Functionalized Cellulose Nanocrystals Research Articles

Dye Removal Using Sustainable Membrane Adsorbents Produced from Melamine Formaldehyde−Cellulose Nanocrystals and Hard Wood Pulp

Melamine formaldehyde (MF)-functionalized cellulose nanocrystals (CNC) prepared via an in situ polycondensation reaction were incorporated into hardwood pulp (HWP) membrane filters to remove anioni...

Facile One-step Fabrication of Functional Cellulose Nanocrystals with High Efficiency under Microwave-ultrasound Synergy

The use of cellulosic biomass for the manufacture of functional cellulose nanocrystals (FCNs) in a mild and green process is limited due to the multiple hydrogen bonds between cellulose. Based on the mechanochemical mechanism, an efficient and green approach to cleave hydrogen bonds and fabricate FCNs was realized via microwave-ultrasound synergy. In the one-step process, impact force, crash force, friction, chemical action, and thermodynamic interaction combined to create synergistic effects, accelerating the cleavage of hydrogen bonds and formation of FCNs synchronously. One-step purification of FCNs was implemented after reaction for the recovery of byproducts, which was critical to cost reduction and waste liquor treatment. FCNs with high crystallinity of 80%, high charge density, and good dispersion stability were obtained. Thus, a facile versatile green avenue for the large-scale production of FCNs was achieved in the study, and is expected to carry significant benefits in terms of economy and sustainability.

Functional cellulose nanocrystals containing cationic and thermo-responsive polymer brushes

Cationic and thermo-responsive polymer brushes were grafted from the surface of cellulose nanocrystals. Di(ethylene glycol) methyl ether methacrylate (MEO2MA) and poly(oligoethylene glycol) methyl ether acrylate (OEGMA300) and (2-methacryloyloxyethyl) trimethylammonium chloride (DMC) were grafted from cellulose nanocrystals (CNCs) via free radical polymerization. The CNC-g-POEGMA (CP) possessed a tunable lower critical solution temperature (LCST) of about 50 °C, and cloud point measurements confirmed that the LCST of the nanoparticles could be manipulated within the range of 40−47 °C by adjusting the DMC content. The salt effect was also investigated, and the results revealed a typical salting-out effect for the CNC-g-POEGMA after the introduction of KCl. On the other hand, the CNC-g-POEGMA-g-DMC (CPD) copolymers displayed two salt-responsive characteristics; polyelectrolyte effect at lower salt concentrations, followed by the salting-out effect at higher salt concentrations, which is dependent on the DMC content.

Effect of the Incorporation of Functionalized Cellulose Nanocrystals into UiO‐66 on Composite Porosity and Surface Heterogeneity Alterations

AbstractNew composites consisting of 2% cellulose nanocrystals (NC) of various surface chemistries (i.e., carboxylic acids, sulfonic acids, and amines) incorporated into UiO‐66 are synthesized. Nanocellulose and the composites are characterized by X‐ray diffraction, Fourier‐transform infrared spectroscopy, N2 and CO2 adsorption, and thermogravimetric analysis. The analyses reveal information about the crystallinity, pore structure, and thermal stability of the composites. The results show a marked development of microporosity (≈30%), which is linked mainly to the formation of a NC/UiO‐66 interface, to disturbances in the UiO‐66 nucleation process, and to missing cluster defects. The latter is related to the geometrical constraints of metal–organic framework (MOF) crystallization around the NC nuclei. Pore size distributions do not depend markedly on the chemistry of NC. While pores in the composites with sizes <0.5 nm are associated with the involvement of NC functional groups in the formation of MOF units, the pores with sizes >1.1 nm have their origin likely in missing linkers and missing clusters. Moreover, the surface chemistry of NC and that of the interface affects the amount of CO2 adsorbed and the strength of adsorption.

Surfactant-Free Latex Nanocomposites Stabilized and Reinforced by Hydrophobically Functionalized Cellulose Nanocrystals

