Covalent Lysozyme Immobilization on Enzymatic Cellulose Nanocrystals.

Nanostructured materials represent promising substrates for biocatalysts immobilization and activation. Cellulose nanocrystals (CNCs), accessible from waste and/or renewable sources, are sustainable and biodegradable, show high specific surface area for anchoring a high number of enzymatic units, and high thermal and mechanical stability. In this work, we present a holistic enzyme-based approach to functional antibacterial materials by bioconjugation between the lysozyme from chicken egg white and enzymatic cellulose nanocrystals. The neutral CNCs were prepared by endoglucanase hydrolysis from Avicel. We explore the covalent immobilization of lysozyme on the enzymatic CNCs and on their TEMPO oxidized derivatives (TO-CNCs), comparing immobilization yields, materials properties, and enzymatic activities. The materials were characterized by X-ray diffractometry (XRD), attenuated total reflectance Fourier Transform infrared spectroscopy (ATR-FTIR), bicinchoninic acid (BCA) assay, field-emission scanning electron microscopy (FE-SEM) and dynamic light scattering (DLS). We demonstrate the higher overall efficiency of the immobilization process carried out on TO-CNCs, based on the success of covalent bonding and on the stability of the isolated biocojugates.

Production and Mechanical Characterisation of TEMPO-Oxidised Cellulose Nanofibrils/ß-Cyclodextrin Films and Cryogels.

Wood-based TEMPO-oxidised cellulose nanofibrils (toCNF) are promising materials for biomedical applications. Cyclodextrins have ability to form inclusion complexes with hydrophobic molecules and are considered as a method to bring new functionalities to these materials. Water sorption and mechanical properties are also key properties for biomedical applications such as drug delivery and tissue engineering. In this work, we report the modification with ß-cyclodextrin (ßCD) of toCNF samples with different carboxyl contents viz. 756 ± 4 µmol/g and 1048 ± 32 µmol/g. The modification was carried out at neutral and acidic pH (2.5) to study the effect of dissociation of the carboxylic acid group. Films processed by casting/evaporation at 40 °C and cryogels processed by freeze-drying were prepared from ßCD modified toCNF suspensions and compared with reference samples of unmodified toCNF. The impact of modification on water sorption and mechanical properties was assessed. It was shown that the water sorption behaviour for films is driven by adsorption, with a clear impact of the chemical makeup of the fibres (charge content, pH, and adsorption of cyclodextrin). Modified toCNF cryogels (acidic pH and addition of cyclodextrins) displayed lower mechanical properties linked to the modification of the cell wall porosity structure. Esterification between ßCD and toCNF under acidic conditions was performed by freeze-drying, and such cryogels exhibited a lower decrease in mechanical properties in the swollen state. These results are promising for the development of scaffold and films with controlled mechanical properties and added value due to the ability of cyclodextrin to form an inclusion complex with active principle ingredient (API) or growth factor (GF) for biomedical applications.

Current State and New Trends in the Use of Cellulose Nanomaterials for Wastewater Treatment.

Nanotechnology has been identified as having great potential for improving the efficiency of water prevention and purification while reducing costs. In this field, two applications of nanocellulose have generated attention and have proven to be a sound strategy as an adsorbent and as a membrane for the removal of contaminants. This potential is attributed to its high aspect ratio, high specific surface area, high capacity retention, and environmental inertness. In addition to the aforementioned advantages, the presence of active sites allows the incorporation of chemical moieties that may enhance the binding efficiency of pollutants to the surface. This review paper intends to understand how nanocellulose affects the adsorption behavior of water pollutants, e.g., heavy metal ions, microbes, dyes, and organic molecules, and is divided in two parts. First, a general overview of the different strategies for the preparation of nanocellulose is described, and its specific properties are reported. The second section reports some of its application as adsorbent nanomaterial or separation membrane. It appears that the use of nanocellulose for these applications is very promising for wastewater treatment industries.

Biomimetic Mineralization of Three-Dimensional Printed Alginate/TEMPO-Oxidized Cellulose Nanofibril Scaffolds for Bone Tissue Engineering.

