TEMPO-oxidized Cellulose Nanocrystals Research Articles

Structural analyses of supernatant fractions in TEMPO-oxidized pulp/water reaction mixtures separated by centrifugation and dialysis

Side reactions occurring on cellulose during 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TMEPO)-catalyzed oxidation have not been considered to be significant. Then, TEMPO-oxidized hardwood and softwood bleached kraft pulps (HBKP and SBKP) were prepared with an excess NaOCl·5H2O. Supernatant fractions (SFs) were obtained in the aqueous reaction mixtures of TEMPO-oxidized pulps by centrifugation and dialysis. The SFs with carboxyl contents of 5.0 and 4.2 mmol/g were obtained in the yields of 19 % and 30 % from HBKP and SBKP, respectively. These carboxy contents are much higher than those (2.6–2.7 mmol/g) of the precipitate fractions in the TEMPO-oxidized pulps. Solid-state 13C NMR spectra and other analyses revealed that the water-soluble β-(1 → 4)-polyglucuronic acids were predominantly present in the SFs. In addition, water-insoluble TEMPO-oxidized cellulose nanocrystals were present in the SFs, but they constituted less than ~10 % of the SFs. The mass-average degrees of polymerization (DPw) of the SFs obtained from HBKP and SBKP were 166 and 155, respectively, whereas the original HBKP and SBKP had DPw values of 1990 and 2140, respectively. These substantial depolymerization and formation of the water-soluble β-(1 → 4)-polyglucuronic acids occur on cellulose and oxidized cellulose molecules as side reactions during TEMPO-catalyzed oxidation, which should be considered for structural analyses of TEMPO-oxidized products.

Effect of cellulose nanocrystals-loaded ginger essential oil emulsions on the physicochemical properties of mung bean starch composite film

The poor antibacterial and water resistance of starch film hinder its application in packaging and preservation field. In this study, the green composite films were prepared via incorporating ginger essential oil (GEO) Pickering emulsions stabilized by tempo-oxidized cellulose nanocrystals (TOCN) into a starch-based film-forming matrix. The results showed the TOCN-loaded GEO emulsion dispersed well in the mung bean starch film. The antibacterial activity and tensile strength (TS) of the composite films were improved with the insertion of TOCN-loaded GEO. When the amount of TOCN was 1.0 wt% and the GEO dosage was 22%, compared with the control film, the water vapor permeability of the composite films declined by 60.3%, and the TS improved by 25.0%, and the composite films also showed high antibacterial activity. Additionally, the study on storage ability showed that the new compound starch-based films had a better storage effect on tomatoes. The prepared composite films have considerable potential for packaging applications. • The GEO Pickering emulsions stabilized by TOCN was successfully prepared. • The prepared starch-based composited film had good strength, hydrophobic property and antibacterial property. • The starch-based composited film with TOCN/GEO had a better storage effect on tomatoes.

Efficient visual adsorption of Pb2+ by nanocellulose/sodium alginate microspheres with fluorescence sensitivity

In this study, carbon dots (CDs) were prepared by a one-pot hydrothermal method using tempo-oxidized cellulose nanocrystals (TOCNC) and polyethylenimine (PEI). The CDs were self-assembled with a microsphere adsorbent prepared using TOCNC and sodium alginate (SA). CDs-TOCNC/SA—an environmentally friendly, fluorescent-sensitive, and recyclable microsphere adsorbent—was obtained. FTIR analysis showed that PEI successfully modified the CDs. In addition, the fluorescence quenching of CDs was observed when the concentration of Pb2+ was 0.0001–100 mg/L, indicating that CDs can dynamically monitor Pb2+. CDs-TOCNC/SA can produce blue fluorescence under 365 nm UV light and selectively and efficiently adsorb Pb2+. When the concentration of Pb2+ was 0.0001–100 mg/L, fluorescence quenching of the adsorbent was observed, indicating that CDs-TOCNC/SA could visually adsorb Pb2+. The adsorption isotherm and kinetic parameters show that the adsorption process conforms to the Langmuir isotherm model at 298 K, and the maximum adsorption capacity of Pb2+ was 190.1 mg/g at pH = 5. Moreover, CDs-TOCNC/SA could still obtain 78.99 % Pb2+ after five sorption-desorption cycles. The adsorption mechanism may involve ion exchange, electrostatic attraction, intra-particle diffusion, and chemical complexation.

