Self-organized films from cellulose I Nanofibrils using the layer-by-layer technique

Structure-properties relationships of defined CNF single-networks crosslinked by telechelic PEGs

The high structural anisotropy and colloidal stability of cellulose nanofibrils' enable the creation of self-standing fibrillar hydrogel networks at very low solid contents. Adding methacrylate moieties on the surface of TEMPO oxidized CNFs allows the formation of more robust covalently crosslinked networks by free radical polymerization of acrylic monomers, exploiting the mechanical properties of these networks more efficiently. This technique yields strong and elastic networks but with an undefined network structure. In this work, we use acrylate-capped telechelic polymers derived from the step-growth polymerization of PEG diacrylate and dithiothreitol to crosslink methacrylated TEMPO-oxidized cellulose nanofibrils (MATO CNF). This combination resulted in flexible and strong hydrogels, as observed through rheological studies, compression and tensile loading. The structure and mechanical properties of these hydrogel networks were found to depend on the dimensions of the CNFs and polymer crosslinkers. The structure of the networks and the role of individual components were evaluated with SAXS (Small-Angle X-ray Scattering) and photo-rheology. A thorough understanding of hybrid CNF/polymer networks and how to best exploit the capacity of these networks enable further advancement of cellulose-based materials for applications in packaging, soft robotics, and biomedical engineering.

Process design for acidic and alcohol based deep eutectic solvent pretreatment and high pressure homogenization of palm bunches for nanocellulose production

This research aimed to study on nanocellulose production from palm bunch using process design and cost analysis. Choline chloride based deep eutectic solvent pretreatment was selected for high-purity cellulose separation at mild condition, followed by nano-fibrillation using mechanical treatment. Three types of choline chloride-based deep eutectic solvents employing different hydrogen-bond donors (HBDs) namely lactic acid, 1,3-butanediol and oxalic acid were studied. The optimal cellulose extraction condition was choline chloride/lactic acid (ChLa80C) pretreatment of palm empty bunch at 80 °C followed by bleaching yielding 94.96%w/w cellulose content in product. Size reduction using ultrasonication and high-pressure homogenization produced nanocellulose at 67.12%w/w based on cellulose in raw material. Different morphologies of nanocellulose were tunable in the forms of nanocrystals, nano-rods and nanofibers by using dissimilar deep eutectic solvents. This work offered a sustainable and environmentally friendly process as well as provided analysis of DES pretreatment and overview operating cost for nanocellulose production. Application of nanocellulose for the fabrication of highly functional and biodegradable material for nanomedicine, electronic, optical, and micromechanical devices is achievable in the near future.

Advanced Functionalized Materials Based on Layer-by-Layer Assembled Natural Cellulose Nanofiber for Electrodes: A Review

The depletion of fossil fuel resources and its impact on the environment provide a compelling motivation for the development of sustainable energy sources to meet the increasing demand for energy. Accordingly, research and development of energy storage devices have emerged as a critical area of focus. The electrode materials are critical in the electrochemical performance of energy storage devices, such as energy storage capacity and cycle life. Cellulose nanofiber (CNF) represents an important substrate with potentials in the applications of green electrode materials due to their environmental sustainability and excellent compatibility. By utilizing the layer-by layer (LbL) process, well-defined nanoscale multilayer structure is prepared on a variety of substrates. In recent years, increasing attention has focused on electrode materials produced from LbL process on CNFs to yield electrodes with exceptional properties, such as high specific surface area, outstanding electrical conductivity, superior electrochemical activity, and exceptional mechanical stability. This review provides a comprehensive overview on the development of functional CNF via the LbL approach as electrode materials.

Recycling of TEMPO-mediated oxidation medium and its effect on nanocellulose properties

The potential of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy)-mediated oxidation (TMO) to produce cellulose nanofibrils (CNFs) is hindered using costly and environmentally harmful catalysts, limiting its large-scale implementation. To promote sustainability, the TMO medium should be reused but there is a lack of knowledge on this process. The novelty of this research is the identification of the key parameters that affect the recirculation of the TMO medium, and their impact on the quality of the oxidized pulps and CNF products. Contrary to previous hypothesis, results show that the accumulation of salts is not a key parameter; instead, the pulp consistency during oxidation plays a vital role since concentrations higher than 10 g/L led to better CNF quality. Thus, reusing 75 % of the reaction medium, when high pulp consistency is used, does not alter the CNF properties. By reusing the reaction medium up to six times, the catalyst dose is dramatically reduced by >90 % for TEMPO and 80 % for NaBr, compared to the conventional process (0.1 mmol of TEMPO/g and 1 mmol of NaBr/g without medium reuse). Additionally, the high consistency oxidation enables a reduction of >80 % in the reaction time and effluent, and thus a threefold increase in CNF production.