Stable poly(styrene-co-2-ethylhexyl acrylate) latex particles with diameter less than 600 nm were prepared by the miniemulsion polymerization of Pickering emulsions stabilized with hexyl-functionalized cellulose nanocrystals (CNC-hexyl-COOHs). Polymer nanocomposites were fabricated by casting of the CNC-stabilized latex particles, and the thermomechanical properties and microstructures of the films were studied and related to the type and amount of stabilizer as well as the processing conditions. Compared to the latex films stabilized with low-molecular-weight sodium dodecyl sulfate (SDS) surfactant, or using a combination of SDS and carboxylic acid CNC-COOHs, films stabilized solely with the alkyl-functionalized CNC-hexyl-COOHs showed much higher storage moduli in the rubbery regime and lower water uptake. Scanning electron microscopy (SEM) revealed a CNC network structure that is formed by excluded volume effects of the latex particles, which concentrates the CNC-hexyl-COOHs into the interstitial space during solvent evaporation. This effect results in the formation of a percolation network at a lower CNC concentration within the latex composite films. The network can be further reinforced by increasing the concentration of CNCs through an “ex situ” process where CNC-hexyl-COOH-stabilized latex particles were mixed with CNC-COOH aqueous dispersions before film casting. The ability to replace low-molecular-weight surfactants in water-based latexes with alkyl-functionalized CNCs that are not only biosourced but also act as reinforcing agents offers an opportunity to expand the property profile of a variety of commercial products such as paints, coatings, and adhesives.

Functionalized cellulose nanocrystals as the performance regulators of poly(β-hydroxybutyrate-co-valerate) biocomposites

To investigate the relationship between functional groups on cellulose nanocrystals (CNC) and the performance of poly(β-hydroxybutyrate-co-valerate) (PHBV), the surface of CNC was modified by surface graft modification and PHBV/CNC biocomposites were prepared by melt blending. To demonstrate the interfacial adhesion difference between hydrophobic PHBV and hydrophilic CNC, palmitoyl chloride and ε-caprolactone had been used to tailor the oleophilic property of CNC. Results showed that CNC had heterogeneous nucleation effect on the crystallization process of PHBV, while the entanglement of molecular chains weakened the promoting functions of CNC-g-C16 (CNC grafted with palmitoyl chloride) and CNC-g-CL (CNC grafted with ε-caprolactone). Furthermore, CNC-g-CL exhibited better interfacial adhesion with PHBV when compared with CNC-g-C16. And 1 wt% CNC-g-CL improved the tensile strength of PHBV biocomposite to 38.09 MPa, which is 26.25% higher than PHBV.

Functionalization of Cellulose Nanocrystals with POEGMA Copolymers via Copper-Catalyzed Azide-Alkyne Cycloaddition for Potential Drug-Delivery Applications.

Elongated colloidal nanoparticles (NPs) have significant potential for drug delivery and imaging applications in cancer therapy, but progress depends on developing a deeper understanding of how their physicochemical properties affect their interactions with cells and with tumors. Cellulose nanocrystals (CNCs) are biocompatible, rodlike colloids that are broadly surface-functionalizable, making them interesting as modular drug carriers. In this report, we describe the attachment of a statistical copolymer containing oligoethylene glycol methacrylate (OEGMA; Mn ≈ 500 Da) and small amounts of aminopropylmethacrylamide (APMA) to CNCs. Here, the copolymer is designed to serve as a "stealth" corona to minimize protein adsorption, and the amino groups provide functionality for the attachment of diagnostic or therapeutic moieties. The corona polymer with a terminal azide group was synthesized by atom transfer radical polymerization using tert-butyloxycarbonyl (tBoc)-protected APMA as the comonomer. A key step in this synthesis was the grafting of acetylene groups to the CNC surface via a reaction with NaOH plus propargyl bromide in aqueous dimethyl sulfoxide. The copolymer was attached to the CNCs using copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry. By determining the mean number of amino groups per copolymer and amino group content of the CNC sample, we were able to infer that there were on average ca. 300 polymer molecules per CNC. Preliminary evaluation in a human ovarian cancer cell line (HEYA8) and a human breast cancer cell line (MDA-MB-436) demonstrated that these CNCs are nontoxic. We also assessed the cellular uptake of these CNC NPs in the same two cell lines using flow cytometry and distinguished between NPs being internalized by the cell or surface-bound using a trypan blue quenching experiment. These results provide support for applications of polymer-coated CNCs in medicine and are encouraging for further studies in vitro and in vivo to evaluate their potential as drug-delivery vehicles.

Fabricating robust soft-hard network of self-healable polyvinyl alcohol composite films with functionalized cellulose nanocrystals

In this study, conductive cellulose nanocrystals (CNCs) were coated with polypyrrole (PPy) using in situ chemical polymerization to form CNC-PPy conductive nano-network. The one-pot polymerization of “hard” segment methyl methacrylate (MMA) was continued onto above functionalized CNCs, then blended with “soft” molecular segment polyvinyl alcohol (PVA) to contain self-healing and conductive composite film (CPMV) fabricated by soft-hard network. In addition, the tensile strength of CPMV films with 2 wt% CNC-PPy was enhanced by 47.1%. Also, CPMV films exhibited self-healing properties due to the presence of hydrogen bonding dynamic network and showed sensitive resistance changes under external stimuli, which could be used to monitor various actions of the human body. Thus, the CPMV films present potential applications in electronic devices such as flexible electrodes, biosensors, and implantable devices.