Nanoengineering the Redispersibility of Cellulose Nanocrystals.

Enhancing the redispersibility of dried colloidal particles to yield stable dispersions after rehydration is a persistent challenge in the sustainable processing of nanocelluloses due to hydrogen bonding-induced irreversible aggregation. Programming nanocelluloses, such as cellulose nanocrystals (CNC), with moieties that enable colloidal repulsion after rehydration may address this challenge and contribute to the United Nation (UN)'s sustainable development goals (SDGs) of urban development and sustainable living (SDGs 9 and 11) and cradle-to-cradle processing (SDG 12). We hypothesize that imparting electrosteric repulsion to CNC via polyanionic disordered cellulose chains (hairs) protruding from each end may render the dried nanocrystals highly redispersible in aqueous media. Anionic hairy CNC (AHCNC), that is, CNC decorated with dicarboxylated cellulose (DCC) chains, were synthesized by the preferential, successive periodate/chlorite oxidation of the disordered regions of cellulose fibrils, bearing >5 mmol of carboxylate groups per gram. The colloidal properties of AHCNC were compared with those of sulfate half-ester group-functionalized CNC and TEMPO-oxidized CNC (TOCNC) after redispersion in aqueous media, followed by comparing the redispersibility of AHCNC and CNC in aqueous solutions containing monovalent or divalent cations and at varying pH. The AHCNC had remarkable aqueous redispersibility even at high ionic strengths and extreme pH. The unique redispersibility mechanism of dried AHCNC relies on the synergistic steric and electrostatic repulsion forces, recuperated upon the rehydration of DCC. This work may open new opportunities for more sustainable and cost-effective handling and processing of nanocelluloses.

Preparation, properties, and mechanism of anionic and cationic cellulose nanocrystals/waterborne polyurethane composite films

Three kinds of cellulose nanocrystals (CNCs) were added into waterborne polyurethane (WPU) and nanocomposite films that were prepared by solution casting. The influence of different ionic function groups on microstructure and properties of composite films was investigated. Compared with sulfated CNCs (SCNCs) and TEMPO oxidized CNCs (TOCNCs), FE-SEM images showed that cationized CNCs (CaCNCs) had better dispersion in composite films. The thermal decomposition of these composite films was delayed by 15 °C compared with pure WPU film. The tensile strength and fracture work of CaCNC/WPU composite film increased by 11.9% and 8.4%, respectively. The light transmittance of CaCNC/WPU composite film was highest among the 3 composite films, but its oxygen permeability was the lowest. In sum, the composite film with CaCNCs had optimal strength, toughness, light transmittance, and oxygen barrier properties, which is consistent with good compatibility of the two components and densest structure observed in SEM. There may be an ionic attraction and hydrogen bonds of CaCNCs and WPU in the composite film. The composite films are expected to have applications in food packaging, furniture coatings, and biomedical fields.

Tailored synthesis of ultra-stable Au@Pd nanoflowers with enhanced catalytic properties using cellulose nanocrystals

A green strategy for the synthesis of bimetallic core-shell Au@Pd nanoflowers (NFs) employing banana pseudo-stem-derived TEMPO-oxidized cellulose nanocrystals (TCNC) as both capping and shape-directing agent via seed-mediated method is presented. Flower-like nanostructures of Au@Pd bound to TEMPO-oxidized cellulose nanocrystals (TCNC-Au@Pd) were decorated on amino-functionalized graphene (NH2-RGO) without losing their unique structure, allowing them to be deployed as an efficient, reusable and a green alternative heterogeneous catalyst. The decisive role of TCNC in the structural metamorphosis of nanoparticle morphology were inferred from the structural and morphology analyses. According to our study, the presence of –OH rich TCNC appears to play a pivotal role in the structured evolution of intricate nanostructure morphology. The feasibility of the bio-supported catalyst has been investigated in two concurrently prevalent model catalytic reactions, namely the oxygen reduction reaction (ORR) and the reduction of 4-nitrophenol, the best model reactions in fuel cell and industrial catalytic applications, respectively.