The three-dimensional (3D) printed scaffolds were prepared by partial cross-linking of TEMPO-oxidized cellulose nanofibril/alginate hydrogel using calcium ions for printing the hydrogel while maintaining its shape, fidelity, and preventing the collapse of the filaments. The prepared scaffolds were fully cross-linked using calcium ions immediately after printing to provide the rigidity of the hydrogel and give it long-term stability. The composition of the prepared pastes was adjusted in view of the description of the hydrogel and 3D printing parameters. The rheological properties in terms of thixotropic behavior and viscosity recovery of hydrogels were investigated by performing steady shear rate experiments. The results show that the viscosity recovery for pure alginate hydrogel was only about 16% of the initial value, whereas it was 66% when adding cellulose nanofibrils to alginate. Consequently, the shape of the pure alginate scaffold was soft and easy to collapse contrarily to the composite scaffold. The biomimetic mineralization process of printed scaffolds using simulated body fluid, mimicking the inorganic composition of human blood plasma, was performed and the hydroxyapatite nucleation on the hydrogel was confirmed. The strength properties of the fabricated scaffolds in terms of compressive strength analysis were also investigated and discussed. The results show that the alginate/TEMPO-oxidized cellulose nanofibril system may be a promising 3D printing scaffold for bone tissue engineering.

Impregnation of paper with cellulose nanocrystal reinforced polyvinyl alcohol: synergistic effect of infrared drying and CNC content on crystallinity.

Paper was impregnated with neat polyvinyl alcohol (PVOH) or cellulose nanocrystal (CNC) reinforced PVOH, and dried by infrared radiation. Complex phenomena involved during paper impregnation and drying have been rarely investigated in the scientific literature, although these steps are crucial for the properties of the ensuing paper. The drying kinetics was studied and it showed that CNC tends to reduce the skin effect classically observed during fast PVOH drying. Furthermore, the nanoparticles induced faster water removal at the end of the drying step, which can be explained by an increase of the absorbed heat flux density. In addition, PVOH crystallization mechanisms have been studied through classical equations (Avrami, and Arrhenius) and a model (the Hoffman-Weeks method) and it was proved that both the drying conditions and the presence of CNC act on the crystallization of the polymer.

Cellulose nanomaterials as green nanoreinforcements for polymer nanocomposites.

Unexpected and attractive properties can be observed when decreasing the size of a material down to the nanoscale. Cellulose is no exception to the rule. In addition, the highly reactive surface of cellulose resulting from the high density of hydroxyl groups is exacerbated at this scale. Different forms of cellulose nanomaterials, resulting from a top-down deconstruction strategy (cellulose nanocrystals, cellulose nanofibrils) or bottom-up strategy (bacterial cellulose), are potentially useful for a large number of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, the basis for low-density foams, additives in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic and medical products. This paper focuses on the use of cellulose nanomaterials as a filler for the preparation of polymer nanocomposites. Impressive mechanical properties can be obtained for these materials. They obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. The emphasis is on the melt processing of such nanocomposite materials, which has not yet been properly resolved and remains a challenge.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Structural Reorganization of CNC in Injection-Molded CNC/PBAT Materials under Thermal Annealing.

Composite materials were prepared by extrusion and injection molding from polybutyrate adipate terephthalate (PBAT) and high aspect ratio cellulose nanocrystals (CNCs) extracted from capim dourado fibers. Three CNC contents were used, corresponding to 0.5, 1, and 2 times the theoretical percolation threshold. Small-amplitude oscillary shear (SAOS) experiments show that as the CNC content increases, a more elastic behavior is observed but no percolating network can form within the polymeric matrix as a result of the high shear rates involved during the injection-molding process. Annealing of the samples at 170 °C was performed, and the possible reorganization of the nanofiller was investigated. This reorganization was further elucidated using 2D-SAOS and creep experiments.

Chitosan-based aerogels: A new paradigm of advanced green materials for remediation of contaminated water.

Chitosan (CS) aerogels are highly porous (∼99 %), exhibit ultralow density, and are excellent sorbents for removing ionic pollutants and oils/organic solvents from water. Their abundant hydroxyl and amino groups facilitate the adsorption of ionic pollutants through electrostatic interaction, complexation and chelation mechanisms. Selection of suitable surface wettability is the way to separate oils/organic solvents from water. This review summarizes the most recent developments in improving the adsorption performance, mechanical strength and regeneration of CS aerogels. The structure of the paper follows the extraction of chitosan, preparation and sorption characteristics of CS aerogels for heavy metal ions, organic dyes, and oils/organic solvents, sequentially. A detailed analysis of the parameters that influence the adsorption/absorption performance of CS aerogels is carried out and their effective control for improving the performance is suggested. The analysis of research outcomes of the recently published data came up with some interesting facts that the unidirectional pore structure and characteristics of the functional group of the aerogel and pH of the adsorbate have led to the enhanced adsorption performance of the CS aerogel. Finally, the excerpts of the literature survey highlighting the difficulties and potential of CS aerogels for water remediation are proposed.