Shape-recovering nanocellulose networks: Preparation, characterization and modeling

Development of strong cellulose nanofibril (CNF) networks for advanced applications, such as in the biomedical field, is of high importance owing to the biocompatible nature and plant-based origin of cellulose nanofibrils. Nevertheless, lack of mechanical strength and complex synthesis methods hinder the application of these materials in areas where both toughness and manufacturing simplicity are required. In this work, we introduce a facile method for the synthesis of a low solid content (< 2 wt%), covalently crosslinked CNF hydrogel where Poly (N-isopropylacrylamide) (NIPAM) chains are utilized as crosslinks between the nanofibrils. The resulting networks have the capability to fully recover the shape in which they were formed after various drying and rewetting cycles. Characterization of the hydrogel and its constitutive components was performed using X-ray scattering, rheological investigations and uniaxial testing in compression. Influence of covalent crosslinks was compared with networks crosslinked by the addition of CaCl₂. Among other things the results show that the mechanical properties of the hydrogels can be tuned by controlling the ionic strength of the surrounding medium. Finally, a mathematical model was developed based on the experimental results, which describes and predicts to a decent degree the large-deformation, elastoplastic behavior, and fracture of these networks.

Tunable poly(lauryl methacrylate) surface grafting via SI-ATRP on a one-pot synthesized cellulose nanofibril macroinitiator core as a shear-thinning rheology modifier and drag reducer

The optimally one-pot synthesized 2-bromoproponyl esterified cellulose nanofibril (Br-CNF) has been validated as a robust macroinitiator for self-surface-initiated atom transfer radical polymerization (SI-ATRP) of lauryl methacrylate (LMA) in tunable graft lengths and high conversions of up to 92.7%. SI-ATRP of LMA surface brushes on Br-CNF followed first order kinetics in lengths at up to 46 degree of polymerization (DP) based on mass balance or 31 DP by solution-state 1H NMR in DMSO-d6. With increasing PLMA graft lengths, Br-CNF-g-PLMA cast films exhibited increasing hydrophobicity with water contact angles from 80.9° to 110.6°. The novel Br-CNF-g-PLMA exhibited dual shear thinning behavior of the Br-CNF core as evident by n < 1 flow behavior index and drag reducing properties of PLMA grafts with increased viscosity at up to 21 071×. Br-CNF-g-PLMA with 46 DP could be fully dispersed in silicon pump oil to function as a drag reducer to enhance viscosity up to 5× at 25, 40, and 55 °C. The novel macroinitiator capability of Br-CNF in SI-ATRP of vinyl monomers and the bottlebrush-like LMA surface grafted Br-CNF as highly effective viscosity modifier and drag reducer further demonstrate the versatile functionality of Br-CNF beyond hydrophobic coatings and reactive polyols previously reported.

Unraveling the control of reversibility for actuators based on cellulose nanofibers

In this work, we have prepared cellulose-based actuators taking advantage of the pH-sensitive solubility of chitosan (CH) and the mechanical strength of CNFs. Bilayer films were prepared by vacuum filtration inspired by plant structures that exhibit reversible deformation under pH changes. The presence of CH in one of the layers led to asymmetric swelling at low pH, thanks to the electrostatic repulsion between charged amino groups of CH, and the subsequent twisting with the CH layer on the outside. Reversibility was achieved by substituting pristine CNFs with carboxymethylated CNFs (CMCNFs), that are charged at high pH and thus competed with the effects of amino groups. Swelling and mechanical properties of layers under pH changes were studied by gravimetry and dynamic mechanical analysis (DMA) to quantify the contribution of chitosan and the modified CNFs on the reversibility control. This work evidenced the key role of surface charge and layer stiffness to achieve reversibility. Bending was triggered by the different water uptake of each layer, and shape recovery was achieved when the shrunk layer shower higher rigidity than the swollen layer.