Design and fabrication of recyclable and reshape vitrified elastomer reinforced with renewable cellulose nanocrystal

Developing the recyclable elastomeric vitrimer with dynamic covalent bonds is a very promising strategy to alleviate the burden of traditional vulcanized rubber materials on the environment. In this work, we proposed to introduce epoxidized soybean oil (ESO) as a cross-linking agent into carboxyl nitrile butadiene rubber (XNBR)/TEMPO-oxidized cellulose nanocrystals (TO-CNC) composites, and successfully prepared ESO-cured XNBR/TO-CNC elastomeric vitrimer with dynamic β-hydroxyl ester bonds, which are formed between the epoxy group of ESO and the carboxyl group of XNBR or TO-CNC. The TEMPO oxidation of CNC is validated by a series of characterizations such as FTIR, conductometric titration, and element analysis. The formation of the β-hydroxyl esters is as well evidenced by the FTIR analysis and the curing curves. Interestingly, the TO-CNC exhibits good dispersion in the composite, and a remarkable mechanical reinforcement is observed for ESO-cured XNBR/TO-CNC elastomer, for instance, the tensile strength of the composite with 15 phr TO-CNC was 2.4 times greater than that of the unfilled sample. Moreover, this composite as well shows good reshaping capability and reprocessability. Generally, this work offers a novel approach to preparing green cross-linked elastomer/bio-based CNC composites that can potentially overcome the bottleneck of the non-recycling of traditional vulcanized rubber.

Supramolecular modulation of the mechanical properties of amino acid-functionalized cellulose nanocrystal films

Cellulose nanocrystal (CNC) is a promising building block for the bottom-up assembly of novel lightweight renewable materials. The ability to engineer the interfacial properties of CNC is of paramount importance to develop assembled materials for various applications; yet it remains a challenge to manipulate the supramolecular interactions within the cellulosic nanomaterials in a controlled manner. In this context, we demonstrate in this article how the assembly and mechanical properties of cellulose thin films can be controlled by manipulating the interfacial interactions of TEMPO-oxidized cellulose nanocrystals (TOCNCs) grafted with two different amino acids, arginine and tryptophan. The amino acid grafting onto the cellulose scaffold was confirmed in aqueous solutions by 1H NMR spectroscopy and in solid form by FTIR and XPS techniques. The surface functionalization of TOCNCs with simple cationic and aromatic groups provides a strategy for tuning the assembly of the nanostructures based on different supramolecular cross-linking interactions, including hydrogen bonds, π–π stacking, and cation–π interactions. In particular, we show that nanocellulose chains cross-linked by the non-covalent cation–π interactions lead to the formation of a laminated superstructure with high deformation and load standing capabilities. Our work provides a versatile strategy for tuning the surface properties of nanocellulose and represents an important step toward the development of sustainable materials with tailored mechanical properties, which will enable a wider application range of this building block all the way from tissue-engineering scaffolds to flexible devices.

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.

Cellulose nanocrystals directed in-situ assembly of Au@Ag nanostructures with multifunctional activities

Bio-template-directed synthesis of shell-engineered plasmonic nano-assemblies has attracted extensive research interest due to their profound opto-electronic properties. Herein, we report TEMPO-oxidized cellulose nanocrystals (TCNC) as a promising bio-template for the in-situ preparation and assembly of Aucore-Agshell nanoparticles (Au@Ag NPs) having excellent colloidal stability with tunable optical and catalytic properties. By modulating Ag shell thickness, TCNC promoted the assembly of Au@Ag nanostructures and resulted in abundant plasmonic hotspots. Thereby as-formed TCNC payloads could enhance its solid-state SERS activity in detecting malachite green and methylene blue concentration down to 10 fM and 100 fM, respectively. The finite element modelling (FEM) studies further supported the observed results, revealing the enhanced electric field concentrates at the junction of two adjacent TCNC-Au@Ag NPs as the origin of augmentation in the SERS signals. Further, TCNC-Au@Ag NPs assemblies showed superior catalytic activity towards 4-nitrophenol reduction with a rate constant of 32.33 × 10−3 s−1.

Theoretical Rationalization of Self-Assembly of Cellulose Nanocrystals: Effect of Surface Modifications and Counterions.

