Click chemistry modifications for the selective crosslinking of wood pulp fibers - effect on the physical and mechanical properties of paper

The Cu(i)-catalyzed Huisgen cycloaddition click chemistry reaction is of particular interest in the production of paper sheets or natural fiber composites since it leads to the formation of chemically stable bonds between two fibers. This study focuses on the click chemistry modification of kraft pulp fibers. We based our approach on prior research that treated kraft fibers using click chemistry, including propargylation and tosylation reactions. Our focus was on enhancing these treatments to achieve better final sheet properties. After the azidation of tosylated fibers, the crosslinking is carried out with and without a catalyst using water as a solvent to form enhanced kraft fiber sheets. The chemical characterization and the mechanical properties of fibers obtained at intermediate stages confirmed the presence of various functions on the surface of the modified fibers, with a very high degree of substitution and the inter-fiber cross-linking by click chemistry. The presence of inter-fibers covalent bonds led to significant improvements in the mechanical strength and tensile stiffness of the sheets.

Low carbon footprint preparation of MXene incorporated lignocellulosic fibers for high thermal conductivity applications

New wood-based composite materials with thermal conductivity are greatly desired in the fields of packaging materials for electronic components. In this study, a new multifunctional composite material (M@FC) is prepared by simply blending clay-like Ti₃C₂T_x MXene and delignified wood fibers together, and then followed by an infusing epoxy resin with environmentally friendly vacuum assisted resin transfer molding (VARTM) process. The resulting M@FC (0.92 W m^-1 K^-1) possesses superior thermal conductivity as compared to natural wood (0.099 W m^-1 K^-1) and most polymers. Furthermore, after the VARTM process, the structure of the M@FC is tighter, and thus showing excellent mechanical properties (tensile strength of 93.0 MPa and flexural strength of 172.7 MPa). In addition, good water resistance and excellent flame retardant property are observed for M@FC. The improvement of thermal conductivity provides the possibility for its application for packaging materials in electronic components. This study using waste wood as the important component provides a new idea for carbon cycling and recycling of natural resources.

Latent, Cross-Linkable Triazole Platform on a Carbon Fiber Surface for Enhancing Interfacial Cross-Linking within Carbon Fiber/Epoxy Composites

A long-running need in carbon fiber composite production is to ameliorate interfacial adhesion between the polymer and carbon fibers. Here, we present a convenient and feasible strategy for controlling the carbon fiber's surface in a continuous process: syntheses of click-modified silanes via copper(I)-catalyzed azide-alkyne cycloaddition reaction and grafting them onto fiber surfaces which prepare a latent curable platform under mild processes without postmodification. As 1,2,3-triazole moieties from the click reaction were added to the epoxy/dicyandiamide system, they triggered additional reactions in the later conversion stage; approximately, a 20% increase in the total reaction enthalpy compared to the system with no additives was obtained. We expected the enhanced cross-linking between the surface and matrix to expand the interfacial area, leading to reinforcements on interfacial adhesion and stress-transfer abilities within composites. The merit of the approach is well-demonstrated by conductive atomic force microscopy, showing that the interphase can be extended up to 6-fold when the triazole platform acts as curatives and serve as bridges after the epoxy cure. Consequently, the composite's interfacial shear strength and interlaminar shear strength were increased up to 78 and 72%, respectively. This work affords a reactive platform where a custom-tailored fiber/matrix interface can be designed by virtue of versatility in clickable reactants.

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.

Highly Norbornylated Cellulose and Its "Click" Modification by an Inverse-Electron Demand Diels-Alder (iEDDA) Reaction

A facile, catalyst-free synthesis of a norbornylated cellulosic material (NC) with a high degree of substitution (2.9) is presented by direct reaction of trimethylsilyl cellulose with norbornene acid chloride. The resulting NC is highly soluble in organic solvents and its reactive double bonds were exploited for the copper-free inverse-electron demand Diels–Alder (iEDDA) “click” reaction with 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine. Reaction kinetics are comparable to the well-known Huisgen type 1,3-dipolar cycloaddition of azide with alkynes, while avoiding toxic catalysts.