Production of nanocellulose using acidic deep eutectic solvents based on choline chloride and carboxylic acids: A review

Nowadays, nanocellulose production processes with numerous merits of green, eco-friendly, and cost-effective are in urgent need. Acidic deep eutectic solvent (ADES), as an emerging green solvent, has been widely applied in the preparation of nanocellulose over the past few years, owing to its unique advantages, including non-toxicity, low cost, easy synthesis, recyclability, and biodegradability. At present, several studies have explored the effectiveness of ADESs in nanocellulose production, particularly those based on choline chloride (ChCl) and carboxylic acids. Various acidic deep eutectic solvents have been employed, with representative ones such as ChCl-oxalic/lactic/formic/acetic/citric/maleic/levulinic/tartaric acid. Herein, we comprehensively reviewed the latest progress of these ADESs, focusing on the treatment procedures and key superiorities. In addition, the challenges and outlooks of ChCl/carboxylic acids-based DESs implementation in the fabrication of nanocellulose were discussed. Finally, some suggestions were proposed to advance the industrialization of nanocellulose, which would help for the roadmap of sustainable and large-scale production of nanocellulose.

The Colloidal Properties of Nanocellulose

Nanocelluloses are anisotropic nanoparticles of semicrystalline assemblies of glucan polymers. They have great potential as renewable building blocks in the materials platform of a more sustainable society. As a result, the research on nanocellulose has grown exponentially over the last decades. To fully utilize the properties of nanocelluloses, a fundamental understanding of their colloidal behavior is necessary. As elongated particles with dimensions in a critical nanosize range, their colloidal properties are complex, with several behaviors not covered by classical theories. In this comprehensive Review, we describe the most prominent colloidal behaviors of nanocellulose by combining experimental data and theoretical descriptions. We discuss the preparation and characterization of nanocellulose dispersions, how they form networks at low concentrations, how classical theories cannot describe their behavior, and how they interact with other colloids. We then show examples of how scientists can use this fundamental knowledge to control the assembly of nanocellulose into new materials with exceptional properties. We hope aspiring and established researchers will use this Review as a guide.

Biobased Nanomaterials─The Role of Interfacial Interactions for Advanced Materials

This review presents recent advances regarding biomass-based nanomaterials, focusing on their surface interactions. Plant biomass-based nanoparticles, like nanocellulose and lignin from industry side streams, hold great potential for the development of lightweight, functional, biodegradable, or recyclable material solutions for a sustainable circular bioeconomy. However, to obtain optimal properties of the nanoparticles and materials made thereof, it is crucial to control the interactions both during particle production and in applications. Herein we focus on the current understanding of these interactions. Solvent interactions during particle formation and production, as well as interactions with water, polymers, cells and other components in applications, are addressed. We concentrate on cellulose and lignin nanomaterials and their combination. We demonstrate how the surface chemistry of the nanomaterials affects these interactions and how excellent performance is only achieved when the interactions are controlled. We furthermore introduce suitable methods for probing interactions with nanomaterials, describe their advantages and challenges, and introduce some less commonly used methods and discuss their possible applications to gain a deeper understanding of the interfacial chemistry of biobased nanomaterials. Finally, some gaps in current understanding and interesting emerging research lines are identified.

2-Bromopropionyl Esterified Cellulose Nanofibrils as Chain Extenders or Polyols in Stoichiometrically Optimized Syntheses of High-Strength Polyurethanes

2-Bromopropionyl bromide esterified cellulose nanofibrils (Br-CNFs) facilely synthesized from one-pot esterification of cellulose and in situ ultrasonication exhibited excellent N,N-dimethylformamide (DMF) dispersibility and reactivity to partially replace either chain extender or soft segment diol in the stoichiometrically optimized syntheses of polyurethanes (PUs). PUs polymerized with Br-CNF to replace either 11 mol% 1,4-butadiol chain extender OHs or 1.8 mol% polytetramethylene ether glycol OHs, i.e., 1.5 or 0.3 wt% Br-CNF in PUs, exhibited an over 3 times increased modulus, nearly 4 times higher strength, and a 50% increase in strain. In either role, the experimental modulus exceeding those predicted by the Halpin-Tsai model gave evidence of the stoichiometrically optimized covalent bonding with Br-CNF, while the improved strain was attributed to increased hydrogen-bonding interactions between Br-CNF and the soft segment. These new Br-CNFs not only offer novel synthetic strategies to incorporate nanocelluloses in polyurethanes but also maximize their reinforcing effects via their versatile polyol reactant and cross-linking roles, demonstrating promising applications in the synthesis of other polymers.

