipation (QCM-D) in terms of the extent of adsorption of propargyl and azido functionalized CMC. It was found that the functionalization of CMC did not prevent its adsorption on cellulose. However, it was only effective in the presence of electrolytes. Moreover, the adsorption was found to be more efficient for the functionalized CMCs with low initial DS. Next, "click" chemistry, copper (I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC), was carried out for covalent attachment of different molecules on the pre-functionalized ultrathin cellulose films. The modified cellulosic surfaces were further characterized using AFM imaging and XPS. Finally, the method was successfully used in modification of nanofibrillar cellulose (NFC) in aqueous media., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Novel hybrid nanomaterials have been developed for antimicrobial applications. Here we introduce a green route to produce antibacterial nanofiber mats loaded with silver nanoparticles (Ag-NPs, 25 nm diameter) enveloped in chitosan after reduction with glucose. The nanofiber mats were obtained from colloidal dispersions of chitosan-based Ag-NPs blended with polyvinyl alcohol. Nanofibers (150 nm average diameter and narrow size distribution) were obtained by electrospinning and cross-linked with glutaraldhyde. The effect of crosslinking on the release of silver was studied by atomic absorption spectroscopy. Antimicrobial activity was studied by the viable cell-counting; mats loaded with silver and control samples (chitosan/PVA) with different degrees of cross-linking were compared for their effectiveness in reducing or halting the growth of aerobic bacteria. The results showed superior properties and synergistic antibacterial effects by combining chitosan with Ag-NPs., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Bioactive films were produced by conjugation of a short peptide onto modified cellulose nanofibrils (CNF). Specifically, a hydrophilic copolymer, poly(2-aminoethyl methacrylate hydrochloride-co-2-hydroxyethylmethacrylate) (poly(AMA-co-HEMA)), was grafted via surface initiated polymerization from an initiator coupled to CNF. The poly(AMA-co-HEMA) was used as a spacer and support layer for immobilization of the peptide, acetylated-HWRGWVA, which has specific affinity with human immunoglobulin G (hIgG). Two methods for peptide grafting were compared: modification of CNF in aqueous suspension followed by assembly into a bioactive film and peptide grafting on a preformed CNF film. The CNF-based networks were examined on solid supports via atomic force microscopy (AFM) and extreme resolution imaging with ultralow electron landing energies (scanning low energy electron microscopy). The specific binding capability of hIgG and nonspecific protein resistance of the resultant peptide-modified CNF were evaluated by using quartz crystal microgravimetry (QCM). The effects of initiator concentration and thickness of poly(AMA-co-HEMA) layer on hIgG adsorption were investigated in the developed systems, which exhibited high signal-to-noise response.

We produced defect-free electrospun fibers from aqueous dispersions of lignin, poly(vinyl alcohol) (PVA), and cellulose nanocrystals (CNCs), which were used as reinforcing nanoparticles. The thermomechanical performance of the lignin-based electrospun fibers and the spin-coated thin films was improved when they were embedded with CNCs. Isochronal dynamic mechanical analysis (DMA) was used to assess the viscoelastic properties of the lignin:PVA electrospun fiber mats loaded with CNCs. DMA revealed that α relaxation processes became less prominent with an increased lignin content, an effect that correlated with the loss tangent (tan δ = E″/E') and α peak (Tg) that shifted to higher temperatures. This can be ascribed to the restraint of the segmental motion of PVA in the amorphous regions caused by strong intermolecular interactions. The reinforcing effect and high humidity stability attained by addition of CNCs (5, 10, or 15 wt %) in the multicomponent fiber mats were revealed. Nanoindentation was performed to assess the elastic modulus and hardness of as-prepared and cross-section surfaces of spin-coated lignin:PVA (75:25) films loaded with CNC. The properties of the two surfaces differed, and only the trend in cross-section elastic modulus correlated with DMA results. After addition of 5 wt % CNCs, both the DMA and nanoindentation elastic modulus remained constant, while after addition of 15 wt % CNCs, both increased substantially. An indentation size effect was observed in the nanoindentation hardness, and the results provided insight into the effect of addition of CNCs on the microphysical processes controlling the yield behavior in the composites.

We introduce a new method to modify films of nanofibrillated cellulose (NFC) to produce non-porous, water-resistant substrates for diagnostics. First, water resistant NFC films were prepared from mechanically disintegrated NFC hydrogel, and then their surfaces were carboxylated via TEMPO-mediated oxidation. Next, the topologically functionalized film was activated via EDS/NHS chemistry, and its reactivity verified with bovine serum albumin and antihuman IgG. The surface carboxylation, EDC/NHS activation and the protein attachment were confirmed using quartz crystal microbalance with dissipation, contact angle measurements, conductometric titrations, X-ray photoelectron spectroscopy and fluorescence microscopy. The surface morphology of the prepared films was investigated using confocal laser scanning microscopy and atomic force microscopy. Finally, we demonstrate that antihuman IgG can be immobilized on the activated NFC surface using commercial piezoelectric inkjet printing.