Molecularly imprinted polymer-based photocatalyst for highly selective degradation of methylene blue

ZnO quantum dots were synthesized by chemical precipitation, CuFe₂O₄ nanoparticles were prepared by in situ synthesis of cellulose, and then ZnO/CuFe₂O₄ (ZCF) composites were fabricated. A photocatalyst (ZCF@MB-MIP) with specific molecule recognition and photocatalytic degradation characteristics was then produced by a surface imprinting method using methylene blue (MB) as the template molecule. The structure of ZCF@MB-MIP was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and X-ray diffraction. The photocatalytic efficiency of ZCF@MB-MIP and its specific recognition performance in MB degradation was analyzed. The adsorption kinetics of MB by ZCF@MB-MIP conformed to the quasi-secondary adsorption kinetics model. ZCF@MB-MIP displayed effective photocatalytic degradation of MB under natural light. The degradation rate reached 95.8%, which was much higher than those of ZCF, CuFe₂O₄ nanoparticles, and a non-imprinted reference sample under the same conditions. This work is a useful reference for the construction of photocatalysts that show highly selective recognition of dye molecules.

Preparation of a Novel Cellulose-Styrene Copolymer Adsorbent and Its Adsorption of Nitrobenzene from Aqueous Solutions

A novel cellulose–styrene copolymer adsorbent (cellulose-St) was prepared using free radical polymerization. Successful polymerization was confirmed through Fourier Transform Infrared Spectroscopy (FTIR), Carbon 13 Solid Nuclear Magnetic Resonance (¹³C NMR) Spectroscopy, Scanning Electron Microscopy (SEM), etc. Cellulose-St possessed good hydrophobicity, and the best water contact angle of cellulose-St samples could reach 146°. It had the ability of adsorption for nitrobenzene (NB), and the adsorption process could be well described by the pseudo-second-order (R² > 0.99) and three-stage intraparticle diffusion (R² > 0.99) kinetic models. Furthermore, the dynamic adsorption experiments revealed that cellulose-St had the potential for continuous separation of NB in water, and the breakthrough point for the initial NB concentration of 10 mg/L reached 1.275 L/g. Moreover, cellulose-St exhibited excellent environmental adaptability that it could maintain its hydrophobicity and adsorption ability for NB in strong acids, strong alkalis, or organic solvents. The used cellulose-St could be reused after washing with ethanol and keep almost constant adsorption capacity after ten cycles.

Hydrophobic functionalization reactions of structured cellulose nanomaterials: Mechanisms, kinetics and in silico multi-scale models

Nanoscale-interfaced cellulose nanomaterials are extracted from polysaccharides, which are widely available in nature, biocompatible and biodegradable. Moreover, the latter have a potential to be recycled, upcycled, and formulate therefore a great theoretical predisposition to be used in a number of applications. Nanocrystals, nano-fibrils and nanofibers possess reactive functional groups that enable hydrophobic surface modifications. Analysed literature data, concerning mechanisms, pathways and kinetics, was screened, compared and assessed with regard to the demand of a catalyst, different measurement conditions and added molecule reactions. There is presently only a scarce technique description for carbonOH bond functionalization, considering the elementary chemical steps, sequences and intermediates of these (non)catalytic transformations. The overview of the prevailing basic research together with in silico modelling approach methodology gives us a deeper physical understanding of processes. Finally, to further highlight the applicability of such raw materials, the review of the development in several multidisciplinary fields was presented.