Cellulose nanofibers/polyvinyl alcohol blends as an efficient coating to improve the hydrophobic and oleophobic properties of paper

The effect of cellulose nanofibers (CNFs)/polyvinyl alcohol (PVA) coating on the hydrophobic, oleophobic, and strength properties of paper were investigated. The results showed that the size of bamboo fibers (BFs) decreased significantly and the crystallinity increased significantly after biological enzyme treatment. The average length of CNFs obtained by high pressure homogenization was 2.4 µm, the diameter was 28.7 nm, and the crystallinity was 63.63%. When the coating weight of PVA/CNF was 2.0 g/m² and the CNF dosage was increased from 0.0% to 3.0%, the paper grease resistance grade was increased from 7 to 9, the Cobb value was decreased from 22.68 ± 0.29 g/m² to 18.37 ± 0.63 g/m², the contact angle was increased from 67.82° to 93.56°, and the longitudinal and transverse tensile index were increased from 67.72 ± 0.21 N m/g and 37.63 ± 0.25 N m/g to 68.61 ± 0.55 N m/g and 40.71 ± 0.78 N m/g, respectively. When the CNF dosage was 3.0% and the coating weight of PVA/CNF was 4.0 g/m², the grease resistance grade of the paper was 12, the Cobb value was 21.80 ± 0.39 g/m², and the longitudinal and transverse tensile indices were 72.11 ± 0.43 N m/g and 42.58 ± 0.48 N m/g, respectively. In summary, the increase of CNFs can effectively improve the lipophobicity, hydrophobicity and tensile strength of the PVA coated paper.

Effect of cationization pretreatment on the properties of cationic Eucalyptus micro/nanofibrillated cellulose

Micro/nanofibrillated celluloses (M/NFCs) have attracted considerable research interest over the past few decades, with various pretreatments being used to reduce energy consumption and/or increase fibrillation. To date, few studies have considered cationization as a pretreatment for their preparation. In this work, quaternary ammonium groups were attached to cellulose fibers by a direct reaction with 2,3-epoxypropyltrimethylammonium chloride or by a two-step method (periodate oxidation + Girard's reagent T). The cationic fibers with degrees of substitution (DS) between 0.02 and 0.36, were subjected to homogenization treatment. The morphological properties, chemical composition, and rheological behavior were evaluated to assess the effect of DS and the effect of the cationization method (for samples with similar DS). The two-step cationization resulted in significant degradation of the cellulose structure, leading to the formation of short fibrils and solubilization of the material, ranging from 6% to almost complete solubilization at a DS of 0.36. Direct cationization resulted in longer fibrils with an average diameter of 1 μm, and no significant cellulose degradation was observed, leading to a more cohesive gel-like material (at 1 wt%). These observations clearly show the strong influence of the cationization method on the final properties of the cationic cellulosic materials.

One-pot synthesis of 2-bromopropionyl esterified cellulose nanofibrils as hydrophobic coating and film

Bromo-esterified cellulose nanofibrils have been one-pot synthesized by direct heterogeneous 2-bromopropionyl esterification and in situ ultra-sonication to serve as versatile hydrophobic nm thick coating or 100 μm thick film.