Lignin-based fibers were produced by electrospinning aqueous dispersions of lignin, poly(vinyl alcohol) (PVA), and cellulose nanocrystals (CNCs). Defect-free nanofibers with up to 90 wt % lignin and 15% CNCs were achieved. The properties of the aqueous dispersions, including viscosity, electrical conductivity, and surface tension, were examined and correlated to the electrospinnability and resulting morphology of the composite fibers. A ternary lignin-PVA-water phase diagram was constructed as a tool to rationalize the effect of mixing ratios on the dispersion electrospinability and morphology of the resulting fibers. The influence of reinforcing CNCs on the thermal properties of the multicomponent fibers was investigated by using thermal gravimetric analysis and differential scanning calorimetry. The thermal stability of the system was observed to increase owing to a strong interaction of the lignin-PVA matrix with the dispersed CNCs, mainly via hydrogen bonding, as observed in Fourier transform infrared spectroscopy experiments.

The effect of humidity on the morphological and thermomechanical properties of electrospun poly(vinyl alcohol) (PVA) fiber mats reinforced with cellulose nanocrystals (CNs) was investigated. Scanning electron microscopy (SEM) images revealed that the incorporation of CNs improved the morphological stability of the composite fibers even in high humidity environments. Thermal and mechanical properties of the electrospun fiber mats were studied by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and large deformation tensile tests under controlled humidity and temperatures. The balance between the moisture-induced plasticization and the reinforcing effect of rigid CN particles was critical in determining the thermomechanical behaviors of the electrospun fiber mats. Results indicated that the stabilizing effect of the CNs in the PVA matrix might be compromised by water absorption, disrupting the hydrogen bonding within the structure. The amount of this disruption depended on the surrounding humidity and the CN loading. The reduction in tensile strength of neat PVA fiber mats as they were conditioned from low relative humidity (10% RH) to high relative humidity (70% RH) was found to be about 80%, from 1.5 to 0.4 MPa. When the structure was reinforced with CNs, the reduction in strength was limited to 40%, from 2 to 0.8 MPa over the same range in relative humidity. More importantly, the CN-loaded PVA fiber mats showed a reversible recovery in mechanical strength after cycling the relative humidity. Finally, humidity treatments of the composite PVA fiber mats induced significant enhancement of their strength as a result of the adhesion between the continuous matrix and the CNs.

Cellulose nanocrystals (CN) were used to reinforce nanofibers in composite mats produced via electrospinning of poly(vinyl alcohol) (PVA) with two different concentrations of acetyl groups. Ultrathin cross-sections of the obtained nanocomposites consisted of fibers with maximum diameters of about 290 nm for all the CN loads investigated (from 0 to 15% CN loading). The electrospinning process did not affect the structure of the PVA polymer matrix, but its degree of crystallinity increased significantly together with a slight increase in the corresponding melting temperature. These effects were explained as being the result of alignment and enhanced crystallization of PVA chains within the individual nanofibers that were subjected to high shear stresses during electrospinning. The strong interaction of the PVA matrix with the dispersed CN phase, mainly via hydrogen bonding or bond network, was reduced with the presence of acetyl groups in PVA. Most importantly, the elastic modulus of the nanocomposite mats increased significantly as a consequence of the reinforcing effect of CNs via the percolation network held by hydrogen bonds. However, this organization-driven crystallization was limited as observed by the reduction in the degree of crystallinity of the CN-loaded composite fibers. Finally, efficient stress transfer and strong interactions were demonstrated to occur between the reinforcing CN and the fully hydrolyzed PVA electrospun fibers.

We studied the use of cellulose nanocrystals (CNXs) obtained after acid hydrolysis of ramie cellulose fibers to reinforce poly(epsilon-caprolactone) (PCL) nanofibers. Chemical grafting with low-molecular-weight PCL diol onto the CNXs was carried out in an attempt to improve the interfacial adhesion with the fiber matrix. Grafting was confirmed via infrared spectroscopy and thermogravimetric analyses. The polymer matrix consisted of electrospun nanofibers that were collected as nonwoven webs. The morphology as well as thermal and mechanical properties of filled and unfilled nanofibers were elucidated by scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis, respectively. The addition of CNXs into PCL produced minimal changes in the thermal behavior of the electrospun fibers. However, a significant improvement in the mechanical properties of the nanofibers after reinforcement with unmodified CNXs was confirmed. Fiber webs from PCL reinforced with 2.5% unmodified CNXs showed ca. 1.5-fold increase in Young's modulus and the ultimate strength compared to PCL webs. Compared to the case of grafted nanocrystals, the unmodified ones imparted better morphological homogeneity to the nanofibrillar structure. The grafted nanocrystals had a negative effect on the morphology of nonwoven webs in which individual nanofibers became annealed during the electrospinning process and, therefore, could not be compared to neat PCL nonwoven webs. A rationalization for the different effects of grafted and unmodified CNXs in reinforcing PCL nanofibers is provided.