Grafting Diels-Alder moieties on cellulose nanocrystals through carbamation

The Diels-Alder reaction is a promising click chemistry for the design of advanced materials from cellulose nanocrystals (CNCs). Transferring such chemistry to cellulose nanocrystals requires the precise grafting of reactive Diels-Alder moeities under heterogeneous conditions without compromising the nanocrystals morphology. In this study toluene diisocyanate is used as a spacer to graft Diels-Alder moieties viz the furyl and protected maleimido moieties onto cellulose nanocrystals. A factorial experimental design reveals that reaction time and reactant molar ratio positively affect the grafting efficiency, as evidenced by FTIR and CHNS elemental analysis. The surface degree of substitution was analyzed via CHNS elemental analysis and XPS and found to range between 0.05 to 0.30, with a good agreement between the two techniques. ¹³C CP/MAS NMR confirmed that the grafted moieties and CNCs are intact after reaction. Side reactions were also observed and their impact on performing controllable click chemistry between cellulose nanocrystals is discussed.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Hydrophobization of Cellulose Nanocrystals for Aqueous Colloidal Suspensions and Gels

Surface hydrophobization of cellulose nanomaterials has been used in the development of nanofiller-reinforced polymer composites and formulations based on Pickering emulsions. Despite the well-known effect of hydrophobic domains on self-assembly or association of water-soluble polymer amphiphiles, very few studies have addressed the behavior of hydrophobized cellulose nanomaterials in aqueous media. In this study, we investigate the properties of hydrophobized cellulose nanocrystals (CNCs) and their self-assembly and amphiphilic properties in suspensions and gels. CNCs of different hydrophobicity were synthesized from sulfated CNCs by coupling primary alkylamines of different alkyl chain lengths (6, 8, and 12 carbon atoms). The synthetic route permitted the retention of surface charge, ensuring good colloidal stability of hydrophobized CNCs in aqueous suspensions. We compare surface properties (surface charge, ζ potential), hydrophobicity (water contact angle, microenvironment probing using pyrene fluorescence emission), and surface activity (tensiometry) of different hydrophobized CNCs and hydrophilic CNCs. Association of hydrophobized CNCs driven by hydrophobic effects is confirmed by X-ray scattering (SAXS) and autofluorescent spectroscopy experiments. As a result of CNC association, CNC suspensions/gels can be produced with a wide range of rheological properties depending on the hydrophobic/hydrophilic balance. In particular, sol-gel transitions for hydrophobized CNCs occur at lower concentrations than hydrophilic CNCs, and more robust gels are formed by hydrophobized CNCs. Our work illustrates that amphiphilic CNCs can complement associative polymers as modifiers of rheological properties of water-based systems.

Fabrication of Microcapsules by the Combination of Biomass Porous Carbon and Polydopamine for Dual Self-Healing Hydrogels

Artificial development of smart materials from agricultural waste or food residues is particularly desirable for green chemistry. In this paper, dual-network self-healing hydrogels were successfully fabricated by using functional microcapsules. These microcapsules were established by biomass porous carbon (PC) after recycling of apple residues. Glutaraldehyde (GA) as the healing agent was embedded in the porous carbon, and the outer surface was coated with polydopamine (PDA). After the microcapsules were added, modifying guar gum-type hydrogels were successfully obtained with dual self-healing performance by the combination of a healing agent and metal-ligand coordination. The self-healing efficiency was about 89.9% from the tension test, and the fracture strength was measured as 7.68 MPa. These results not only highlight a new idea for the utilization of apple residues but also provide a new method for the preparation of excellent self-healing hydrogels.

Amidoxime-modified chitosan for pigment red 224 enrichment through reversible assembly

An amidoxime-modified chitosan, featuring favorable porosity and super-lipophilic properties, was successfully prepared for pigment red 224 enrichment.

Polymer Nanocomposites via Click Chemistry Reactions

The emerging areas of polymer nanocomposites, as some are already in use in industrial applications and daily commodities, have the potential of offering new technologies with all manner of prominent capabilities. The incorporation of nanomaterials into polymeric matrix provides significant improvements, such as higher mechanical, thermal or electrical properties. In these materials, interface/interphase of components play a crucial role bringing additional features on the resulting nanocomposites. Among the various preparation strategies of such materials, an appealing strategy relies on the use of click chemistry concept as a multi-purpose toolbox for both fabrication and modulation of the material characteristics. This review aims to deliver new insights to the researchers of the field by noticing effective click chemistry-based methodologies on the preparation of polymer nanocomposites and their key applications such as optic, biomedical, coatings and sensor.