TOCNC-g-PEI nanoparticle encapsulated oregano essential oil for enhancing the antimicrobial activity of cellulose nanofibril packaging films

A nanocellulose-based film with excellent antimicrobial and antioxidant activity was developed by adding Pickering emulsion which was stabilized by functionalized particles. First, TOCNC-g-PEI nanoparticles were prepared by grafting polyethyleneimine (PEI) onto TEMPO-oxidized cellulose nanocrystals (TOCNCs) and used to stabilize oregano essential oil (OEO) Pickering emulsions. The contact angle of TOCNC-g-PEI nanoparticles was 79.7°, and the minimum inhibitory concentration against L.monocytogenes and E.coli was 0.50 mg/mL. Second, the emulsion droplets were stably dispersed in cellulose nanofibril (CNF) suspensions owing to the depletion stability of CNFs. Finally, the films were dried and emulsion droplets formed oil core/CNF shell microcapsules in active CNF films and completely encapsulated OEO in active CNF films. The inhibition rates of the film against L.monocytogenes and E.coli were 97.28% and 97.23%, respectively. The influence of Pickering emulsion on the active CNF films was discussed. The developed active CNF films have promising application in food preservation and active packaging.

Recent Developments in Cellulose Nanomaterial Composites

Cellulose nanomaterials (CNMs) are a class of materials that have recently garnered attention in fields as varied as structural materials, biomaterials, rheology modifiers, construction, paper enhancement, and others. As the principal structural reinforcement of biomass giving wood its mechanical properties, CNM is strong and stiff, but also nontoxic, biodegradable, and sustainable with a very large (Gton yr^-1 ) source. Unfortunately, due to the relatively young nature of the field and inherent incompatibility of CNM with most man-made materials in use today, research has tended to be more basic-science oriented rather than commercially applicable, so there are few CNM-enabled products on the market today. Herein, efforts are presented for preparing and forming cellulose nanomaterial nanocomposites. The focus is on recent efforts attempting to mitigate common impediments to practical commercialization but is also placed in context with traditional efforts. The work is presented in terms of the progress made, and still to be made, on solving the most pressing challenges-getting properties that are competitive with currently used materials, removing organic solvent, solving the inherent incompatibility between CNM and polymers of interest, and incorporation into commonly used industrial processing techniques.

The Use of Layer-by-Layer Self-Assembly and Nanocellulose to Prepare Advanced Functional Materials

The current knowledge about the formation of layer-by-layer (LbL) self-assemblies using combinations of nanocelluloses (NCs) and polyelectrolytes is reviewed. Herein, the fundamentals behind the LbL formation, with a major focus on NCs, are considered. Following this, a special description of the limiting factors for the formation of LbLs of only NCs, both anionic and cationic, and the combination of NCs and polyelectrolytes/nanoparticles is provided. The ability of the NCs and polyelectrolytes to form dense films with excellent mechanical properties and with tailored optical properties is then reviewed. How low-density, wet stable networks of cellulose nanofibrils can be used as substrates for the preparation of antibacterial, electrically interactive, and fire-retardant materials by forming well-defined LbLs inside these networks is then considered. A short outlook of the possible uses of LbLs containing NCs is given to conclude.

Sustainable isolation of nanocellulose from cellulose and lignocellulosic feedstocks: Recent progress and perspectives

As a type of sustainable nanomaterials, nanocellulose has drawn increasing attention over the last two decades due to its great potential in diverse value-added applications such as electronics, sensors, energy storage, packaging, pharmaceuticals, biomedicine, and functional food. Sourcing nanocellulose from lignocellulose is commonly accomplished via the use of mineral acids, oxidizers, enzymes, and/or intensive mechanical energy. Yet, the economic and environmental concerns associated with these conventional isolation techniques pose major obstacles for commercialization. Considerable progress has been achieved in the last few years in developing sustainable nanocellulose isolation technologies involving organic acid/anhydride, Lewis acid, solid acid, ionic liquid, and deep eutectic solvent. This paper provides a comprehensive review of these alternatives with regard to general procedures and key advantages. Important knowledge gaps, including total biomass utilization, complete life cycle analysis, and health/safety, require urgently bridging in order to develop economically competitive and operationally feasible nanocellulose isolation technology for commercialization.

Ultrathin Films of Cellulose: A Materials Perspective

A literature review on ultrathin films of cellulose is presented. The review focuses on different deposition methods of the films-all the way from simple monocomponent films to more elaborate multicomponent structures-and the use of the film structures in the vast realm of materials science. The common approach of utilizing cellulose thin films as experimental models is therefore omitted. The reader will find that modern usage of cellulose thin films constitutes an exciting emerging area within materials science and it goes far beyond the traditional usage of the films as model systems.