Enhanced functional properties of nanocomposite film incorporated with EGCG-loaded dialdehyde glucomannan/gelatin matrix for food packaging

The development of konjac glucomannan (KGM) based films for use in food packaging has aroused increasing attention due to biodegradability, compatibility, and availability. Epigallocatechin gallate (EGCG) loaded dialdehyde glucomannan (DG) was incorporated into a gelatin (G) solution to improve the functional properties of DGG film. Rutin functionalized cellulose nanocrystal (RCNC) was incorporated into a DG/G matrix (DGG). The influences of RCNC addition on the structural, mechanical properties, barrier and optical properties were investigated. The RCNC@DGG films were prepared by the solvent casting method. The surface morphology of the RCNC@DGG films were analyzed by SEM and AFM. The crystal structure and thermal ability of the film were investigated by XRD and TGA-DTG. Elemental and characteristic peak changes were evaluated by FT-IR. The microstructure of the films showed that the introduced RCNC appeared to be dispersed within the DGG matrix, thereby decreasing the free volume, and enhancing RCNC@DGG films' mechanical and barrier properties. Compared with DGG film, RCNC@DGG nanocomposite films showed excellent antibacterial activity against food-borne pathogens, due to the antibacterial property of the EGCG. Therefore, RCNC@DGG nanocomposite films showed the potential for applications in active food packaging materials.

Enhanced water uptake of PHBV scaffolds with functionalized cellulose nanocrystals

Super hydrophilic scaffolds of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with 3 wt % of acetylated (CNC-Ac) and PEGylated (CNC-PEG) cellulose nanocrystals (CNC) were prepared. PHBV, PHBV/CNC-Ac, and PHBV/CNC-PEG scaffolds were characterized with respect to their morphology by scanning electron microscopy (SEM) and X-ray microtomography. The crystallinity was evaluated by differential scanning calorimetry (DSC) and the mechanical properties by uniaxial compression tests. The presence of residual solvent was identified by gas chromatography (GC), wettability measured by static contact angle and aqueous adsorption by gravimetry. All the scaffolds showed porous morphology, being that, for neat PHBV the morphology was more regular with oriented pores. The porosity was reduced by 26% with the introduction of CNC-Ac and CNC-PEG, and the compression modulus increased by 25% and 72% for PHBV/CNC-Ac and PHBV/CNC-PEG scaffolds, respectively, compared to neat PHBV. Even with lower porosities, PHBV/CNC-Ac and PHBV/CNC-PEG adsorbed 16% and 67% more water than PHBV scaffold, following the intraparticle diffusion model for all the samples. No residual solvents were found and the crystallinity was slightly increased upon addition of CNC-Ac and CNC-PEG. Therefore, the addition of CNC-Ac and CNC-PEG can improve both compressive modulus and water uptake, turning PHBV nanocomposite scaffolds suitable for tissue engineering applications.

Comprehensive Insight into Degradation Mechanism of Green Biopolyester Nanocomposites Using Functionalized Cellulose Nanocrystals

Cellulose nanoparticles (CNPs) have been widely reported to improve the crystallization rate, mechanical and thermal properties, as well as degradation behavior of poly(3-hydroxybutyrate-co-3-hydro...

Functionalizing Cellulose Nanocrystals with Click Modifiable Carbohydrate-Binding Modules.

Functionalized cellulose nanocrystals (CNC) have unique properties that make them attractive in various applications such as drug delivery, hydrogels, and emulsions. However, the predominant chemical methods currently used to functionalize cellulose nanocrystals have a large environmental footprint. Although greener methods are desirable, the relatively inert nature of cellulose crystals presents a major challenge to their potential modification in aqueous media. In the work reported here, carbohydrate binding modules (CBMs) were used to introduce new functionality to cellulose surfaces. CBM2a, which has a strong affinity for crystalline cellulose, was functionalized with an alkyne at the terminal amine position. The alkyne group, which was introduced onto the cellulose surface with CBM2a, underwent a Click reaction with polyethylene glycol (PEG) to modify CNC surfaces. This provided a strong, non-covalent modification of cellulose surfaces that was carried out in a one-pot reaction in aqueous media. The CBM-PEG modification of cellulose surfaces increased CNC redispersion after drying and improved suspension stability based on steric interactions. It was apparent that hybrid polysaccharide-protein, self-assembled nanoparticles could be effectively produced, with potential for nanomedicine, immunoassay, and drug delivery applications.