Supramolecular hydrogels from in situ host-guest inclusion between chemically modified cellulose nanocrystals and cyclodextrin.

When grafted ß-cyclodextrin is used as targeting sites, Pluronic polymers have been introduced on the surface of cellulose nanocrystals by means of inclusion interaction between ß-cyclodextrin and hydrophobic segment of the polymer. Because of the steric stabilization effect, surface poly(ethylene glycol) chains facilitate the dispersion and compatibility of nanocrystals, which also enhance the loading levels of nanocrystals in the hydrogel system. Meanwhile, uncovered poly(ethylene glycol) segments render the participating inclusion of α-cyclodextrin for the architecture of in situ hydrogels. Surface grafting and inclusion reactions were proved by solid (13)C NMR and FTIR. Grafting efficiency of ß-cyclodextrin and inclusion efficiency of Pluronic on the surface of nanocrystals were confirmed by UV spectroscopy and elemental analysis. A significant enhancement of the structural and thermal stability of in situ hydrogels with high loading levels of modified nanocrystals (>5.77 wt %) was observed by rheological analysis. Further study reveals the performance and behavior of hydrogels under a different pH environment. Finally, in situ hydrogels were used as drug carrier for in vitro release of doxorubicin and exhibit the behavior of prolonged drug release with special release kinetics.

Risedronate-loaded aerogel scaffolds for bone regeneration.

Sugarcane bagasse-derived nanofibrillated cellulose (NFC), a type of cellulose with a fibrous structure, is potentially used in the pharmaceutical field. Regeneration of this cellulose using a green process offers a more accessible and less ordered cellulose II structure (amorphous cellulose; AmC). Furthermore, the preparation of cross-linked cellulose (NFC/AmC) provides a dual advantage by building a structural block that could exhibit distinct mechanical properties. 3D aerogel scaffolds loaded with risedronate were prepared in our study using NFC or cross-linked cellulose (NFC/AmC), then combined with different concentrations of chitosan. Results proved that the aerogel scaffolds composed of NFC and chitosan had significantly improved the mechanical properties and retarded drug release compared to all other fabricated aerogel scaffolds. The aerogel scaffolds containing the highest concentration of chitosan (SC-T3) attained the highest compressive strength and mean release time values (415 ± 41.80 kPa and 2.61 ± 0.23 h, respectively). Scanning electron microscope images proved the uniform highly porous microstructure of SC-T3 with interconnectedness. All the tested medicated as well as unmedicated aerogel scaffolds had the ability to regenerate bone as assessed using the MG-63 cell line, with the former attaining a higher effect than the latter. However, SC-T3 aerogel scaffolds possessed a lower regenerative effect than those composed of NFC only. This study highlights the promising approach of the use of biopolymers derived from agro-wastes for tissue engineering.

Cellulose nanocrystals from agricultural residues (Eichhornia crassipes): Extraction and characterization.

Extraction of cellulose nanocrystals (CNCs) from agro-residues has received much attention, not only for their unique properties supporting a wide range of potential applications, but also their limited risk to global climate change. This research was conducted to assess Nile roses (Eichhornia crassipes) fibers as a natural biomass to extract CNCs through an acid hydrolysis approach. Nile roses fibers (NRFs) were initially subjected to alkaline (pulping) and bleaching pretreatments. Microcrystalline cellulose (MCC) was used as control in comparison to Nile rose based samples. All samples underwent acid hydrolysis process at a mild temperature (45 °C). The impact of extraction durations ranging from 5 to 30 min on the morphology structure and crystallinity index of the prepared CNCs was investigated. The prepared CNCs were subjected to various characterization techniques, namely: X-ray diffraction (XRD), FT-IR analysis, Transmission electron microscopy (TEM), and X-ray Photoelectron spectroscopy (XPS). The outcomes obtained by XRD showed that the crystallinity index increased as the duration of acid hydrolysis was prolonged up to 10 min, and then decreased, indicating optimal conditions for the dissolution of amorphous zones of cellulose before eroding the crystallized domains. These data were confirmed by FT-IR spectroscopy. However, a minor effect of hydrolysis duration on the degree of crystallinity was noticed for MCC based samples. TEM images illustrated that a spherical morphology of CNCs was formed as a result of 30 min acid hydrolysis, highlighting the optimal 20 min acid hydrolysis to obtain a fibrillar structure. The XPS study demonstrated that the main constituents of extracted CNCs were carbon and oxygen.

Use of lignin-based crude carbon dots as effective antioxidant for natural rubber.