Tuning the Nanoscale Properties of Phosphorylated Cellulose Nanofibril-Based Thin Films To Achieve Highly Fire-Protecting Coatings for Flammable Solid Materials

Ultrathin nanocomposite films were prepared by combining cellulose nanofibrils (CNFs) prepared from phosphorylated pulp fibers (P-CNF) with montmorillonite (MMT), sepiolite (Sep) clay, or sodium hexametaphosphate (SHMP). The flame-retardant and heat-protective capability of the prepared films as casings for a polyethylene (PE) film was investigated. Heating the coated PE in air revealed that the polymer film was thoroughly preserved up to at least 300 °C. The P-CNF/MMT coatings were also able to completely prevent the ignition of the PE film during cone calorimetry, but neither the P-CNF/Sep nor the P-CNF/SHMP coating could entirely prevent PE ignition. This was explained by the results from combined thermogravimetry Fourier transform infrared spectroscopy, which showed that the P-CNF/MMT film was able to delay the release of PE decomposition volatiles and shift its thermal degradation to a higher temperature. The superior flame-retardant performance of the P-CNF/MMT films is mainly attributed to the unique compositional and structural features of the film, where P-CNF is responsible for increasing the char formation, whereas the MMT platelets create excellent barrier and thermal shielding properties by forming inorganic lamellae within the P-CNF matrix. These films showed a tensile strength of 304 MPa and a Young's modulus of 15 GPa with 10 wt % clay so that this composite film was mechanically stronger than the previously prepared CNF/clay nanopapers containing the same amount of clay.

Recent Strategies in Preparation of Cellulose Nanocrystals and Cellulose Nanofibrils Derived from Raw Cellulose Materials

The recent strategies in preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were described. CNCs and CNFs are two types of nanocelluloses (NCs), and they possess various superior properties, such as large specific surface area, high tensile strength and stiffness, low density, and low thermal expansion coefficient. Due to various applications in biomedical engineering, food, sensor, packaging, and so on, there are many studies conducted on CNCs and CNFs. In this review, various methods of preparation of CNCs and CNFs are summarized, including mechanical, chemical, and biological methods. The methods of pretreatment of cellulose are described in view of the benefits to fibrillation.

Development of high throughput, high precision synthesis platforms and characterization methodologies for toxicological studies of nanocellulose

Cellulose is one of the most abundant natural polymers, is readily available, biodegradable, and inexpensive. Recently, interest is growing around nanoscale cellulose due to the sustainability of these materials, the novel properties, and the overall low environmental impact. The rapid expansion of nanocellulose uses in various applications makes the study of the toxicological properties of these materials of great importance to public health regulators. However, most of the current toxicological studies are highly conflicting, inconclusive, and contradictory. The major reasons for these discrepancies are the lack of standardized methods to produce industry-relevant reference nanocellulose and relevant characterization that will expand beyond the traditional cellulose characterization for applications. In order to address these issues, industry-relevant synthesis platforms were developed to produce nanocellulose of controlled properties that can be used as reference materials in toxicological studies. Herein, two types of nanocellulose were synthesized, cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) using the friction grinding platform and an acid hydrolysis approach respectively. The nanocellulose structures were characterized extensively regarding their physicochemical properties, including testing for endotoxins and bacteria contamination.

All-natural and highly flame-resistant freeze-cast foams based on phosphorylated cellulose nanofibrils

Pure cellulosic foams suffer from low thermal stability and high flammability, limiting their fields of application. Here, light-weight and flame-resistant nanostructured foams are produced by combining cellulose nanofibrils prepared from phosphorylated pulp fibers (P-CNF) with microfibrous sepiolite clay using the freeze-casting technique. The resultant nanocomposite foams show excellent flame-retardant properties such as self-extinguishing behavior and extremely low heat release rates in addition to high flame penetration resistance attributed mainly to the intrinsic charring ability of the phosphorylated fibrils and the capability of sepiolite to form heat-protective intumescent-like barrier on the surface of the material. Investigation of the chemical structure of the charred residue by FTIR and solid state NMR spectroscopy reveals the extensive graphitization of the carbohydrate as a result of dephosphorylation of the modified cellulose and further dehydration due to acidic catalytic effects. Originating from the nanoscale dimensions of sepiolite particles, their high specific surface area and stiffness as well as its close interaction with the phosphorylated fibrils, the incorporation of clay nanorods also significantly improves the mechanical strength and stiffness of the nanocomposite foams. The novel foams prepared in this study are expected to have great potential for application in sustainable building construction.