Hydrogels for Biomedical Applications: Cellulose, Chitosan, and Protein/Peptide Derivatives

Hydrogels based on polysaccharide and protein natural polymers are of great interest in biomedical applications and more specifically for tissue regeneration and drug delivery. Cellulose, chitosan (a chitin derivative), and collagen are probably the most important components since they are the most abundant natural polymers on earth (cellulose and chitin) and in the human body (collagen). Peptides also merit attention because their self-assembling properties mimic the proteins that are present in the extracellular matrix. The present review is mainly focused on explaining the recent advances on hydrogels derived from the indicated polymers or their combinations. Attention has also been paid to the development of hydrogels for innovative biomedical uses. Therefore, smart materials displaying stimuli responsiveness and having shape memory properties are considered. The use of micro- and nanogels for drug delivery applications is also discussed, as well as the high potential of protein-based hydrogels in the production of bioactive matrices with recognition ability (molecular imprinting). Finally, mention is also given to the development of 3D bioprinting technologies.

"Click" on Alkynylated Carbon Quantum Dots: An Efficient Surface Functionalization for Specific Biosensing and Bioimaging

Surface functionalization is an essential pre requisite for wide and specific applications of nanoparticles such as photoluminescent (PL) carbon quantum dots (CQDs), but it remains a major challenge. In this report, alkynylated CQDs, prepared from carboxyl-rich CQDs through amidation with propargylamine in the presence of 1,1'-carbonyldiimidazole, were modified efficiently with azido molecular beacon DNA through a copper(I)-catalyzed alkyne-azide cycloaddition reaction (CuAAC). As a proof-of-concept, the DNA-modified CQDs are then bonded with gold nanoparticles (AuNPs, 5 nm) through a gold-sulfur bond. Owing to the emission enhancement, this complex can then be applied to the recognition of a single-base- mismatched target. The same functionalizing strategy applied to click the alkynylated CQDs with a nuclear localization sequence (NLS) peptide showed that the NLS-modified CQDs could target the nuclei specifically. These results indicate that surface functionalization of CQDs through a nonstoichiometric copper chalcogenide nanocrystal- (nsCuCNC-) catalyzed click reaction is efficient, and has significant potential in the fields of biosensing and bioimaging.

Ionic Compatibilization of Cellulose Nanocrystals with Quaternary Ammonium Salt and Their Melt Extrusion with Polypropylene

On account to their high mechanical properties along with high reinforcing capacity, cellulose nanocrystals (CNCs) could be the ultimate choice for polymer nanocomposites as filler. Recently, different strategies have been investigated for the melt extrusion of CNC-based polymer nanocomposites because it is a solvent-free process and because this technique is more viable for commercial industrialization. However, most thermoplastic polymers are processed at high temperatures, and sulfuric acid preparation of CNC limits the processing because of surface sulfate groups degradation. In this study we profitably used these negatively charged groups, and quaternary ammonium salt was ionically adsorbed on CNC by a simple aqueous method. Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction were used to characterize adsorbed CNC, and changes in polarity were investigated by contact angle measurements. Modified CNC was extruded with polypropylene at 190 °C, and the ensuing composites were characterized in terms of mechanical (by dynamic mechanical analysis and tensile tests), thermal (by differential scanning calorimetry), and morphological (scanning electron microscopy) properties. The melt rheology of PP-based nanocomposites was also reported.

Nanocellulose, a tiny fiber with huge applications

Nanocellulose is of increasing interest for a range of applications relevant to the fields of material science and biomedical engineering due to its renewable nature, anisotropic shape, excellent mechanical properties, good biocompatibility, tailorable surface chemistry, and interesting optical properties. We discuss the main areas of nanocellulose research: photonics, films and foams, surface modifications, nanocomposites, and medical devices. These tiny nanocellulose fibers have huge potential in many applications, from flexible optoelectronics to scaffolds for tissue regeneration. We hope to impart the readers with some of the excitement that currently surrounds nanocellulose research, which arises from the green nature of the particles, their fascinating physical and chemical properties, and the diversity of applications that can be impacted by this material.