Rubber is widely recognized as an important material, whose irreplaceable applications range from damping materials to tires. Generally, rubber is vulnerable to oxidative degradation, leading to a deterioration in the material's performance. Therefore, antioxidants are often added to extend the service life of rubber. In this study, crude lignin-based carbon dots (CLCDs) were prepared by a simple hydrothermal treatment of lignin with H2O2 and triethylenetetramine. The thus prepared CLCDs exhibit excellent radical scavenging capability, and were incorporated into natural rubber with vinyl pyridine-styrene-butadiene terpolymer (VPR) as coupling agent. The results revealed that CLCDs could endow NR with excellent antioxidative performance. Interestingly, CLCDs even show superior antioxidant effect towards rubber compared to purified lignin-based carbon dots (PLCDs). This work provides a unique source of inspiration for the preparation of low-cost, highly effective CLCDs from plant biomass waste, most of lignin being used to produce steam and energy, with excellent antioxidant capability for rubber, which is beneficial for a green and sustainable world.

Enzymatic pretreatment for preparing starch nanocrystals.

Starch nanocrystals (SNCs) are crystalline platelets resulting from the acid hydrolysis of starch. A limiting factor for their more widespread use is their preparation duration. Therefore, this study investigates the possibility of developing an enzymatic pretreatment of starch to reduce the acid hydrolysis duration. A screening of three types of enzymes, namely, α-amylase, ß-amylase, and glucoamylase, is proposed, and the latter was selected for a pretreatment. Compared with the regular kinetics of hydrolysis for preparing SNC, that of pretreated starch was much faster. The extent of hydrolysis normally reached in 24 h was obtained after only 6 h, and the regular final yield (15% after 5 days) was reached in 45 h. AFM and X-ray diffraction measurements confirmed that the obtained nanoparticles were indeed SNC.

Synergistic reinforcing and cross-linking effect of thiol-ene-modified cellulose nanofibrils on natural rubber.

To achieve synergistic reinforcing and cross-linking effect across interface between hydrophilic nanocellulose and hydrophobic rubber, active thiol groups were introduced at reducing end of CNF while retaining hydroxyl groups on the surface, thus forming a percolation network in nanocomposites. The nanocomposites were obtained by casting/evaporating a mixture of dispersed modified CNF and NR in latex form, in which covalent cross-links were formed between thiol groups and double bonds of NR via photochemically initiated thiol-ene reaction. Strong interfacial interaction between NR matrix and end-modified CNF was characterized by Fourier-transform infrared spectroscopy. The structural and mechanical properties of the nanocomposites were evaluated by scanning electron microscopy, dynamic mechanical analysis and tensile tests. Compared to neat NR, the nanocomposite reinforced with 10 wt% modified CNF showed significantly higher values of tensile strength (0.33 to 5.83 MPa), Young's modulus (0.48 to 45.25 MPa) and toughness (2.63 to 22.24 MJ m-3).

Oxidation treatments to convert paper-grade Eucalyptus kraft pulp into microfibrillated cellulose.

Microfibrillated cellulose (MFC) is an emerging cellulosic material that has shown enormous potential in various industrial sectors such as food packaging, cosmetics, pharmaceuticals, filler for cement and paper, and others. Yet, there is still the need to improve its processing in order to reach its full potential. Despite research efforts for the production of MFC, the production volumes remain low because the costs of these products are hardly competitive with synthetic polymers. The present study investigates the conversion of bleached Kraft pulp into MFC using three different oxidative treatments: (1) oxidation with sodium periodate followed by oxidation with hydrogen peroxide to enrich the pulp with carboxyl groups; (2) activation of hydrogen peroxide with copper to produce hydroxyl radicals; and (3) use of hydrogen peroxide alone in alkaline medium. Treatments (1) and (2) allowed producing interesting MFC with reduced energy consumption.

Recent advances in lignin-based carbon materials and their applications: A review.

As the most abundant natural aromatic polymer, tens of million of tons of lignin produced in paper-making or biorefinery industry are used as fuel annually, which is a low-value utilization. Moreover, burning lignin results in large amounts of carbon dioxide and pollutants in the air. The potential of lignin is far from being fully exploited and the search for high value-added application of lignin is highly pursued. Because of the high carbon content of lignin, converting lignin into advanced carbon-based structural or functional materials is regarded as one of the most promising solutions for both environmental protection and utilization of renewable resources. Significant progresses in lignin-based carbon materials (LCMs) including porous carbon, activated carbon, carbon fiber, carbon aerogel, nanostructured carbon, etc., for various valued applications have been witnessed in recent years. Here, this review summarized the recent advances in LCMs from the perspectives of preparation, structure, and applications. In particular, this review attempts to figure out the intrinsic relationship between the structure and functionalities of LCMs from their recent applications. Hopefully, some thoughts and discussions on the structure-property relationship of LCMs can inspire researchers to stride over the present barriers in the preparation and applications of LCMs.