Robust Guar Gum/Cellulose Nanofibrils Multilayer Films with Good Barrier Properties

The pursuit of sustainable functional materials requires development of materials based on renewable resources and efficient fabrication methods. Hereby, we fabricated all-polysaccharides multilayer films using cationic guar gum (CGG) and anionic cellulose nanofibrils (i.e., TEMPO-oxidized cellulose nanofibrils, TOCNs) through a layer-by-layer casting method. This technique is based on alternate depositions of oppositely charged water-based CGG and TOCNs onto laminated films. The resultant polyelectrolyte multilayer films were transparent, ductile, and strong. More importantly, the self-standing films exhibited excellent gas (water vapor and oxygen) and oil barrier performances. Another outstanding feature of these resultant films was their resistance to various organic solvents including methanol, acetone, N,N-dimethylacetamide (DMAc) and tetrahydrofuran (THF). The proposed film fabrication process is environmentally benign, cost-effective, and easy to scale-up. The developed CGG/TOCNs multilayer films can be used as a renewable material for industrial applications such as packaging.

Use of CdS quantum dot-functionalized cellulose nanocrystal films for anti-counterfeiting applications

Structural colors and photoluminescence have been widely used for anti-counterfeiting and security applications. We report for the first time the use of CdS quantum dot (QD)-functionalized cellulose nanocrystals (CNCs) as building blocks to fabricate nanothin films via layer-by-layer (LBL) self-assembly for anti-counterfeiting applications. Both negatively- and positively-charged CNC/QD nanohybrids with a high colloidal stability and a narrow particle size distribution were prepared. The controllable LBL coating process was characterized by scanning electron microscopy and ellipsometry. The rigid structure of CNCs leads to nanoporous structured films on poly(ethylene terephthalate) (PET) substrates with high transmittance (above 70%) over the entire range of visible light and also resulted in increased hydrophilicity (contact angles of ∼40 degrees). Nanothin films on PET substrates showed good flexibility and enhanced stability in both water and ethanol. The modified PET films with structural colors from thin-film interference and photoluminescence from QDs can be used in anti-counterfeiting applications.

Nisin anchored cellulose nanofibers for long term antimicrobial active food packaging

Increasing consumer demand for high performance bio-based materials in order to develop microbiologically safer foods has forced the food industry to revise their packaging strategies.

Reversible modification of structure and properties of cellulose nanofibril-based multilayered thin films induced by postassembly acid treatment

A postassembly acid-treatment consisting of an immersion in 5 mM HCl solution was applied to carboxylated cellulose nanofibrils (CNF)-poly(allylamine) hydrochloride (PAH) multilayered thin films. Our results show that the treatment did not affect the overall thickness of the films without any loss of the components. However, a modification of the surface morphology was observed, as well as the swelling behavior. The process was perfectly reversible since the original structure was recovered when the thin films were rinsed by ultrapure water. Moreover, a more pronounced antireflective character was detected for the treated films. The origin of these reversible modifications was discussed. Notably, the scattering length density (SLD) profiles of the films before and after treatment support the idea of a structural reorganization of the components within the film driven by the change of their charge densities induced by the acid treatment.

Fast and reversible direct CO2 capture from air onto all-polymer nanofibrillated cellulose-polyethylenimine foams

Fully polymeric and biobased CO2 sorbents composed of oxidized nanofibrillated cellulose (NFC) and a high molar mass polyethylenimine (PEI) have been prepared via a freeze-drying process. This resulted in NFC/PEI foams displaying a sheet structure with porosity above 97% and specific surface area in the range 2.7-8.3 m(2)·g(-1). Systematic studies on the impact of both PEI content and relative humidity on the CO2 capture capacity of the amine functionalized sorbents have been conducted under atmospheric conditions (moist air with ∼400 ppm of CO2). At 80% RH and an optimum PEI content of 44 wt %, a CO2 capacity of 2.22 mmol·g(-1), a stability over five cycles, and an exceptionally low adsorption half time of 10.6 min were achieved. In the 20-80% RH range studied, the increase in relative humidity increased CO2 capacity of NFC/PEI foams at the expense of a high H2O uptake in the range 3.8-28 mmol·g(-1).