Tailored and Integrated Production of Functional Cellulose Nanocrystals and Cellulose Nanofibrils via Sustainable Formic Acid Hydrolysis: Kinetic Study and Characterization

Cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are of great interest to researchers due to their outstanding properties and wide application potentials. However, green and sustainab...

Optimized anti-biofouling performance of bactericides/cellulose nanocrystals composites modified PVDF ultrafiltration membrane for micro-polluted source water purification.

The covalently functionalized cellulose nanocrystal (CNC) composites were synthesized by bonding common bactericides, such as dodecyl dimethyl benzyl ammonium chloride (DDBAC), ZnO and graphene oxide (GO) nanosheets, onto the CNC's surface. Then, the DDBAC/CNC, ZnO/CNC and GO/CNC nanocomposites modified polyvinylidene fluoride (PVDF) ultrafiltration membranes were fabricated by a simple one-step non-solvent induced phase separation (NIPS) process. The resultant hybrid membranes possessed porous and rough surfaces with more finger-like macropores that even extended through the entire cross-section. The hydrophilicity, permeability, antibacterial and antifouling performance and mechanism of the hybrid ultrafiltration membranes were evaluated and compared in detail, aiming at screening a superior hybrid membrane for practical application in micro-polluted source water purification. Among these newly-developed hybrid membranes, GO/CNC/PVDF exhibited an enhanced perm-selectivity with a water flux of 230 L/(m2 h bar) and humic acid rejection of 92%, the improved antibacterial activity (bacteriostasis rate of 93%) and antifouling performance (flux recovery rate (FRR) of >90%) being due to the optimized pore structure, higher surface roughness, incremental hydrophilicity and electronegativity. A lower biofouling level after three weeks' filtration of the actual micro-polluted source water further demonstrated that embedding the hydrophilic and antibacterial GO/CNC nanocomposite into the polymer matrix is an effective strategy to improve membrane anti-biofouling ability.

Functionalization of cellulose nanocrystals with γ-MPS and its effect on the adhesive behavior of acrylic pressure sensitive adhesives

In this work, functionalized cellulose nanocrystal (fCNC) was obtained by the grafting of 3-methacryloxypropyltrimethoxysilane coupling agent (γ-MPS) onto CNC. Then acrylic pressure sensitive adhesive (PSA) incorporated with various contents of CNC or fCNC was successfully synthesized by an in-situ emulsion polymerization, and the effects of CNC or fCNC on the sol molecular weight, latex properties, thermal properties, viscoelastic properties, and adhesive performance of the acrylic PSA were investigated. The results illustrated a coinstantaneous improvement of tack, shear strength and peel strength with increasing the loading of both CNC and fCNC. Interestingly, fCNC showed much more improvement than CNC on adhesive performance of acrylic PSA. The fCNC-1/acrylic PSA showed tack of 27#, shear strength of 70 h, and peel strength of 13.4 N/25mm, which were 12.5%, 4%, and 106% higher than those of CNC-1/acrylic PSA and 35%, 100%, and 163% higher than those of neat acrylic PSA, respectively. The superior adhesive performance of the fCNC/acrylic PSA films was supposed to be attributed to better compatibility and dispersion of fCNC in the acrylic copolymer. Thus, this work presents a feasible strategy for utilization of CNC in adhesives and coatings.

High-Yield Synthesis of Functionalized Cellulose Nanocrystals for Nano-Biocomposites

A facile versatile green one-step procedure to fabricating functionalized cellulose nanocrystals (CNCs) with high yields and thermostability was put forward via molten oxalic acid hydrolysis by aid of simultaneous microwave and sonication. The synchronized hydrolysis and esterification of cellulose took place in the one-pot solvent-free reaction, and thus we developed an environmentally benign and scalable concurrent acid hydrolysis/Fischer esterification method to produce acid-functionalized CNCs using microwave and sonication in 85.5% yield. Compared to classical methods for the functionalization of CNCs, the presented study avoided the extensive consumption of water and solvent and achieved zero waste liquid discharge. Moreover, the used solid acid could easily be recycled to make it possible for the large-scale and cleaner production of CNCs. The resultant CNCs with high thermal stability and excellent dispersion stability are excellent for nano-biocomposite applications.

