Reactive template method for synthesis of water-soluble fluorescent silver nanoclusters supported on the surface of cellulose nanofibers.

The effect of cellulose nanofibers (CNFs) and poly [methyl methacrylate (MMA)]-grafted cellulose nanofibers (CNF-g-PMMA) on mechanical properties and degradability of a 75/25 low density polyethylene/thermoplastic starch (LDPE/TPS) blend was investigated. Graft copolymerization on CNFs was performed in an aqueous suspension by free radical polymerization using MMA as an acrylic monomer. In addition, a LDPE/TPS blend was reinforced by different amounts of CNFs (1–5 wt%) and CNF-g-PMMA (1–7 wt%) using a twin-screw extruder. A 61% grafting of PMMA on the surface of CNFs was demonstrated by gravimetric analysis. Moreover, after modification the X-ray photoelectron spectroscopy analysis showed a 20% increase of carbon atoms on the surface of CNFs and a 22.6% decrease in the oxygen content of its surface. The mechanical properties of the CNFs-modified composites were significantly improved compared to the unmodified nanocomposites. The highest tensile strength and Young’s modulus were obtained for the composites reinforced by 3 and 7 wt% CNF-g-PMMA, respectively. The degradability of cellulose nanocomposites was studied by water absorption and soil burial tests. Surface modification of CNFs lowered water absorption, and soil burial test of the LDPE/TPS blend showed improvement in biodegradability by addition of CNF-g-PMMA.

Composite material immobilized silver nanoparticles (NPs) on the surface of cellulose nanofibers (CNF) was prepared using a high-pressure wet-type jet mill. A mixture both containing an aqueous silver nitrate solution and a CNF suspension was prepared as a raw starting material. The mixture was pulverized with the high-pressure wet-type jet mill at a pressure of 100 or 200 MPa. An X-ray diffraction pattern of the obtained sample revealed the presence of not only cellulose type I crystallites but also silver metal crystallites. According to observation by field-emission scanning electron microscopy, it was found that many silver NPs were immobilized on the surface of CNF. Note that almost all the silver NPs were well dispersed on the surface of CNF. It was cleared that the silver NPs had a spherical in shape with an average particle size of about 3 nm by the transmission electron microscope observation. The average size of the silver NPs slightly increased with the number of jet milling cycles, however, the change in the discharge pressure of the high-pressure wet-type jet mill did not affect the NPs size. The silver content in the composite materials increased with increasing both the number of jet milling cycles and the discharge pressure. The silver NPs were deposited by using the thermal energy released in the jet milling process, and their grain growth was then inhibited because the suspension was cooled immediately through the cooling tube. Therefore, it was assumed that silver NPs with a narrow size distribution could be immobilized on the surface of CNF.

A novel and ultrasensitive electrochemical immunosensor based on nanocellulose-Ti3C2Tx@ZrO2 nano framework for the detection of ovalbumin

Chiroptical properties of cellulose nanofibers (CNFs), especially optical chirality-inducing abilities, are crucial subjects to be explored for the development of CNF as a new class of optical materials. This study investigated experimentally the induced circular dichroism (CD) of the positively charged achiral dye molecules thioflavin T (ThT), toluidine blue O (TBO), and methylene blue (MB), adsorbed on 2,2,6,6-tetrametylpiperidine (TEMPO)-oxidized CNFs in aqueous suspensions. The achiral dyes exhibited CD spectra of the sigmoidal positive exciton-coupling shape, suggesting the effect of the right-handed helicity of the fiber. The observed CD intensities were proportional to the concentrations of the bound dye molecules. The TBO-CNF systems could be used for a reproducible titration method of the total amount of carboxylate ions on the surface of CNF, which gave a value of 2.0 ± 0.3 mmol/g. The Langmuir isotherm was applicable to the adsorption equilibrium between CNFs and the dye molecules, though a stacking effect was suggested in ThT systems, and a dimerization effect was found in MB systems. Furthermore, it was discovered that sweeping the dye-adsorbed 0.2% CNF suspension by a Cu wire in a 1 mm optical cell induced the positive and negative linear dichroism (LD) spectra of the dye molecules, depending on the vertical and horizontal sweeping directions, respectively. The hydrodynamic orientation of CNFs by the "wire-sweeping" was confirmed by the measurement of the linear birefringence (LB) of CNFs. A comparison between the angular dependences of the LD of the dye and the LB of the CNF in an identical sample suggested that the averaged angle between the electron transition moment of the adsorbed dye molecule and the long axis of the fiber was between 45° and 135°.