Cellulose nanofibril-based multilayered thin films: effect of ionic strength on porosity, swelling, and optical properties

TEMPO-oxidized cellulose nanofibrils (CNF) and synthetic poly(allylamine) hydrochloride (PAH) were used to build multilayered thin films via the dipping-assisted layer-by-layer technique. We used the ionic strength, in both CNF suspension and PAH solution, as a key parameter to control the structure of the films. Three systems with different ionic strength parameters were investigated. We studied the growth of the films and their surface morphology by ellipsometry and AFM and investigated their porosity and swelling behavior using neutron reflectivity. Our results showed that the PAH conformation is a determining factor not only for film growth but also for structural properties: with salt-free PAH solution where chains have extended conformation, the resulting films have lower porosity and higher swelling ratios, compared to the ones made using high ionic strength (1 M) PAH solution, where chains have a coiled conformation. The slight aggregation of CNF, induced by adding a small amount of salt (12 mM), has less influence on film growth and porosity, whereas it has a greater impact on swelling. The origin of these differences is discussed. The structure of the films obtained was linked to their optical properties and, in particular, to their antireflective character.

Towards biomimicking wood: fabricated free-standing films of Nanocellulose, Lignin, and a synthetic polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

Transparent nanocellulosic multilayer thin films on polylactic acid with tunable gas barrier properties

The layer-by-layer (LbL) deposition method was used for the build-up of alternating layers of nanofibrillated cellulose (NFC) or carboxymethyl cellulose (CMC) with a branched, cationic polyelectrolyte, polyethyleneimine (PEI) on flexible poly (lactic acid) (PLA) substrates. With this procedure, optically transparent nanocellulosic films with tunable gas barrier properties were formed. 50 layer pairs of PEI/NFC and PEI/CMC deposited on PLA have oxygen permeabilities of 0.34 and 0.71 cm(3)·μm/m(2)·day·kPa at 23 °C and 50% relative humidity, respectively, which is in the same range as polyvinyl alcohol and ethylene vinyl alcohol. The oxygen permeability of these multilayer nanocomposites outperforms those of pure NFC films prepared by solvent-casting. The nanocellulosic LbL assemblies on PLA substrates was in detailed characterized using a quartz crystal microbalance with dissipation (QCM-D). Atomic force microscopy (AFM) reveals large structural differences between the PEI/NFC and the PEI/CMC assemblies, with the PEI/NFC assembly showing a highly entangled network of nanofibrils, whereas the PEI/CMC surfaces lacked structural features. Scanning electron microscopy images showed a nearly perfect uniformity of the nanocellulosic coatings on PLA, and light transmittance results revealed remarkable transparency of the LbL-coated PLA films. The present work demonstrates the first ever LbL films based on high aspect ratio, water-dispersible nanofibrillated cellulose, and water-soluble carboxymethyl cellulose polymers that can be used as multifunctional films and coatings with tailorable properties, such as gas barriers and transparency. Owing to its flexibility, transparency and high-performance gas barrier properties, these thin film assemblies are promising candidates for several large-scale applications, including flexible electronics and renewable packaging.

Nanofibrillated Cellulose Surface Modification: A Review

Interest in nanofibrillated cellulose (NFC) has increased notably over recent decades. This bio-based nanomaterial has been used essentially in bionanocomposites or in paper thanks to its high mechanical reinforcement ability or barrier property respectively. Its nano-scale dimensions and its capacity to form a strong entangled nanoporous network have encouraged the emergence of new high-value applications. It is worth noting that chemical surface modification of this material can be a key factor to achieve a better compatibility with matrices. In order to increase the compatibility in different matrices or to add new functions, surface chemical modification of NFC appears to be the prior choice to conserve its intrinsic nanofibre properties. In this review, the authors have proposed for the first time an overview of all chemical grafting strategies used to date on nanofibrillated cellulose with focus on surface modification such as physical adsorption, molecular grafting or polymer grafting.