A novel nanocomposite membrane containing modified cellulose nanocrystals for copper ion removal and dye adsorption from water

The aim of this study was developing novel membranes based on polyethersulfone (PES) as matrix and amine functionalized cellulose nanocrystals (CNC) as nanofiller for copper ion and direct red-16 removal from water. The surface modification of CNC was performed using (3-aminopropyl)triethoxysilane (APTES) and confirmed by Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy. Then, PES membranes were prepared by embedding various concentrations (0, 0.1, 0.5, and 1 wt%) of modified CNC (MCNC). The results showed that the maximum adsorption capacity of copper ions was 90% for membranes containing 1 wt% MCNC. Dye removal percentage was 89% for neat PES and increased to 99% for 1 wt% MCNC loading. The outcomes of this study demonstrated that incorporating this type of modified CNC in PES membranes improved the efficacy of impurities removal from water and can be suggested as a simple technique for water filtration.

Cross-linked cellulose nanocrystal aerogels as viable bone tissue scaffolds

Chemically cross-linked cellulose nanocrystal (CNC) aerogels possess many properties beneficial for bone tissue scaffolding applications. CNCs were extracted using sulfuric acid or phosphoric acid, to produce CNCs with sulfate and phosphate half-ester surface groups, respectively. Hydrazone cross-linked aerogels fabricated from the two types of CNCs were investigated using scanning electron microscopy, X-ray micro-computed tomography, X-ray photoelectron spectroscopy, nitrogen sorption isotherms, and compression testing. CNC aerogels were evaluatedin vitrowith osteoblast-like Saos-2 cells and showed an increase in cell metabolism up to 7 days while alkaline phosphatase assays revealed that cells maintained their phenotype. All aerogels demonstrated hydroxyapatite growth over 14 days while submerged in simulated body fluid solution with a 0.1 M CaCl2 pre-treatment. Sulfated CNC aerogels slightly outperformed phosphated CNC aerogels in terms of compressive strength and long-term stability in liquid environments, and were implanted into the calvarian bone of adult male Long Evans rats. Compared to controls at 3 and 12 week time points, sulfated CNC aerogels showed increased bone volume fraction of 33% and 50%, respectively, compared to controls, and evidence of osteoconductivity. These results demonstrate that cross-linked CNC aerogels are flexible, porous and effectively facilitate bone growth after they are implanted in bone defects. Statement of SignificanceDue to the potential complications associated with autografts, there is a need for synthetic bone tissue scaffolds. Here, we report a new naturally-based aerogel material for bone regeneration made solely from chemically cross-linked cellulose nanocrystals (CNC). These highly porous CNC aerogels were shown to promote the proliferation of bone-like cells and support the growth of hydroxyapatite on their surface in vitro. The first in vivo study on these materials was conducted in rats and showed their osteconductive properties and an increase in bone volume up to 50% compared to sham sites. This study demonstrates the potential of using functionalized cellulose nanocrystals as the basis for aerogel scaffolds for bone tissue engineering.

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.

Mechanisms of the immune response cause by cationic and anionic surface functionalized cellulose nanocrystals using cell-based assays

The interest in functionalized cellulose nanocrystals (CNCs) for multiple biomedical application has been increasing in recent years. CNCs are suitable to functionalization with an array of polymers, generating chemically related nanomaterials with different morphologies, surface charges that can affect bioreactivity, including immune response. In this study, we sought to understand the mechanistic differences regarding immunological responses evoked by functionalized CNCs and whether surface charges play a role in this effect. We investigated the effect of a cationic, CNCs-poly(APMA), and an anionic, CNCs-poly(NIPAAm) derivatives on the secretion of inflammatory cytokines, mitochondria-derived ROS and mitochondrial function and antioxidant response as well as on endoplasmic reticulum (ER) stress, in human and murine inflammatory cells. The cationic CNCs-poly(APMA) evoked a more robust immunological response in murine cell line, while the anionic CNCs-poly(NIPAAm) showed a significant NLRP3 inflammasome-dependent and independent immunological response in human monocytes. Moreover, CNCs-poly(NIPAAm) induced greater formation of acidic vesicular organelles, mitochondrial ROS in non-stimulated cells while CNCs-poly(APMA) mainly affected mitochondrial function by decreasing the intracellular ATP. The differences on the biological responses may be related to the surface charges of CNCs, and their likely interactions with intra and extracellular biomolecules.