The hierarchical self-assembly of cellulose nanocrystals (CNCs) is an important phenomenon occurring naturally in plant cell walls. Utilization of this assembly for advanced applications requires a fundamental theoretical understanding of interactions between the CNCs, which is still incomplete. Hence, in this work, we used molecular dynamics simulations to study the effect of surface modification on the interactions between the CNCs and the resulting bundling process. We consider two types of common surface modifications of native CNCs, sulfated CNCs (SCNCs) and TEMPO-oxidized CNCs (TCNCs), in the presence of two types of counterions, Na+ and Ca2+, in solution. We used the umbrella sampling method to calculate the potential of the mean force (PMF), and we found that the strength of interaction between the modified CNCs decreases, compared with the native CNCs. The strength of interaction for TCNCs is almost similar to that for SCNCs at the same level of surface substitution, whereas the type of counterion has a strong effect on the PMF with a higher interaction energy between the CNCs in the presence of a divalent counterion as compared to a monovalent counterion. Finally, we studied the self-assembly of CNCs into a hexagonal bundle for the native CNCs and sulfated CNCs focusing on the twist of the bundle, bound water inside the bundle, inter-CNC gap, and interaction energy between the CNCs in the bundle, and the effect of the counterions on the morphology of the bundle. The equilibrium spacing of the CNCs within the bundle is found to be consistent with the results of PMF calculations for the minimum separation distance between the respective crystal surfaces.

Amidation of TEMPO-oxidized cellulose nanocrystals using aromatic aminated molecules

In this study, the grafting of 1-methyl-3-phenylpropylamine (1-M-3-PP) on cellulose nanocrystals (CNCs) via a two-step reaction route was investigated and compared with physico-chemical surface adsorption. The first step involved subjecting CNCs to a 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO)-mediated oxidation. The carboxylic groups present on recovered oxidized TEMPO-CNC were quantified by several characterization methods (conductometric titration, elemental analysis, and X-ray photoelectron spectroscopy), and a degree of oxidation close to 0.2 was found. The second step was an amidation reaction carried out in an aqueous medium under mild conditions and in the presence of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC)/N-hydroxysuccinimide (NHS) as catalyst. The recovered modified CNCs after amidation reaction with 1-M-3-PP (CNC-1-M-3-PP) were extensively washed and then characterized. The amount of grafted molecules was determined by several techniques like X-ray photoelectron spectroscopy (XPS), and the calculated degree of substitution was found to be close to 0.05 with respect to the bulk CNC. This low amount is sufficient to enhance the modified CNC dispersion and their colloidal stabilization in organic solvents, allowing the preparation of nanocomposites. Furthermore, such CNC-1-M-3-PP units with aromatic molecules attached to it can find applications in barrier materials in which the sorption of aromatic molecules can be very useful.

Heparin Mimic Material Derived from Cellulose Nanocrystals

This study analyzes and evaluates the use of cellulose nanocrystals (CNCs), stiff nanosized natural materials that have been modified to mimic heparin. These CNCs are simple polysaccharides with a similar backbone structure to heparin, which when modified reduces coagulation and potentially the long-term effects of solution-based anticoagulants. Thus, CNCs represent an ideal foundation for generating materials biocompatible with blood. In this study, we developed a biocompatible material that inhibits blood clotting through surface functionalization to mimic heparin. Surface chemistry of CNCs was modified from "plain" CNCs (70 mmol SO3-/kg) to 500 mmol COO-/kg (TEMPO-oxidized CNCs) and 330 mmol SO3-/kg CNCs (sulfonated CNCs). Platelet adherence and blood assays show that changes in functionalization reduce coagulation. By utilizing and modifying CNCs reactive functional groups, we create a material with unique and favorable mechanical properties while also reducing clotting.

Effect of cellulose nanocrystals on the performance of oil-immersed transformer insulating paper

The possibility of enhancing both mechanical and breakdown properties of oil-immersed transformer insulating paper were considered by introduction of cellulose nanocrystals (CNCs). Two kinds of CNCs were taken into account: the TEMPO-oxidized CNCs (T-CNC) and the sulfuric acid hydrolyzed CNCs (S-CNC). Insulating paper containing no CNCs was also prepared as a reference. Obtained samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The effects of different amounts of CNC on tensile strength, AC breakdown strength, oil absorption rate, and conductivity of insulating paper extract were studied. The CNC improved the mechanical and electrical performances of insulating paper, and the effect of T-CNC was a little better than that of S-CNC. When the T-CNC dosage was 0.9%, the tensile strength, AC breakdown strength in oil, and oil absorption rate of the insulating paper were 70.22 N • m/g, 59.8 kV/mm, and 53.1%, respectively, which was improved by 21.7%, 24.6%, and 39.4%, respectively, compared with the reference insulating paper. The beating degree of pulp also affected the mechanical and electrical properties of insulating paper containing CNC. Based on overall performance, it was concluded that CNCs are promising nano-additives for oil-immersed transformer insulating paper, especially for T-CNC.