In this paper, a new method is introduced for producing multi-functional cellulose nanofibers in order to achieve the biodegradable materials for various applications with a minimal amount of potentially toxic materials. Cellulose nanofibers (CNFs) were fabricated by electrospinning cellulose acetate solution followed by deacetylation. The CNFs were then treated with silver nitrate, ammonia, and sodium hydroxide and subsequently with dopamine as reducing and adhesive agent. Ag ions on the CNF surface were photo-reduced to Ag nanoparticles (NPs) using UVA irradiation to produce a dense layer of silver nanoparticles on the nanofibers. This is based on the simultaneous formation of polydopamine and Ag NPs on CNFs. Overall, this is a fast, simple, and efficient procedure that takes place in a conventional method at ambient temperature. The crystalline structure of CNFs decorated with AgNPs was studied by X-ray diffraction. Field-emission scanning electron microscopy and energy-dispersive X-ray patterns showed uniform distribution of silver nanoparticles on the CNF surface. Incorporation of AgNPs on the CNF surface via dopamine improved the electrical conductivity and also the tensile strength of the nanomat. The CNFs decorated with AgNPs exhibited a low electrical resistivity around 35 KΩ/square and a tensile strength of 87% higher than untreated CNFs.

A variety of lignocellulosic raw materials have been previously reported for the production of cellulose and cellulose derivatives, but little research effort has been dedicated to producing cellulose from Hyparrhenia filipendula. In this study, cellulose nanofibers (CNFs) were extracted from Hyparrhenia filipendula waste straws via sulphuric acid hydrolysis. The straws were pretreated with a combination of physiochemical processes and hydrolyzed using sulphuric acid at three different concentrations (1 M, 3 M and 5.6 M) for 2 h at 80 °C. The properties of the CNFs was checked by Fourier Transform Infrared spectroscopy (FTIR) for surface chemistry, X-ray diffraction (XRD) for crystallinity, Scanning Electron microscopy and Transmission electron microscopy (TEM) for morphology. A high-performance liquid chromatograph (HPLC) was used to quantify the amount of biopolymers in the CNFs. The results show that CNFs, denoted as CNF 1, CNF 3, and CNF 5.6 for 1 M, 3 M, and 5.6 M sulphuric acid, respectively, were successfully extracted at the various concentrations of sulphuric acid. The cellulose content of CNF1, CNF3, and CNF5.6 determined by HPLC analysis were 85%, 77% and 78% respectively. Also, the hemicellulose content in CNF 1, CNF 3, and CNF 5.6 was 10%, 15%, and 12% respectively, showing a high carbohydrate content of the CNFs. The FTIR spectra confirm the absence of characteristic peaks for lignin in the CNFs. The XRD analysis reveals presence of characteristic cellulose Iβ peaks at 2θ of 18°, 26°, and 40° with the crystallinity of 78%, 74% and 73% for CNF1, CNF3 and CNF5.6, respectively. Moreover, SEM analysis shows the deposition of lignin polycondensate on the surface of CNF 1, CNF 3, and CNF 5.6 while the bleached sample has a smooth and glossy appearance. The TEM analysis shows long unbranched nano-sized fibers for CNF 1 and shorter fibrous network of fibers for CNF 3, and CNF 5.6. The average diameter of the fibers, measured with ImageJ software is 40 nm for CNF 1, 57 nm for CNF 3, and 92 nm for CNF 5.6. CNFs were successfully produced from Hyparrhenia filipendula and reported for the first time in open literature. In view of the structure and properties of the produced CNFs, they are a potential material for value-added applications such as polymer matrices, films, and membranes, thus enabling efficient utilization of agricultural waste.

A family of thermoresponsive poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) was synthesized via a novel silver-promoted decarboxylative polymerization approach. This method relies on the oxidative decarboxylation of carboxylic acid groups to initiate free radicals on the surface of CNFs. The polymerization reaction employs relatively mild reaction conditions and can be performed in a one-step, one-pot fashion. This rapid reaction forms a C─C bond between CNF and PNIPAM, along with the formation of free polymer in solution. The degree of functionalization (DF) and the amount of PNIPAM grafted can be controlled by the Ag concentration in the reaction. Similar to native bulk PNIPAM, PNIPAM-grafted CNFs (PNIPAM-g-CNFs) show remarkable thermoresponsive properties, albeit exhibiting a slight hysteresis between the heating and cooling stages. Grafting PNIPAM from CNFs changes its cloud point from about 32 to 36 °C, influenced by the hydrophilic nature of CNFs. Unlike physical blending, covalently tethering PNIPAM transforms the originally inert CNFs into thermosensitive biomaterials. The Ag concentration used does not significantly change the cloud point of PNIPAM-g-CNFs, while the cloud point slightly decreases with fiber concentration. Rheological studies demonstrated the sol-gel transition of PNIPAM-g-CNFs and revealed that the storage modulus (G') above cloud point increases with the amount of PNIPAM grafted. The novel chemistry developed paves the way for the polymerization of any vinyl monomer from the surface of CNFs and carbohydrates. This study validates a novel approach to graft PNIPAM from CNFs for the synthesis of new thermoresponsive and transparent hydrogels for a wide range of applications.