Nanocellulose-based aerogel electrodes for supercapacitors: A review.

Recently, in response to the challenges related to energy development and environmental issues, extensive efforts are being made towards the development of supercapacitors based on green and sustainable resources. Aerogel electrodes offer high energy/power autonomy, fast charge-discharge rates, and long charge/discharge cycles over composite film electrodes due to their unique structure, ultra-lightness, high porosity, and large specific surface area. Nanocellulose (NC), a sustainable nanomaterial, has gained popularity as a supercapacitor electrode material owing to its remarkable properties such as biodegradability, tunable surface chemistry, ability to develop 3D aerogel structures, etc. This comprehensive review summarizes the research progress on developing NC-based aerogels for supercapacitor applications. First, the fundamentals of NC extraction from cellulose sources and aerogel processing routes are discussed. An attempt is made to correlate the electrochemical performance of NC-based electrodes with their aerogel structures. Finally, challenges and future prospects for the advancement of NC-based aerogels are addressed.

Alternative modification by grafting in bamboo cellulose nanofibrils: A potential option to improve compatibility and tunable surface energy in bionanocomposites.

Chemical modification in surface of cellulose nanofibrils CNFs (20 nm) from an endemic and non-significant value-added, Argentine bamboo, was developed. The modification in the CNFs was carried out with three simple routes using a low molecular weight polylactic acid synthesized in our laboratory (PLA1). The first step comprises of protection of the hydroxyl groups of PLA1 through a benzoylation (PLA1Bz). The next step consisted of the activation of carboxyl groups using thionyl chloride and the last reaction was the grafting of the modified PLA onto the CNFs (PLA1Bz-g-CNF). The covalently functionalization is confirmed by spectroscopically techniques as well as PLA1Bz-g-CNFs were characterized by thermal analyses. The PLA1Bz-g-CNFs were taken up such as nanocharges to improve properties of compatibilization and changing surface properties in films based on PLA. The comparison between the films with PLA1Bz-g-CNFs with respect to the physic mixture of the components (PLA1Bz/CNF), shows an improvement in the thermal, mechanical, and surface properties of the material, particularly when 5% of PLA1Bz-g-CNFs was added. The dispersive (γS D) component of film is increased in 36.1 mN/m respect to 29.3 mN/m from the films obtained with the physic mixture nanofibrils without modification and a plasticizing effect was noticed in the final material.

Cellulose nanocrystals-reinforced core-shell hydrogels for sustained release of fertilizer and water retention.

Core-shell (CS) hydrogels show great potential for the controlled release of fertilizers. In this work, we prepared an alginate-coated gelatin-cellulose nanocrystals (CNCs) hydrogel by a simple layer-by-layer process. CNCs were prepared from cotton linter fibers by the sulfuric acid process. They were incorporated into the gelatin hydrogel, and an external alginate membrane was applied to the inner membrane. Compared to neat gelatin hydrogel, the compressive modulus of the nanocomposite with 5.0 wt% CNCs was enhanced by 288 %. In addition, the CS hydrogel showed a slow-release property and better water retention capacity than neat gelatin hydrogel. The main results of this work are listed below: compression test revealed that the addition of the CNC increases the mechanical properties of the hydrogel, and ii) the addition of a second layer of alginate to CNC-reinforced gelatin hydrogel increase the water retention and improve the sustained release of fertilizer. Our study provides easy and green routes to produce CS hydrogels for potential agricultural applications.

Evidence of micro- and nanoscaled particles during starch nanocrystals preparation and their isolation.

Great work has been done to reduce the batch production time of starch nanocrystals (SNCs) and improve their compatibilization with different matrices. However, only one study was reported on SNC production kinetics and none on size distributions and isolation techniques. This study was designed to assess if nonsolubilized particles in the hydrolyzed starch suspension reflect the actual amount of SNC. It was observed that SNCs are produced from a very early stage. It suggests, for the first time, that (i) nanocrystals are mixed together with other microparticles and (ii) some nanocrystals might turn to sugar by the end of the batch production process explaining the low yields. An isolation process has been proposed, but limits of differential centrifugations as washing step and isolation technique were also evidenced. This study clearly shows the need for a continuous production and extraction process of SNC.