Reduced graphene oxide and PEG-grafted TEMPO-oxidized cellulose nanocrystal reinforced poly-lactic acid nanocomposite film for biomedical application.

In this work, both cellulose nanocrystals (CNC) and reduced graphene oxide (rGO) were reinforced into poly-lactic acid (PLA) to enhance the stiffness, strength and thermal stability of the pure polymer i.e. PLA. To enhance the uniform dispersion of CNC (which is a major concern with PLA) and rGO in the hydrophobic polymer matrix, CNC's surface was first modified using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation method followed by surface grafting of TEMPO-oxidized CNC (TOCNC) performed with polyethylene glycol (PEG). The PEG-grafting on crystalline region of cellulose nanofibrils was achieved through ionic bonds by applying ion-exchange method (simple and easy method). The obtained PEG-grafted-TOCNC indicated uniform dispersion at the nanoelement level in non-polar (organic) compound i.e. chloroform. Further, the PEG-grafted-TOCNC/chloroform with different blend ratios, PLA/chloroform and rGO/chloroform solution were mixed together and solvent casted onto a petri-dish to obtain PLA/PEG-TOCNC/rGO nanocomposite film. The tensile strength and thermal stability were remarkably improved for the film containing highest wt% of modified CNC. In addition to this, the film showed reduced water vapor barrier properties and antioxidant activity which enables it to be used as a packaging films. Moreover, the film displayed negligible toxicity and cytocompatibility to fibroblast cells C3H10T1/2. These attractive properties of PLA/PEG-TOCNC/rGO nanocomposite film render the application of film as a scaffold in tissue engineering field and in packaging application.

Preparation of silver nanoparticles using different fractions of TEMPO-oxidized nanocellulose

The aim of this study was to examine efficacy of different fractions of TEMPO-oxidized cellulose nanocrystals (TOCNs) as a reducing and capping agent of silver nanoparticles (AgNPs). Silver nanoparticles were prepared by thermal treatment of AgNO3 in aqueous suspensions of TOCN fractions. Three different nanocomposite materials based on different fractions of TOCNs and reduced in situ by TOCN silver nanoparticles were obtained. It was demonstrated that three fractions of TOCNs, characterised by varying water-solubility, degree of oxidation and viscosity, bind silver nanoparticles differently. The capping of anionic TOCNs fractions on the surface of nanoparticles was confirmed by zeta potential measurements, and therefore good stability of AgTOCNs nanoparticles was shown. The size and dispersion of AgNPs seems to be affected mainly by the viscosity of a given TOCN fraction. Water-soluble TOCN fractions yielded spherical AgNPs, while water-insoluble fractions contributed to the formation of nanoparticles characterised by diverse morphologies. The application of TEMPO-oxidized cellulose fractions for greener synthesis of silver nanoparticles is discussed. A mechanism including a polylol process is proposed as a possible means of silver cation reduction. The morphology and structural features of the TOCN nanocellulose-silver nanoparticle composites were assessed with the use of spectroscopic and microscopic techniques.

Functionalized Cellulose Nanocrystal Nanocomposite Membranes with Controlled Interfacial Transport for Improved Reverse Osmosis Performance.

Thin-film nanocomposite membranes (TFNs) are a recent class of materials that use nanoparticles to provide improvements over traditional thin-film composite (TFC) reverse osmosis membranes by addressing various design challenges, e.g., low flux for brackish water sources, biofouling, etc. In this study, TFNs were produced using as-received cellulose nanocrystals (CNCs) and 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs) as nanoparticle additives. Cellulose nanocrystals are broadly interesting due to their high aspect ratios, low cost, sustainability, and potential for surface modification. Two methods of membrane fabrication were used in order to study the effects of nanoparticle dispersion on membrane flux and salt rejection: a vacuum filtration method and a monomer dispersion method. In both cases, various quantities of CNCs and TOCNs were incorporated into a polyamide TFC membrane via in-situ interfacial polymerization. The flux and rejection performance of the resulting membranes was evaluated, and the membranes were characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The vacuum filtration method resulted in inconsistent TFN formation with poor nanocrystal dispersion in the polymer. In contrast, the dispersion method resulted in more consistent TFN formation with improvements in both water flux and salt rejection observed. The best improvement was obtained via the monomer dispersion method at 0.5 wt% TOCN loading resulting in a 260% increase in water flux and an increase in salt rejection to 98.98 ± 0.41% compared to 97.53 ± 0.31% for the plain polyamide membrane. The increased flux is attributed to the formation of nanochannels at the interface between the high aspect ratio nanocrystals and the polyamide matrix. These nanochannels serve as rapid transport pathways through the membrane, and can be used to tune selectivity via control of particle/polymer interactions.