Today, enzymatic treatment is a progressive field in combating biofilm producing pathogens. In this regard, serratiopeptidase, a medicinally important metalloprotease, has been recently highlighted as an enzyme with proved anti-biofilm activity. In the present study, in order to increase the long-lasting effects of the enzyme, serratiopeptidase and the novel engineered forms with enhanced anti-biofilm activity were immobilized on the surface of cellulose nanofibers (CNFs) as a natural polymer with eminent properties. For this, recombinant serratiopeptidases including the native and previously designed enzymes were produced, purified and conjugated to the CNF by chemical and physical methods. Immobilization was confirmed using different scanning and microscopic methods. The enzyme activity was assessed using casein hydrolysis test. Enzyme release analysis was performed using dialysis tube method. Anti-biofilm activity of free and immobilized enzymes has been examined on Staphylococcus aureus and Pseudomonas aeruginosa strains. Finally, cytotoxicity of enzyme-conjugated CNFs was performed by MTT assay. The casein hydrolysis results confirmed fixation of all recombinant enzymes on CNFs by chemical method; however, inadequate fixation of these enzymes was found using cold atmospheric plasma (CAP). The AFM, FTIR, and SEM analysis confirmed appropriate conjugation of enzymes on the surface of CNFs. Immobilization of enzymes on CNFs improved the anti-biofilm activity of serratiopeptidase enzymes. Interestingly, the novel engineered serratiopeptidase (T344 [8-339ss]) exhibited the highest anti-biofilm activity in both conjugated and non-conjugated forms. In conclusion, incorporation of serratiopeptidases into CNFs improves their anti-biofilm activities without baring any cytotoxicity. KEY POINTS: • Enzymes were successfully immobilized on cellulose nanofibers using chemical method. • Immobilization of enzymes on CNFs improved their anti-biofilm activity. • T344 [8-339ss] exhibited the highest anti-biofilm activity in both conjugated and non-conjugated forms.

Suppressed photocatalytic activity of ZnO based Core@Shell and RCore@Shell nanostructure incorporated in the cellulose nanofiber

Study on cellulose nanofibers (CNF) distribution behaviors and their roles in improving paper property

The aim of this study was to synthesize hydrophobic cellulose nanofibers (CNFs) using different chemical treatments including polymer and molecular grafting. For polymer grafting, immobilizing poly (butyl acrylate) (PBA) and poly (methyl methacrylate) (PMMA) on CNFs were implemented by the free radical method. Also, acetyl groups were introduced directly onto the CNFs surface by acetic anhydride for molecular grafting. The gravimetric and X-ray photoelectron spectroscopy analysis showed the high grafting density of PMMA on the surface of CNFs. AFM results revealed that molecular grafting created non-uniformity on the CNFs surface, as compared to polymer brushes. In addition, thermodynamic work of adhesion and work of cohesion for the modified CNFs were reduced in water and diiodomethane solvents. Dispersion factor was studied to indicate the dispersibility of CNFs in polar and non-polar media. Dispersion energy was reduced after modification as a result of decreasing interfacial tension and the dispersibility of modified CNFs was improved in diiodomethane.

Materials for wearable devices, tissue engineering and bio-sensing applications require both antibacterial activity to prevent bacterial infection and biofilm formation, and electrical conductivity to electric signals inside and outside of the human body. Recently, cellulose nanofibers have been utilized for various applications but cellulose itself has neither antibacterial activity nor conductivity. Here, an antibacterial and electrically conductive composite was formed by generating catechol mediated silver nanoparticles (AgNPs) on the surface of cellulose nanofibers. The chemically immobilized catechol moiety on the nanofibrous cellulose network reduced Ag+ to form AgNPs on the cellulose nanofiber. The AgNPs cellulose composite showed excellent antibacterial efficacy against both Gram-positive and Gram-negative bacteria. In addition, the catechol conjugation and the addition of AgNP induced anisotropic self-alignment of the cellulose nanofibers which enhances electrical and mechanical properties of the composite. Therefore, the composite containing AgNPs and anisotropic aligned the cellulose nanofiber may be useful for biomedical applications.

Green chemistry approaches for extraction of cellulose nanofibers (CNFs): A comparison of mineral and organic acids

This study introduces the development of a novel bio-nano composite via the dispersion of cellulose nanofibers (CNF) in epoxy. The surface of cellulose nanofibers was functionalized using a two-step chemical treatment to enhance dispersion. The interfacial characteristics of CNF were improved using alcohol/acetone treatments. The modified CNF (M-CNF) demonstrated enhanced compatibility and improved dispersion in the epoxy matrix as evidenced by scanning electron microscopy. Based on the analysis of X-ray diffraction patterns, M-CNF did not disturb the crystalline phases at the interface. The results of mechanical testing showed that M-CNF worked as a reinforcing agent in the bio-nano composite. The flexural modulus increased from 1.4 to 3.7 GPa when M-CNF was introduced. A similar trend was observed for tensile strength and impact resistance. The optimum performance characteristics were observed at M-CNF of 0.6%. At higher dosages, some agglomeration was observed, which weakened the interfacial properties. This study promotes sustainability and resource conservation while offering CNF as a sustainable reinforcing agent to develop bio-nano composites.

Bio-inspired cellulose nanofiber-reinforced soy protein resin adhesives with dopamine-induced codeposition of “water-resistant” interphases