Three-Dimensional Stable Alginate-Nanocellulose Gels for Biomedical Applications: Towards Tunable Mechanical Properties and Cell Growing.

Hydrogels have been studied as promising materials in different biomedical applications such as cell culture in tissue engineering or in wound healing. In this work, we synthesized different nanocellulose-alginate hydrogels containing cellulose nanocrystals, TEMPO-oxidized cellulose nanocrystals (CNCTs), cellulose nanofibers or TEMPO-oxidized cellulose nanofibers (CNFTs). The hydrogels were freeze-dried and named as gels. The nanocelluloses and the gels were characterized by different techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA), while the biological features were characterized by cytotoxicity and cell growth assays. The addition of CNCTs or CNFTs in alginate gels contributed to the formation of porous structure (diameter of pores in the range between 40 and 150 μm). TEMPO-oxidized cellulose nanofibers have proven to play a crucial role in improving the dimensional stability of the samples when compared to the pure alginate gels, mainly after a thermal post-treatment of these gels containing 50 wt % of CNFT, which significantly increased the Ca2+ crosslinking density in the gel structure. The morphological characteristics, the mechanical properties, and the non-cytotoxic behavior of the CNFT-alginate gels improved bioadhesion, growth, and proliferation of the cells onto the gels. Thus, the alginate-nanocellulose gels might find applications in tissue engineering field, as for instance, in tissue repair or wound healing applications.

Acid-Free Preparation of Cellulose Nanocrystals by TEMPO Oxidation and Subsequent Cavitation.

Softwood bleached kraft pulp (SBKP) and microcrystalline cellulose (MCC) were oxidized using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated system. The TEMPO-oxidized SBKP prepared with 10 mmol/g NaClO (SBKP-10) had a higher mass recovery ratio and higher carboxylate content than the other prepared celluloses including the TEMPO-oxidized MCCs. The SBKP-10 was then exposed to cavitation-induced forces through sonication in water for 10-120 min to prepare aqueous dispersions of needle-like TEMPO-oxidized cellulose nanocrystals (TEMPO-CNCs) with homogeneous width of 3.5 to 3.6 nm and average lengths of ∼200 nm. The average chain lengths of the cellulose molecules that make up the TEMPO-CNCs were less than half the average lengths of the TEMPO-CNCs. Compared with conventional CNCs prepared by acid hydrolysis, the TEMPO-CNCs prepared by the acid-free and dialysis-free process exhibited higher mass recovery ratios, significantly higher amounts of surface anionic groups, and smaller and more homogeneous widths.

Controlled release of carvacrol and curcumin: bio-based food packaging by synergism action of TEMPO-oxidized cellulose nanocrystals and cyclodextrin

Oxidized cellulose nanocrystals with sodium carboxylate groups (TOCNC-COONa) and with free carboxyl groups (TOCN-COOH) were prepared and then chemically modified with beta-cyclodextrin (βCD) and hydroxypropyl-beta-cyclodextrin (HPβCD) to prepare materials able to load and release antibacterial molecules over a prolonged period of time. The materials were characterized by infrared spectroscopy, and the CD content of modified TOCNCs determined by phenolphthalein colorimetry. The extent of grafting was also assessed by QCM-D and microscopy was used to ascertain and compare the morphology of both TOCNC-COONa/HPβCD and TOCNC-COOH/HPβCD. Then, carvacrol and curcumin were entrapped by the attached HPβCD and their prolonged release confirmed, as compared to neat material. The combined effects of HPβCD and carvacrol on the antimicrobial properties of TOCNC-COOH films were finally evaluated.